User:Serendipodous/indigo/page 13

Betelgeuse

15 km/sec. 1 km/sec is Mach 3. If earth span that fast, a day would last 45 minutes. For Betelgeuse, a full rotation takes eight years. (8.189)

Many fluctuations of Betelgeuse recur over eight year cycles, suggesting they are tied to rotation.

Did Betelgeuse swallow a star?

Dipped in brightness by a full visual magnitude

studied over 100 days, five years, 425 days

unprecedented dimming in the time of detailed study (40 years)

Sheer statiscial probability suggests that Betelgeuse is not likely to go supernova for a hundred thousand years

No one has ever actually seen a star, let alone a naked eye star, explode.

Dimming mionths before an explosion?

Not a symmetrical star

has ejected shells of gas to the distance of neptune

blocked by dust? titanium oxide suggests the star has cooled 100 degrees, and has gotten bigger

The stars rotation rade should slow as it expands

First it would become brighter than Venus, then -10, close to the full moon, cast shadows, even read by it.

1836: John Herschel noted Betelgeuse's variability while at the cape of good hope, (2nd brightest to brightest over 4 months) then forgot and rediscovered it four years later

Sima Qian: historical record, 1st century BC: White like Sirius, red like Antares, yellow like Betelgeuse, and blue like Bellatrix"

Ptolemy described Sirius as red

The largest angular diameter of any star other than the sun

an ideal case study of the advanced stages of stellar evolution

In 1995, the Hubble Space Telescope UV, the first conventional-telescope image of the disk of another star.

Because ultraviolet light is absorbed by the Earth's atmosphere, observations at these wavelengths are best performed by space telescopes.

Like earlier pictures, this image contained a bright patch indicating a region in the southwestern quadrant 2000 K hotter than the stellar surface.

Subsequent ultraviolet spectra taken with the Goddard High Resolution Spectrograph suggested that the hot spot was one of Betelgeuse's poles of rotation. This would give the rotational axis an inclination of about 20° to the direction of Earth, and a position angle from celestial North of about 55°.

Both the light curve and the imagery indicate the appearance of intermittent bright spots associated with irregular variability in the star’s luminosity and temperature.

The chromosphere has exhibited a periodic (∼420 day) modulation in the optical and UV flux most likely associated with photospheric pulsations that later became substantially weaker, and disappeared

A shell of circumstellar material has also been detected around this star

The first parallax distance measurements reported by Hipparcos (∼131 pc) and Tycho (∼54 pc) disagreed by more than a factor of two (ESA 1997).

This was well outside the range of quoted errors. However, the more recent VLA-Hipparcos distance to Betelgeuse of ∼ 197±45 pc has been derived from multi-wavelength observations.

This results in extended atmospheres and large convective motion which produces asymmetry along with variability in the surface temperature and luminosity.

In addition to the random variability in surface luminosity and temperature and intermittent periodic variability, the diameter of this star seems to change with time

It is now recognized that there are multiple bows shocks indicating that the mass loss from this star is episodic rather than continuous.

Betelgeuse is irregularly shaped, bumps

These bumps are convection cells that, unlike the sun, travel almost to the core. Low gravity and high speed (30 km/sec) push them above the surface

cloud of gas and dust 3 light yeras wide

RSGs are magnifying glasses, revealing faults in previous calculations

A red supergiant must have a mass of 8 Earth masses

1-10 millin years on main sequence

CNO cycle main sequence

1=100 thousand years transform into RSGs

temp <~4500 k and lum 10000 times that of the sun

core helium fusion or carbon fusion and an extended fully convected envelope

100-1000 solar radii

move back along the hr diagram to yellow supergiants or wolf-reyet stars (mass loss stripping away outer layers?)

produce massive amounts of dust

complex cirxcumstellar environment

Type II-P supernovae

Stars beyond a certain mass limit (50-60 solar masses) will not become red supergiants

few 25-40 sol mass RSGs observed

Betelgeuse radius averages point to 862 and 890 Rsun

more than half the mass loss of a massive star occurs after it leaves the main sequence

instability strip; stars begin to lose grip on their outer layers, they begin to flutter, and fall back, burst up, fall back

radiation heats dust in outer layers until it blows its top.

disentangling the sources of variability is daunting, at times impossible

dust can obscure the surface

Potter

• Artemus Olgletree
• Vesto Melvin Slipher
• Hannalore Gerling-Dunsmore

“First in, last out”

However, that solution would be hard to accept, as it predicts a future for our own civilization that is even worse than extinction.

Most likely, they simply won’t notice, the same way a construction crew demolishes an anthill to build real estate because they lack incentive to protect it. And even if the individuals themselves try their best to be cautious, their von Neumann probes probably don’t.

This problem is similar to the infamous “Tragedy of the commons”. The incentive to grab all available resources is strong, and it only takes one bad actor to ruin the equilibrium, with no possibility to prevent them from appearing at interstellar scale.

The only explanation is the invocation of the anthropic principle. We are the first to arrive at the stage. And, most likely, will be the last to leave.

But I certainly hope I am wrong. The only way to find out is to continue exploring the Universe and searching for alien life.

Sagan and Newman

Tipler estimates that, assuming a speed of 3 light years every 10 thousand years, von Neumann probes could replicate at a speed of once every 10,000 years. Assuming that each probe weight a million kg, they could convert the entire galaxy into themselves within 1.5 million years.

Stephen J Gould: "I must confess taht I simply don't know how to react to such arguments. I have enough trouble predicting the plans and reactions of people closest to me. I am usually baffled by the thoughts and accomplishments of people in different cultures. I'll be damned if I can say with certainty what some extraterrestrial form of intelligence might do.

stephen webb argues that no society would want to develop berserkers. But a fault in the code could result in their creation via von neumann probe

Inocculation? Why are we here?

Sagan: if von neumann probes can be controlled, they may have bypassed our system deliberately

If they cannot be controlled, then they would have anhillated our entire universe by now.

It would be prudent for any civilization not to develop von neumann probes in the fisrt place, and to combat any that it observed

no host specificity. von neumann probes can convert any system into more of themselves.

Brin, the great silence

"the effect of deadly probes on L is profound, and I love lucy is well past tau ceti by now"

the idea that deadly probes have anhillated all intelligence answers the arguments against the Fermi paradox

Polynesia; more sanguinary than sanguine

without ftl the polystellans would face intense internal competition for asteroid resources and solar power.

spacebourne could attack the planet-bound, free from gravity wells

selfish empires are likely to expand more quickly than conscientious ones

deadly probes, ecological holocaust- consistent with observation and with non-exclusivity. Exclusivity= "why would everyone do it")

diversity should prevail unless there exists a mechanism to enforce conformity

life appears quickly in the fossil record; the process of abiogensis may not have been random

Miller and Urey contended that poly alpha amino acids would be present in any alien life, and that it would likely share 75 percent of its basic chemical structure with Earth

Intelligence is common (primates, cetaceans)

Crises of survival are hard to generalise beyond Earth

chance of reaching technology: all it takes is 1 in a thousand; it will be the exceptions that make the rules

Even the slowest predictions could be smeared out by the rotation of the galaxy, reducing colonisation time by a factor of four.

Given our movement through the galaxy, any edict would have to be galaxy wide

Issues such as resource exhaustion and transcendence fall foul of non exclusivity

Connected to berserker

Grey 2016

https://blogs.scientificamerican.com/guest-blog/the-fermi-paradox-is-not-fermi-s-and-it-is-not-a-paradox/

Fermi was considering the feasibility of interstellar travel, not the existence of ETI. Hart proposed the non-existence of ETI

Berserker

carmpan telepathic peaceful (20th century radio contact)

Berserkers stramble minds

Berserkers are random (tied to radioactive decay?) to ensure they are unpredictable

Turchlin

The possibility that ETI may not exist suggests the great filter is ahead of us, which means a global catastrophic event is inevitable (CGR are merely probable?)

At near ligfht speed a von neumann wave would leave little time for defence, and may destroy us instantly

It's highly likely that if any nearby EITs wished us harm, they would have done it by now

a kiloton impactor aty 99% c would have an impact force of 130 gigatons, massive enough to split atoms and create radioactive particles that would blanket the earth like a coblat bomb

Given that basic lifesigns have been present on Earth for billions of years, it would appear such signs are not enough to trigger such an attack

Presumably berserkers are waiting for some unspecified technological threshold, or we wouldn't be here.

teh biggest risk in the non-existence of ETI, since that would lead to a high probablilty for our own extinction

Sanberg and Armstrong

1. Cause the great silence 2. Be compatible with our existence 3. Be silent enough not to be visible 4. Be unstoppable by any civilization (immunisation proposed by sagan)

Either one overriding species keeps a lid on everyone else

or multiple species exist in a state of stalemate

Earth is in a very "normal" position in the galaxy- not a halo star or a newborn

1 rules out the possibility of not perfect probes missing us

Tipler

Avoiding a rogue Neumann probe:

The program can be so integrated that it fails safe, ceasing to work if the control mechanism fails

The sapient species could travel with the probes, keeping them under control

Third, they may just leave them be. As sentient beings evolve, racism and interpersonal violence declines.

Even if the probes decided to declare war on organic life, they would still simply replace one intelligence with another, and likely launch their own von neumann probes

Hygeia

"Thanks to the unique capability of the SPHERE instrument on the VLT, which is one of the most powerful imaging systems in the world, we could resolve Hygiea's shape, which turns out to be nearly spherical," says lead researcher Pierre Vernazza from the Laboratoire d'Astrophysique de Marseille in France. "Thanks to these images, Hygiea may be reclassified as a dwarf planet, so far the smallest in the Solar System." The team also used the SPHERE observations to constrain Hygiea's size, putting its diameter at just over 430 km. Pluto, the most famous of dwarf planets, has a diameter close to 2400 km, while Ceres is close to 950 km in size. urprisingly, the observations also revealed that Hygiea lacks the very large impact crater that scientists expected to see on its surface, the team report in the study published today in Nature Astronomy. Hygiea is the main member of one of the largest asteroid families, with close to 7000 members that all originated from the same parent body. Astronomers expected the event that led to the formation of this numerous family to have left a large, deep mark on Hygiea. The team decided to investigate further. Using numerical simulations, they deduced that Hygiea's spherical shape and large family of asteroids are likely the result of a major head-on collision with a large projectile of diameter between 75 and 150 km. Their simulations show this violent impact, thought to have occurred about 2 billion years ago, completely shattered the parent body. Once the left-over pieces reassembled, they gave Hygiea its round shape and thousands of companion asteroids. "Such a collision between two large bodies in the asteroid belt is unique in the last 3-4 billion years," says Pavel Ševeček, a Ph.D. student at the Astronomical Institute of Charles University who also participated in the study.

discs

December

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) found a young star surrounded by an astonishing mass of gas. The star, called 49 Ceti, is 40 million years old and conventional theories of planet formation predict that the gas should have disappeared by that age. The enigmatically large amount of gas requests a reconsideration of our current understanding of planet formation. Thanks to ALMA's high resolution, the team revealed the spatial distribution of carbon atoms in a debris disk for the first time. Carbon atoms are more widely distributed than carbon monoxide, the second most abundant molecules around young stars, hydrogen molecules being the most abundant. The amount of carbon atoms is so large that the team even detected faint radio waves from a rarer form of carbon, 13C. This is the first detection of the 13C emission at 492 GHz in any astronomical object, which is usually hidden behind the emission of normal 12C. What is the origin of the gas? Researchers have suggested two possibilities. One is that it is remnant gas that survived the dissipation process in the final phase of planet formation. The amount of gas around 49 Ceti is, however, comparable to those around much younger stars in the active planet formation phase. There are no theoretical models to explain how so much gas could have persisted for so long. The other possibility is that the gas was released by the collisions of small bodies like comets. But the number of collisions needed to explain the large amount of gas around 49 Ceti is too large to be accommodated in current theories. The present ALMA results prompt a reconsideration of the planet formation models.

September

It is surrounded by a disc of dust and gas—a so-called protoplanetary disc. It is within these discs that young planets are born. Using a radio telescope in the Atacama Desert in Chile, researchers were able to detect an extremely faint signal showing the existence of a rare form of carbon monoxide—known as an isotopologue (13C17O). The detection has allowed an international collaboration of scientists, led by the University of Leeds, to measure the mass of the gas in the disc more accurately than ever before. The results show that disc is much heavier—or more 'massive' - than previously thought.

The research team were the first to discover a new planet inside a protoplanetary disc. Using the same methods, the scientists have now discovered a new planet in the middle of a gap inside the surrounding disc. Lead study author Dr. Christophe Pinte, an ARC Future Fellow at the Monash School of Physics and Astronomy.

To test their theory, the researchers looked at three protoplanetary disks from the Disk Substructures at High Angular Resolution Project (DSHARP), a survey conducted by a large consortium of astronomers. DSHARP focuses on images of 20 nearby, bright and large protoplanetary disks taken by the Atacama Large Millimeter/submillimeter Array telescope in Chile. "We were looking for disks in which it was pretty clear a planet was there," Rice said. "If a disk has clear gaps in it, like several of the DSHARP disks do, it's possible to extrapolate what type of planet would be there. Then, we can simulate the systems to see how much material should be ejected over time." "This idea nicely explains the high density of these objects drifting in interstellar space, and it shows that we should be finding up to hundreds of these objects with upcoming surveys coming online next year," Laughlin said.

A second planet has been discovered circling Beta Pictoris, a fledgling star in our own galaxy offering astronomers a rare glimpse of a planetary system in the making, according to a study published Monday. "We talking about a giant planet about 3,000 times more massive than Earth, situated 2.7 times further from its star than the Earth is from the Sun," said Anne-Marie Lagrange, an astronomer at France's National Centre for Scientific Research and lead author of a study in Nature Astronomy. The new planet, β Pictoris c, completes its orbit roughly every 1,200 days. Like its big sister β Pictoris b, discovered by Lagrange and her team in 2009, it is a gassy giant. Visible with the naked eye, Beta Pictoris—with a mass nearly twice that of the Sun—is a newborn by comparison: only 23 million years old.

May

Just about a year after the launch of the NASA mission TESS, the first three comets orbiting the nearby star Beta Pictoris outside our solar system were discovered with data from the space telescope.

Sun

March

A combination of favourable conditions and an element of luck enabled the team to determine the strength of the flare's magnetic field with unprecedented accuracy. This is the first time we have been able to measure accurately the magnetic field of the coronal loops, the building blocks of the sun's magnetic corona, which such a level of accuracy." we have very few measurements of its strength and spatial characteristics.

June

A group of researchers has identified and characterized for the first time in a complete way a powerful eruption in the atmosphere of the active star HR 9024, marked by an intense flash of X-rays followed by the emission of a giant bubble of plasma, ie hot gas containing charged particles. This is the first time a coronal mass ejection, or CME, has been seen in a star other than our Sun. The corona is the outer atmosphere of a star.

New research in AGU's journal Space Weather indicates storms like the Carrington Event are not as rare as scientists thought and could happen every few decades, seriously damaging modern communication and navigation systems around the globe. "The Carrington Event was considered to be the worst-case scenario for space weather events against the modern civilization… but if it comes several times a century, we have to reconsider how to prepare against and mitigate that kind of space weather hazard," The researchers collected observations of the storm's auroras from the Russian Central Observatory, Japanese diaries, and newspapers from Portugal, Spain, Australia, New Zealand, Mexico and Brazil. They then compared these observations to previous reports of the storm from the Western Hemisphere, like ship logs, contemporary scientific journals, and more newspapers. After reconstructing the storms around the Carrington Event, the researchers compared the solar storm to other storms in 1872, 1909, 1921, and 1989 and found two of them—those in 1872 and 1921—were comparable to this event. The 1989 event caused a serious blackout throughout all of Quebec, Canada. This means events like the Carrington may not be as legendary and elusive as once thought, and scientists need to consider the hazards of such events more seriously than before, according to Hayakawa.

Eccentricites

October

Surprisingly, the planets with the highest masses tend to be those with the highest eccentricities, even though the inertia of a larger mass should make it harder to budge from its initial orbit. This counter-intuitive observation prompted astronomers at UC Santa Cruz to explore the evolution of planetary systems using computer simulations. Their results, reported in a paper published in Astrophysical Journal Letters, suggest a crucial role for a giant-impacts phase in the evolution of high-mass planetary systems, leading to collisional growth of multiple giant planets with close-in orbits. "A giant planet is not as easily scattered into an eccentric orbit as a smaller planet, but if there are multiple giant planets close to the host star, their gravitational interactions are more likely scatter them into eccentric orbits," explained first author Renata Frelikh, a graduate student in astronomy and astrophysics at UC Santa Cruz.

August

HR 5183b "This planet is unlike the planets in our solar system, but more than that, it is unlike any other exoplanets we have discovered so far," says Sarah Blunt, a Caltech graduate student and first author on the new study publishing in The Astronomical Journal. "Other planets detected far away from their stars tend to have very low eccentricities, meaning that their orbits are more circular. The fact that this planet has such a high eccentricity speaks to some difference in the way that it either formed or evolved relative to the other planets." The astronomers have been watching the planet's star, called HR 5183, since the 1990s, but do not have data corresponding to one full orbit of the planet, called HR 5183 b, because it circles its star roughly every 45 to 100 years. The team instead found the planet because of its strange orbit. "This newfound planet basically would have come in like a wrecking ball," says Howard, "knocking anything in its way out of the system.

Having determined the physical properties of both stars, such as their mass, size and age, through asteroseismology, the authors then focused their attention on the evolutionary state of HD 203949. Their aim was to understand how its planet could have avoided engulfment, since the envelope of the star would have expanded well beyond the current planetary orbit during the red-giant phase of evolution. Co-author Vardan Adibekyan (IA & Universidade do Porto) says, "This study is a perfect demonstration of how stellar and exoplanetary astrophysics are linked together. Stellar analysis seems to suggest that the star is too evolved to still host a planet at such a short orbital distance, while from the exoplanet analysis, we know that the planet is there." By performing extensive numerical simulations, the team thinks that star-planet tides might have brought the planet inward from its original, wider orbit, placing it where we see it today. Adibekyan says, "The solution to this scientific dilemma is hidden in the simple fact that stars and their planets not only form, but also evolve together. In this particular case, the planet managed to avoid engulfment."

July

Sometimes, planets pass too close to each other and knock one another off course. This can result in a planet with an elliptical or "eccentric" orbit. Conventional wisdom says that a giant planet in eccentric orbit is like a wrecking ball for its planetary neighbors, making them unstable, upsetting weather systems, and reducing or eliminating the likelihood of life existing on them. Questioning this assumption, Kane and Caltech astronomer Sarah Blunt tested the stability of an Earth-like planet in the HR 5183 solar system. Their modeling work is documented in a paper newly published in the Astronomical Journal. Kane and Blunt calculated the giant planet's gravitational pull on an Earth analog as they both orbited their star. "In these simulations, the giant planet often had a catastrophic effect on the Earth twin, in many cases throwing it out of the solar system entirely," Kane said. "But in certain parts of the planetary system, the gravitational effect of the giant planet is remarkably small enough to allow the Earth-like planet to remain in a stable orbit." The team found that the smaller, terrestrial planet has the best chance of remaining stable within an area of the solar system called the habitable zone—which is the territory around a star that is warm enough to allow for liquid-water oceans on a planet.

White dwarfs

December

Researchers using ESO's Very Large Telescope have, for the first time, found evidence of a giant planet associated with a white dwarf star. The planet orbits the hot white dwarf, the remnant of a Sun-like star, at close range, causing its atmosphere to be stripped away and form a disc of gas around the star. This unique system hints at what our own Solar System might look like in the distant future. he white dwarf is small and, at a blistering 28 000 degrees Celsius (five times the Sun's temperature), extremely hot. By contrast, the planet is icy and large—at least twice as large as the star. Since it orbits the hot white dwarf at close range, making its way around it in just 10 days, the high-energy photons from the star are gradually blowing away the planet's atmosphere. Most of the gas escapes, but some is pulled into a disc swirling into the star at a rate of 3000 tonnes per second. It is this disc that makes the otherwise hidden Neptune-like planet visible.

October

The scientists, led by Alexandra Doyle, a UCLA graduate student of geochemistry and astrochemistry, developed a new method to analyze in detail the geochemistry of planets outside of our solar system. Doyle did so by analyzing the elements in rocks from asteroids or rocky planet fragments that orbited six white dwarf stars. "We're studying geochemistry in rocks from other stars, which is almost unheard of," Young said. "By observing these white dwarfs and the elements present in their atmosphere, we are observing the elements that are in the body that orbited the white dwarf," Doyle said. The white dwarf's large gravitational pull shreds the asteroid or planet fragment that is orbiting it, and the material falls onto the white dwarf, she said. "Observing a white dwarf is like doing an autopsy on the contents of what it has gobbled in its solar system."

May

University of Warwick. High viscosity exo-Earths are easily swallowed only if they reside at distances within twice the separation between the centre of the white dwarf and its destruction radius. These planets would be composed entirely of a dense core of heavier elements, with a similar composition to the 'heavy metal' planet discovered by another team of University of Warwick astronomers recently. That planet has avoided engulfment because it is as small as an asteroid.

Exoplanets

December

A surprising analysis of the composition of gas giant exoplanets and their host stars shows that there isn't a strong correlation between their compositions when it comes to elements heavier than hydrogen and helium, according to new work led by Carnegie's Johanna Teske and published in the Astronomical Journal. This finding has important implications for our understanding of the planetary formation process. One clue may come from the authors' combined results bundling the heavy elements into groupings that reflect their characteristics. The authors saw a tentative correlation between a planet's heavy elements and its host star's relative abundance of carbon and oxygen, which are called volatile elements, versus the rest of the elements included in this study, which fall into the group called refractory elements. These terms refer to the elements' low boiling points—volatility—or their high melting points—in the case of the refractory elements. Volatile elements may represent an ice-rich planetary composition, whereas refractory elements may indicate a rocky composition.

The team studied stars known as DMPP-1, DMPP-2 and DMPP-3. The planets discovered, DMPP-1b, DMPP-1c, DMPP-1d, DMPP-1e, DMPP-2b and DMPP-3Ab, are very close to the stars and are heated to temperatures of 1100 degrees C–1800 degrees C. At these temperatures, the atmosphere and even the rocky surface of the planet can be lost, and some of this material disperses to form a thin shroud of gas. This shroud filters the light from the star, producing clues that allowed the team to pick out the tiny fraction of stars with these unusual, very hot planets. With further study, the chemical composition of the shroud can be measured, revealing the type of rock on the surface of the hot planet.

"Super-Puffs" may sound like a new breakfast cereal. But it's actually the nickname for a unique and rare class of young exoplanets that have the density of cotton candy. Nothing like them exists in our solar system. New data from NASA's Hubble Space Telescope have provided the first clues to the chemistry of two of these super-puffy planets, which are located in the Kepler 51 system. This exoplanet system, which actually boasts three super-puffs orbiting a young Sun-like star, was discovered by NASA's Kepler space telescope in 2012. However, it wasn't until 2014 when the low densities of these planets were determined, to the surprise of many. The recent Hubble observations allowed a team of astronomers to refine the mass and size estimates for these worlds—independently confirming their "puffy" nature. Though no more than several times the mass of Earth, their hydrogen/helium atmospheres are so bloated they are nearly the size of Jupiter. In other words, these planets might look as big and bulky as Jupiter, but are roughly a hundred times lighter in terms of mass. How and why their atmospheres balloon outwards remains unknown, but this feature makes super-puffs prime targets for atmospheric investigation. Using Hubble, the team went looking for evidence of components, notably water, in the atmospheres of the planets, called Kepler-51 b and 51 d. Hubble observed the planets when they passed in front of their star, aiming to observe the infrared color of their sunsets. Astronomers deduced the amount of light absorbed by the atmosphere in infrared light. This type of observation allows scientists to look for the telltale signs of the planets' chemical constituents, such as water. To the amazement of the Hubble team, they found the spectra of both planets not to have any telltale chemical signatures. They attribute this result to clouds of particles high in their atmospheres. "This was completely unexpected," said Jessica Libby-Roberts of the University of Colorado, Boulder, "we had planned on observing large water absorption features, but they just weren't there. We were clouded out!" However, unlike Earth's water-clouds, the clouds on these planets may be composed of salt crystals or photochemical hazes, like those found on Saturn's largest moon, Titan

August

The planet in question, LHS 3844b, was discovered in 2018 by NASA's Transiting Exoplanet Survey Satellite, TESS, and was measured to be about 1.3 times larger than Earth. The planet zips around its star in just 11 hours, making it one of the fastest orbiting exoplanets known. The star itself is a small, cool M-dwarf that resides just 49 light-years from Earth. In a paper published today in Nature, the team reports that LHS 3844b likely has neither a thick, Venus-like atmosphere nor a thin, Earth-like atmosphere. Instead, the planet is probably more similar to Mercury—a blistering, bare rock. If an atmosphere ever existed, the researchers say the star's radiation likely blasted it away early in the planet's formation.

To overcome that hurdle, the researchers designed a new method to infer the occurrence rate of planets across a wide range of sizes and orbital distances. The new model simulates 'universes' of stars and planets and then 'observes' these simulated universes to determine how many of the planets would have been discovered by Kepler in each `universe.' "We used the final catalog of planets identified by Kepler and improved star properties from the European Space Agency's Gaia spacecraft to build our simulations," said Danley Hsu, a graduate student at Penn State and the first author of the paper. "By comparing the results to the planets cataloged by Kepler, we characterized the rate of planets per star and how that depends on planet size and orbital distance. Our novel approach allowed the team to account for several effects that have not been included in previous studies." Based on their simulations, the researchers estimate that planets very close to Earth in size, from three-quarters to one-and-a-half times the size of earth, with orbital periods ranging from 237 to 500 days, occur around approximately one in four stars. Importantly, their model quantifies the uncertainty in that estimate. They recommend that future planet-finding missions plan for a true rate that ranges from as low about one planet for every 33 stars to as high as nearly one planet for every two stars.

Normally, hot Jupiter planets are still cool enough inside to condense heavier elements such as magnesium and iron into clouds that remain in the planet's atmosphere. But that's not the case with WASP-121b, which is orbiting so close to its host star that the planet's upper atmosphere reaches a blazing 4,600 degrees Fahrenheit. The planet is so close, in fact, that it is being ripped apart by the star's gravity, giving the planet an oblique football shape. The WASP-121 star system resides about 900 light-years from Earth. "Heavy metals have been seen in other hot Jupiters before, but only in the lower atmosphere," explained lead researcher David Sing of Johns Hopkins University. "With WASP-121b, we see magnesium and iron gas so far away from the planet that they're not gravitationally bound. The heavy metals are escaping partly because the planet is so big and puffy that its gravity is relatively weak. This is a planet being actively stripped of its atmosphere."

The blistering planet GJ 357 b, picked out by NASA's Transiting Exoplanet Survey Satellite, lies about 31 light-years away in the constellation Hydra. It's only 22% larger than Earth and circles its star every 3.9 days—tracing an orbit that's 11 times closer to its star than Mercury's is to our sun. This means that even though its M-dwarf star is roughly 40% cooler than our sun, the planet is in all likelihood searingly hot—probably 490 degrees Fahrenheit or so—even without the insulating effects of an atmosphere. Astronomers used information from the ground-based telescopes to confirm GJ 357 b's existence. In the process, they noticed clues that an additional pair of planets was also circling the same star. GJ 357 c weighs in at about 3.4 times Earth's mass, if not more, and orbits the star every 9.1 days at a distance more than double that of GJ 357 b. This proximity keeps the temperature at around 260 degrees Fahrenheit—not quite as singed as planet b, but still pretty toasty. It's the third planet, GJ 357 d, that actually holds some potential as a habitable world. It weighs at least 6.1 Earth masses and circles the star at a much greater distance, completing an orbit in 55.7 days. Even though this is just one-fifth the distance of the Earth to our sun, GJ 357 d's dim star leaves the surface very cold. Without an atmosphere, the thermometer at the surface would hover around 64 degrees Fahrenheit below zero—meaning no liquid water on the surface. However, if GJ 357 d does turn out to have an atmosphere, this could be a game changer, according to a report that will be published in the journal Astronomy & Astrophysics. A dense atmosphere with the right composition could trap some warmth and allow water to remain liquid on the planet's surface. That's similar to what scientists think happened on Mars, which today is frigid and dry but may once have had a thick atmosphere that allowed liquid water to leave marks all over its ruddy face.

June

The combination of observations made with the CARMENES spectrograph on the 3.5m telescope at Calar Alto Observatory (Almería), and the HARPS-N spectrograph on the National Galileo Telescope (TNG) at the Roque de los Muchachos Observatory (Garafía, La Palma) has enabled a team from the Instituto de Astrofísica de Canarias (IAC) to reveal new details about this extrasolar planet, which has a surface temperature of around 2000 K. MASCARA-2B/KELT-20b is an ultra hot Jupiter. It belongs to a new group of exoplanets, the hottest known until now, which can reach temperatures at the surface of over 2,000 K. hydrogen beta, singly ionized iron and magnesium with data from HARPS-N, while the presence of ionized calcium was detected only by using CARMENES. Neutral sodium and hydrogen alpha are detected with both instruments."

An international team led by the University of Göttingen (Germany) with participation by researchers from the Instituto de Astrofísica de Canarias (IAC) have discovered, using the CARMENES high-resolution spectrograph at the Calar Alto Observatory (Almería) two new planets like the Earth around one of the closest stars within our galactic neighbourhood. The Teegarden star is only 12.5 light years away. It is a red dwarf in the direction of the constellation of Aries. Its surface temperature is 2,700 degrees C, and its mass is only one-tenth that of the sun. Even though it is so near, its faintness impeded its discovery until 2003. "We have been observing this star for three years to look for periodic variations in its velocity, explains Mathias Zechmeister, a researcher at the University of Göttingen, the first author of the paper. The observations showed that two planets are orbiting it, both of them similar to the planets in the inner part of the Solar System. They are just a little bigger than the Earth and are situated in the "inhabitable zone" where water can exist as a liquid. "It is possible that the two planets are part of a larger system," says Stefan Dreizler, another University of Göttingen researcher and a co-author of the paper. Photometric campaigns on this star have been carried out with instruments such as Muscat2 on the Carlos Sánchez Telescope at the Teide Observatory (Tenerife), and with the network of telescopes of the Las Cumbres Observatory, among others. These studies demonstrate that the signals of the two planets cannot be due to the activity of the star, even though we could not detect the transits of the two new planets," says Victor Sánchez Béjar, an IAC researcher and another author of the article which is being published in the journal Astronomy and Astrophysics. For the transit method to be viable, the planets must pass across the face of the stellar disc and block some of the light from the star during a short time, which means that it must lie on a line joining the sun and the Earth. This lucky alignment occurs for only a small fraction of planetary systems. The type of star to which the Teegarden star belongs consists of the smallest for which researchers can measure the masses of their planets with current technology.

The Kepler-9 system, for example, appears to have two planets with densities respectively of 0.42 and 0.31 grams per cubic centimeter (Saturn is 0.69 grams per cubic centimeter.) The striking results cast some doubt on one or more parts of the transit timing variation methodology and created a long-standing concern. CfA astronomers David Charbonneau, David Latham, Mercedes Lopez-Morales, and David Phillips, and their colleagues tested the reliability of the method by measuring the densities of the Kepler-9 planets using the radial velocity method, its two Saturn-like planets being among a small group of exoplanets whose masses can be measured (if just barely) with either technique. They used the HARPS-N spectrometer on the Telescopio Nazionale Galileo in La Palma in sixteen observing epochs; HARPS-N can typically measure velocity variations with an error as tiny as about twenty miles an hour. Their results confirm the very low densities obtained by the transit-timing method, and verify the power of the transit-variation method.

May

Three similar exocomet systems have recently been found around three other stars during data analysis by NASA's Kepler mission. The researchers suggest that exocomets are more likely to be found around young stars. "The space telescope Kepler concentrated on older stars similar to the Sun in a relatively small area in the sky. TESS, on the other hand, observes stars all over the sky, including young stars.

KELT-9 b is the hottest exoplanet known to date. In the summer of 2018, a joint team of astronomers from the universities of Bern and Geneva found signatures of gaseous iron and titanium in its atmosphere. Now these researchers have also been able to detect traces of vaporized sodium, magnesium, chromium, and the rare-Earth metals scandium and yttrium. April

"It took 20 years and many more observers," says Emily Rickman, first author of the study and a researcher in the Astronomy Department of the UNIGE Faculty of Science. meter per second spectrograph. Five new planets have been discovered, and the orbits of four others have been precisely defined. All these planets have periods of revolution between 15.6 and 40.4 years, with masses ranging approximately from 3 to 27 times that of Jupiter. This study contributes to increasing the list of 26 planets with a rotation period greater than 15 years, "but above all, it provides us with new targets for direct imaging," concludes the Geneva researcher.

Fabio Del Sordo with the University of Crete and Mario Damasso with the Observatory of Turin. The pair went on to suggest that if their findings pan out, they believe the exoplanet would have a mass approximately six times that of Earth, putting it in the category of a super-Earth planet—and would orbit approximately 1.5 AU from its star. It would also take the planet approximately five Earth years to make one orbit around its star. They note that such a long distance from a cooling star would likely mean very cold temperatures on the exoplanet—perhaps as cold as -234 degrees C.

With its three planets orbiting two suns, Kepler-47 is the only known multi-planet circumbinary system. Two new planets found.Jerome Orosz; William Welsh

ν Ophiuchi is being orbited by two brown dwarfs with an orbital period of approximately 530 and 3,185 days, which puts them in a 6:1 resonant configuration. Prof. Dr. Andreas Quirrenbach and his team at the Königstuhl State Observatory

Planet deserts

December

Scientists noticed that there were lots of these planets about the size of or just larger than Earth, but there was a steep cutoff before planets reached the size of Neptune. "This is a cliff edge in the data, and it's quite dramatic," said University of Chicago planetary scientist Edwin Kite. "What we have been puzzling over is why planets would tend to stop growing beyond about three times Earth's size." In a paper published Dec. 17 in Astrophysical Journal Letters, Kite and colleagues at Washington University, Stanford University, and Penn State University offer an innovative explanation for this drop-off: The oceans of magma on the surface of these planets readily absorb their atmospheres once planets reach about three times the size of Earth. Kite, who studies the history of Mars and the climates of other worlds, was well-positioned to study the question. He thought the answer might hinge on a little-studied aspect of such exoplanets. Most of the planets slightly smaller than the drop-off size are thought to have oceans of magma on their surfaces—great seas of molten rock like the ones that once covered Earth. But instead of solidifying as ours did, these are kept hot by a thick blanket of hydrogen-rich atmosphere. "So far, almost all models we have ignore this magma, treating it as chemically inert, but liquid rock is almost as runny as water and very reactive," said Kite, an assistant professor in the Department of Geophysical Sciences. The question Kite and his colleagues considered was whether, as the planets acquired more hydrogen, the ocean might begin to "eat" the sky. In this scenario, as the planet acquires more gas, it piles up in the atmosphere, and the pressure at the bottom where the atmosphere meets the magma starts to build. At first, the magma takes up the added gas at a steady rate, but as the pressure rises, the hydrogen starts to dissolve much more readily into the magma. "Not only that, but the little bit of the added gas that stays in the atmosphere raises the atmospheric pressure, and thus an even greater fraction of later-arriving gas will dissolve into the magma," Kite said. Thus the planet's growth stalls out before it reaches the size of Neptune. (Because the majority of the volume of these planets is in the atmosphere, shrinking the atmosphere shrinks the planets.) The authors call this the "fugacity crisis," after the term that measures how much more readily a gas dissolves into a mixture than what would be expected based on pressure. The theory fits well with existing observations, Kite said. There are also several markers that astronomers could look for in future. For example, if the theory is correct, planets with magma oceans that are cold enough to have crystallized on the surface should display different profiles, since this would prevent the ocean from absorbing so much hydrogen. Ongoing and future surveys from TESS and other telescopes should give astronomers more data with which to work.

May

An exoplanet smaller than Neptune with its own atmosphere has been discovered in the Neptunian Desert. NGTS is situated at the European Southern Observatory's Paranal Observatory in the heart of the Atacama Desert, Chile. It is a collaboration between UK Universities Warwick, Leicester, Cambridge, and Queen's University Belfast, together with Observatoire de Genève, DLR Berlin and Universidad de Chile. NGTS-4b, also nick-named 'The Forbidden Planet' by researchers, is a planet smaller than Neptune but three times the size of Earth. It has a mass of 20 Earth masses, and a radius 20% smaller than Neptune, and is 1000 degrees Celsius. It orbits around the star in only 1.3 days—the equivalent of Earth's orbit around the sun of one year. It is the first exoplanet of its kind to have been found in the Neptunian Desert. The Neptunian Desert is the region close to stars where no Neptune-sized planets are found. This area receives strong irradiation from the star, meaning the planets do not retain their gaseous atmosphere as they evaporate leaving just a rocky core. However NGTS-4b still has its atmosphere of gas. Researchers believe the planet may have moved into the Neptunian Desert recently, in the last one million years, or it was very big and the atmosphere is still evaporating.

Planet definition

November

In terms of mass, 13 Jupiter masses is a good upper limit. But when it comes to large planets, the most massive ones aren't actually the largest in size. For example, Jupiter is three times the mass of Saturn but is less than 20 percent larger by volume. Going back to our model of hydrostatic equilibrium, the most massive planets are actually smaller than Jupiter in size. A few years ago Jingjing Chen and David Kipping looked at how the size of planets can vary depending on their mass. They found that there is a transition point between Neptune-type worlds where more mass tends to increase their size and Jupiter-type worlds where more mass tends to simply compress the gas more. That critical point is about half the mass of Jupiter, so the largest planets should have around that mass. This agrees with observation. The largest confirmed exoplanet is WASP-17b. It is roughly twice the size of Jupiter but has only 49 percent of Jupiter's mass. Of course, there are other factors that come into play, such as composition and temperature. The largest known exoplanets tend to be hot Jupiters orbiting close to their star. This means they are much warmer and less dense than a cold jovian planet like Jupiter. Jupiter also has a dense rocky core, which means it is smaller than it would be if it were made only of hydrogen and helium. But even taking these factors into account, jovian planets are clearly both the largest and most massive planets that can exist. Jupiter isn't the largest planet in the universe, but it is one of the giants.

September

The star itself is a red dwarf, about 30 light years away, with a luminosity less than 0.2% that of the sun. It has around 12% of the sun's mass and 14% of its radius. Such cool, dim stars are in fact the most common stars in the galaxy, but only one in ten of the known exoplanets have been found to orbit red dwarfs. That makes the new discovery stand out is that the planet, dubbed GJ3512b, is a gas giant in a 204-day elliptical orbit. The planet has a mass of at least half that of Jupiter and its diameter is likely to be around 70% that of the star it orbits. It is therefore one of the largest planets known to be orbiting such a small star in such a wide orbit—and this poses a problem for understanding how it formed. An alternative scenario is likely to have happened in the case of GJ3512b—and potentially many other planetary systems out there. Here, it seems the planet may have formed by direct fragmentation of the protoplanetary disc. That means part of the disc collapsed and condensed (changing from gas to a liquid and thereafter solid) into a large body, without the need to build up by accumulation of smaller rocks. This is similar to the way in which stars themselves normally form. The team behind the new study report further evidence for this formation route from hints of a second giant exoplanet in the system (tentatively called GJ3512c) with an orbital period in excess of 1,400 days. This might also explain the unusually eccentric orbit of GJ3512b, which may have resulted from interactions between the two planets soon after the planets formed. This process would have ejected a third planet from the system. And if three large planets once existed around such a small star, the only way they could have formed is by direct fragmentation of the disc.

Phosphorous

December

So how were we so lucky to evolve on a planet with plenty of oxygen? The history of Earth's oceans and atmosphere suggests that the rise to present-day levels of O₂ was pretty difficult. The current consensus is that Earth underwent a three-step rise in atmospheric and oceanic oxygen levels, the first being called the "Great Oxidation Event" at around 2.4 billion years ago. After that came the "Neoproterozoic Oxygenation Event" around 800 million years ago, and then finally the "Paleozoic Oxygenation Event" about 400 million years ago, when oxygen levels on Earth reached their modern peak of 21%. What happened during these three periods to increase oxygen levels is a matter for debate. One idea is that new organisms "bioengineered" the planet, restructuring the atmosphere and oceans through either their metabolisms or their lifestyles. For example, the rise of land plants roughly 400 million years ago could have increased oxygen in the atmosphere through land-based photosynthesis, taking over from photosynthetic bacteria in the ocean which have been the main oxygen producers for most of Earth's history. Alternatively, plate tectonic changes or gigantic volcanic eruptions have also been linked to the Earth's oxygenation events. This event-based history of how oxygen came to be so plentiful on Earth implies that we're very fortunate to be living on a high-oxygen world. If one volcanic eruption hadn't happened, or a certain type of organism hadn't evolved, then oxygen might have stalled at low levels. But our latest research suggests that this isn't the case. We created a computer model of the Earth's carbon, oxygen and phosphorus cycles and found that the oxygen transitions can be explained by the inherent dynamics of our planet and likely didn't require any miraculous events. These stromatolites are the earliest fossil evidence of photosynthetic life. Shark Bay, Australia. Credit: Paul Harrison/Wikipedia, CC BY-SA One thing we think is missing from theories about Earth's oxygenation is phosphorus. This nutrient is very important for photosynthetic bacteria and algae in the ocean. How much marine phosphorous there is will ultimately control how much oxygen is produced on Earth. This is still true today—and has been so since the evolution of photosynthetic microbes some three billion years ago. Photosynthesis in the ocean depends on phosphorus, but high phosphate levels also drive consumption of oxygen in the deep ocean through a process called eutrophication. When photosynthetic microbes die, they decompose, which consumes oxygen from the water. As oxygen levels fall, sediments tend to release even more phosphorus. This feedback loop rapidly removes oxygen. This meant that oxygen levels in the oceans were able to change rapidly, but they were buffered over long timescales by another process involving the Earth's mantle. Eutrophication can lead to an algal bloom. As microbes die and decompose, oxygen is stripped from the water. Credit: Pumidol/Shutterstock Throughout Earth's history, volcanic activity has released gases that react with and remove oxygen from the atmosphere. These gas fluxes have subsided over time due to Earth's mantle cooling, and our computer model suggests this slow reduction along with the initial evolution of photosynthetic life was all that was necessary to produce a series of step-change increases in oxygen levels. These stepped increases bear a clear resemblance to the three-step rise in oxygen that has occurred throughout Earth's history. The model also supports our current understanding of ocean oxygenation, which appears to have involved numerous cycles of oxygenation and deoxygenation before the oceans became resiliently oxygenated as they are today. What is really exciting about all of this is that the oxygenation pattern can be created without the need for difficult and complex evolutionary leaps forward, or circumstantial catastrophic volcanic or tectonic events. So it appears that Earth's oxygenation may have been inescapable once photosynthesis had evolved—and the chances of high oxygen worlds existing elsewhere could be much higher.#

Phosphine is among the stinkiest, most toxic gases on Earth, found in some of the foulest of places, including penguin dung heaps, the depths of swamps and bogs, and even in the bowels of some badgers and fish. This putrid "swamp gas" is also highly flammable and reactive with particles in our atmosphere. Most life on Earth, specifically all aerobic, oxygen-breathing life, wants nothing to do with phosphine, neither producing it nor relying on it for survival. Now MIT researchers have found that phosphine is produced by another, less abundant life form: anaerobic organisms, such as bacteria and microbes, that don't require oxygen to thrive. The team found that phosphine cannot be produced in any other way except by these extreme, oxygen-averse organisms, making phosphine a pure biosignature—a sign of life (at least of a certain kind). In a paper recently published in the journal Astrobiology, the researchers report that if phosphine were produced in quantities similar to methane on Earth, the gas would generate a signature pattern of light in a planet's atmosphere. This pattern would be clear enough to detect from as far as 16 light years away by a telescope such as the planned James Webb Space Telescope. If phosphine is detected from a rocky planet, it would be an unmistakable sign of extraterrestrial life.

Titan

December

Liming Li, a physics professor at UH and corresponding author on the paper, said it takes Saturn about 29 Earth years to complete its orbit. Still, he said, learning more about the energy budget of Titan can add to understanding of climate change on Earth. Previous studies have detected a small energy imbalance on Earth, he said. "Earth's small energy imbalance has significant effects on its global warming and climate change," he said. "We expect that the dynamically-varying energy budget and the possible energy imbalance have important impacts on the weather and climate systems on Titan. The researchers used data collected from the Cassini mission between 2004 and 2017—the equivalent of about half an Earth year for Saturn and Titan, or portions of three seasons. That data provided the first opportunity to systematically examine the seasonal variations of Titan. While previous studies have suggested Titan's energy budget is in balance, the researchers determined that both emitted thermal energy and absorbed solar energy decreased over the 14-year period studied. But thermal emissions dropped less—about 6.8%, compared with an 18.6% drop in solar energy at Titan. That varied between the northern and southern atmospheres of Titan, as well as depending on the moon's distance from the sun during its orbit. The findings suggest the distance between the sun and Earth may play a role in Earth's energy balance, said Xun Jiang, professor of atmospheric science at UH. "Such a mechanism has not been examined for Earth's energy imbalance," Jiang said, noting that future work will compare Titan and Earth's energy budgets in order to better understand the climate systems on each. Two scenarios resulted in bubbles. At temperatures below 86 degrees Kelvin, ethane layered on top of nitrogen-rich methane, no matter what order they were poured into the petri dish. As the temperature warmed, the methane underneath began to foam and when the layers dissolved, bubbles reached the surface.

In the new study published in AGU's journal Geophysical Research Letters, researchers simulated Titan's lakes in a pressurized chamber. They found the right combination of methane, ethane and nitrogen crucial for bubbles to form. Under conditions most like those on Titan, the researchers found ethane had to flow into pools of methane to produce vigorous bubbles. It is possible these bubble outbreaks are strong enough to shape river deltas in bodies of liquid on the moon, according to the new research. Explaining how bubbles form in Titan's lakes now allows scientists to begin probing fundamental questions about how liquids behave on the moon. Of all the bodies in our solar system, few are more Earth-like than Titan, and it is one of the few places scientists think might have conditions necessary for extraterrestrial life. The results also hint at scenarios an exploratory submarine might face in Titan's lakes, if the spacecraft were to give off heat and potentially spark an explosion of bubbles. "The more we learn about Titan, the more we learn that we can't ignore the lakes," said Kendra Farnsworth, a planetary scientist at the University of Arkansas in Fayetteville and lead author of the new study. "And we find fun things like bubbles. Maybe a little bit more violent than we'd expected, but definitely fun to watch." Previous work found nitrogen gas from Titan's atmosphere could readily dissolve into cold pools with high concentrations of methane—like when carbon dioxide dissolves into soda. Upon heating, the liquid released nitrogen gas in the form of fizzing bubbles. But these earlier experiments didn't fully mimic the natural environment on Titan. They also didn't explain what conditions could make the lakes foam, although researchers suspected it happens during heavy rainfall or when a stream flows into a lake. "Titan's lakes have very interesting dynamics," Farnsworth said. "They're not just static bodies of liquid." Two scenarios resulted in bubbles. At temperatures below 86 degrees Kelvin, ethane layered on top of nitrogen-rich methane, no matter what order they were poured into the petri dish. As the temperature warmed, the methane underneath began to foam and when the layers dissolved, bubbles reached the surface.

November

Titan has an active methane-based hydrologic cycle1 that has shaped a complex geologic landscape2, making its surface one of most geologically diverse in the Solar System. Despite the differences in materials, temperatures and gravity fields between Earth and Titan, many of their surface features are similar and can be interpreted as products of the same geologic processes3. However, Titan’s thick and hazy atmosphere has hindered the identification of its geologic features at visible wavelengths and the study of its surface composition4. Here we identify and map the major geological units on Titan’s surface using radar and infrared data from the Cassini orbiter spacecraft. Correlations between datasets enabled us to produce a global map even where datasets were incomplete. The spatial and superposition relations between major geological units reveals the likely temporal evolution of the landscape and provides insight into the interacting processes driving its evolution. We extract the relative dating of the various geological units by observing their spatial superposition in order to get information on the temporal evolution of the landscape. The dunes and lakes are relatively young, whereas the hummocky or mountainous terrains are the oldest on Titan. Our results also show that Titan’s surface is dominated by sedimentary or depositional processes with a clear latitudinal variation, with dunes at the equator, plains at mid-latitudes and labyrinth terrains and lakes at the poles.

October

A trio of researchers with the University of Hawaii has developed a new theory to explain how the dunes on Saturn's largest moon, Titan, may have formed. In their paper published in the journal Science Advances, Matthew Abplanalp, Robert Frigge and Ralf Kaiser suggest that rather than forming from rainfall, the dunes have formed on the moon's surface. theories that such organic molecules fall from the atmosphere and form the dunes that cover part of the equatorial region on the moon's surface. In this new effort, Abplanalp, Frigge and Kaiser suggest that the dunes may have arisen another way—via cosmic rays striking acetylene ice, inciting reactions that lead to the formation of the materials that make up the dunes. The researchers tested their theory by creating batches of acetylene ice in their lab and then bombarding it with radiation similar to that experienced by Titan. They then heated the ice until it sublimated, leaving behind material made of organic molecules similar to those believed to form the dunes on Titan. In so doing, they found that the process could produce phenanthrene in as little as 100 years; other molecules would take longer.

September

Titan's lakes show liquid methane dissolving the moon's bedrock of ice and solid organic compounds, carving reservoirs that fill with the liquid. This may be the origin of a type of lake on Titan that has sharp boundaries. On Earth, bodies of water that formed similarly, by dissolving surrounding limestone, are known as karstic lakes. The new, alternative models for some of the smaller lakes (tens of miles across) turns that theory upside down: It proposes pockets of liquid nitrogen in Titan's crust warmed, turning into explosive gas that blew out craters, which then filled with liquid methane. The new theory explains why some of the smaller lakes near Titan's north pole, like Winnipeg Lacus, appear in radar imaging to have very steep rims that tower above sea level—rims difficult to explain with the karstic model.

July

Most of Titan's smaller lakes are characterized as sharp-edged depressions, either empty or full, with relatively flat floors, depths of up to 600 m, and steep, narrow outer rims roughly 1 km in width. Some lakes, however, are surrounded by ramparts: ring-shaped mounds that extend for tens of km from a lake's shoreline. Unlike rims, these ramparts totally enclose their host lake. "The formation of Titan's lakes, and their surrounding features, remains an open question," says Anezina Solomonidou, an ESA research fellow at the European Space Astronomy Centre (ESAC) near Madrid, Spain, and lead author of a new study into Titan's ramparts. "Ramparts may hold important clues about how the lake-filled polar regions of Titan became what we see today. Previous research revealed their existence, but how did they for" Solomonidou and her collaborators combined spectral and radar data from Cassini for the first time to explore five regions near Titan's north pole with filled lakes and raised ramparts, and three empty lakes from a nearby region. The lakes ranged from 30 to 670 square km in size, and were entirely surrounded by 200 to 300 m-high ramparts that sprawled outwards from the lake perimeters for up to 30 km. June

Titan's lakes are filled with liquid hydrocarbons. Previous research using images and data gathered during the Cassini mission has shown that lakes in the moon's dry regions near the equator contain signs of evaporated material left behind, like rings on a bathtub. Scientists re-creating Titan-esque conditions in their laboratory have discovered new compounds and minerals not found on Earth, including a co-crystal made of solid acetylene and butane. The first things to drop out of their Titan hydrocarbon soup were benzene crystals. But Titan benzene held a surprise: The molecules rearranged themselves and allowed ethane molecules inside, creating a co-crystal.

April

a long ice feature that wraps nearly half way around Titan. Griffith, a professor in the UA Lunar and Planetary Laboratory, is the lead author on the paper published today in Nature Astronomy. Titan's nothern smaller lakes are 100 m deep, and mostly methane, as opposed to southern lakes, which are equally methane and ethane.

There is no obvious source of methane, except from the evaporation of methane from the polar lakes. But Titan's lakes contain only one-third of the methane in Titan's atmosphere and will be exhausted soon by geological time scales. One theory is that the methane could be supplied by subsurface reservoirs that vent methane into the atmosphere. Prior studies of Titan indicate the presence of a singular region called Sotra, which looks like cryo-volcano, with icy flow features.

a linear ice corridor that wraps around 40 percent of Titan's circumference. "This icy corridor is puzzling, because it doesn't correlate with any surface features nor measurements of the subsurface,"

"Given that our study and past work indicate that Titan is currently not volcanically active, the trace of the corridor is likely a vestige of the past. We detect this feature on steep slopes, but not on all slopes. This suggests that the icy corridor is currently eroding, potentially unveiling presence of ice and organic strata."

Jan Dr. Kelly Miller, research scientist in SwRI's Space Science and Engineering DivisionTo study the Titan mystery, Miller combined existing data from organic material found in meteorites with previous thermal models of the moon's interior to see how much gaseous material could be produced and whether it was comparable to the atmosphere now. Following the standard rule of, "If you cook something, it will produce gases," Miller found that approximately half of the nitrogen atmosphere, and potentially all of the methane, could result from the "cooking" of these organics that were incorporated into Titan at its very beginning.

jan

Dhingra and her colleagues identified a reflective feature near Titan's north pole on an image taken June 7, 2016, by Cassini's near-infrared instrument, the Visual and Infrared Mapping Spectrometer. The reflective feature covered approximately 46,332 square miles, roughly half the size of the Great Lakes, and did not appear on images from previous and subsequent Cassini passes.

Analyses of the short-term reflective feature suggested it likely resulted from sunlight reflecting off a wet surface. The study attributes the reflection to a methane rainfall event, followed by a probable period of evaporation.

case of the missing clouds

The maps combine data from the multitude of different observations made under a wide variety of illumination and viewing conditions over the course of the mission, stitched together in a seamless mosaic to provide the best representation of Titan's surface to date. dunes brown ice purple

Star birth and death

December

Working with a team that includes UT Austin undergraduate and graduate students as well as colleagues from Princeton University, the Carnegie Observatories, and the University of California, Berkeley, Hawkins focused on 25 widely spaced binary stars identified by the Gaia satellite. Each such binary contains two stars that were born together billions of years ago, out of a single collapsing cloud of gas and dust. Using the 2.7-meter Harlan J. Smith Telescope at McDonald Observatory, Hawkins probed the detailed chemical compositions of all 50 stars in these binary systems to a greater depth than any previous studies. His results demonstrated that stars born together show chemical compositions that are virtually identical—many times more so than same-type stars chosen at random. These results have implications far beyond just understanding binary stars, Hawkins said. The study serves as a proof-of-concept for the idea of "chemical tagging"—using the chemical compositions of stars spread throughout the galaxy to figure out which stars formed together initially. Astronomers know that vast numbers of stars are born in giant clouds of gas and dust often referred to as stellar nurseries. During the course of millions or billions of years, though, Hawkins says, these "loose assemblies of stars that form together get dispersed over time."

Researchers have discovered gigantic clouds of gaseous carbon spanning more than a radius of 30,000 light-years around young galaxies using the Atacama Large Millimeter/submillimeter Array (ALMA). This is the first confirmation that carbon atoms produced inside of stars in the early universe have spread beyond galaxies. No theoretical studies have predicted such huge carbon cocoons around growing galaxies, which raises questions about our current understanding of cosmic evolution. "We examined the ALMA Science Archive thoroughly and collected all the data that contain radio signals from carbon ions in galaxies in the early universe, only one billion years after the Big Bang," says Seiji Fujimoto, the lead author of the research paper who is an astronomer at the University of Copenhagen, and a former Ph.D. student at the University of Tokyo. "By combining all the data, we achieved unprecedented sensitivity. To obtain a dataset of the same quality with one observation would take 20 times longer than typical ALMA observations, which is almost impossible to achieve." Heavy elements such as carbon and oxygen did not exist in the universe at the time of the Big Bang. They were formed later by nuclear fusion in stars. However, it is not yet understood how these elements spread throughout the universe. Astronomers have found heavy elements inside baby galaxies but not beyond those galaxies, due to the limited sensitivity of their telescopes. This research team summed the faint signals stored in the data archive and pushed the limits. "The gaseous carbon clouds are almost five times larger than the distribution of stars in the galaxies, as observed with the Hubble Space Telescope," explains Masami Ouchi, a professor at the National Astronomical Observatory of Japan and the University of Tokyo. "We spotted diffuse but huge clouds floating in the coal-black universe." Then, how were the carbon cocoons formed? "Supernova explosions at the final stage of stellar life expel heavy elements formed in the stars," says Professor Rob Ivison, the Director for Science at the European Southern Observatory. "Energetic jets and radiation from supermassive black holes in the centers of the galaxies could also help transport carbon outside of the galaxies and finally to throughout the universe. We are witnessing this ongoing diffusion process, the earliest environmental pollution in the universe." The research team notes that at present theoretical models are unable to explain such large carbon clouds around young galaxies, probably indicating that some new physical process must be incorporated into cosmological simulations. "Young galaxies seem to eject an amount of carbon-rich gas far exceeding our expectation," says Andrea Ferrara, a professor at Scuola Normale Superiore di Pisa.

NASA's Fermi Gamma-ray Space Telescope has discovered a faint but sprawling glow of high-energy light around a nearby pulsar. If visible to the human eye, this gamma-ray "halo" would appear about 40 times bigger in the sky than a full Moon. This structure may provide the solution to a long-standing mystery about the amount of antimatter in our neighborhood. "Our analysis suggests that this same pulsar could be responsible for a decade-long puzzle about why one type of cosmic particle is unusually abundant near Earth," said Mattia Di Mauro, an astrophysicist at the Catholic University of America in Washington and NASA's Goddard Space Flight Center in Greenbelt, Maryland. "These are positrons, the antimatter version of electrons, coming from somewhere beyond the solar system." A neutron star is the crushed core left behind when a star much more massive than the Sun runs out of fuel, collapses under its own weight and explodes as a supernova. We see some neutron stars as pulsars, rapidly spinning objects emitting beams of light that, much like a lighthouse, regularly sweep across our line of sight. Geminga (pronounced geh-MING-ga), discovered in 1972 by NASA's Small Astronomy Satellite 2, is among the brightest pulsars in gamma rays. It is located about 800 light-years away in the constellation Gemini. Geminga's name is both a play on the phrase "Gemini gamma-ray source" and the expression "it's not there"— referring to astronomers' inability to find the object at other energies—in the dialect of Milan, Italy. Geminga was finally identified in March 1991, when flickering X-rays picked up by Germany's ROSAT mission revealed the source to be a pulsar spinning 4.2 times a second. A pulsar naturally surrounds itself with a cloud of electrons and positrons. This is because the neutron star's intense magnetic field pulls the particles from the pulsar's surface and accelerates them to nearly the speed of light. Electrons and positrons are among the speedy particles known as cosmic rays, which originate beyond the solar system. Because cosmic ray particles carry an electrical charge, their paths become scrambled when they encounter magnetic fields on their journey to Earth. This means astronomers cannot directly track them back to their sources. For the past decade, cosmic ray measurements by Fermi, NASA's Alpha Magnetic Spectrometer (AMS-02) aboard the International Space Station, and other space experiments near Earth have seen more positrons at high energies than scientists expected. Nearby pulsars like Geminga were prime suspects. Then, in 2017, scientists with the High-Altitude Water Cherenkov Gamma-ray Observatory (HAWC) near Puebla, Mexico, confirmed earlier ground-based detections of a small gamma-ray halo around Geminga. They observed this structure at energies from 5 to 40 trillion electron volts—light with trillions of times more energy than our eyes can see. Scientists think this emission arises when accelerated electrons and positrons collide with nearby starlight. The collision boosts the light up to much higher energies. Based on the size of the halo, the HAWC team concluded that Geminga positrons at these energies only rarely reach Earth. If true, it would mean that the observed positron excess must have a more exotic explanation. But interest in a pulsar origin continued, and Geminga was front and center. Di Mauro led an analysis of a decade of Geminga gamma-ray data acquired by Fermi's Large Area Telescope (LAT), which observes lower-energy light than HAWC. Particles traveling near light speed can interact with starlight and boost it to gamma-ray energies. This animation shows the process, known as inverse Compton scattering. When light ranging from microwave to ultraviolet wavelengths collides with a fast-moving particle, the interaction boosts it to gamma rays, the most energetic form of light. "To study the halo, we had to subtract out all other sourcesf gamma rays, including diffuse light produced by cosmic ray collisions with interstellar gas clouds," said co-author Silvia Manconi, a postdoctoral researcher at RWTH Aachen University in Germany. "We explored the data using 10 different models of interstellar emission." What remained when these sources were removed was a vast, oblong glow spanning some 20 degrees in the sky at an energy of 10 billion electron volts (GeV). That's similar to the size of the famous Big Dipper star pattern—and the halo is even bigger at lower energies. "Lower-energy particles travel much farther from the pulsar before they run into starlight, transfer part of their energy to it, and boost the light to gamma rays. This is why the gamma-ray emission covers a larger area at lower energies ," explained co-author Fiorenza Donato at the Italian National Institute of Nuclear Physics and the University of Turin. "Also, Geminga's halo is elongated partly because of the pulsar's motion through space." The team determined that the Fermi LAT data were compatible with the earlier HAWC observations. Geminga alone could be responsible for as much as 20% of the high-energy positrons seen by the AMS-02 experiment. Extrapolating this to the cumulative emission from all pulsars in our galaxy, the scientists say it's clear that pulsars remain the best explanation for the positron excess.

October

As with many supernova remnants, the Tycho supernova remnant, as it's known today (or "Tycho," for short), glows brightly in X-ray light because shock waves—similar to sonic booms from supersonic aircraft—generated by the stellar explosion heat the stellar debris up to millions of degrees. In its two decades of operation, NASA's Chandra X-ray Observatory has captured unparalleled X-ray images of many supernova remnants. Chandra reveals an intriguing pattern of bright clumps and fainter areas in Tycho. What caused this thicket of knots in the aftermath of this explosion? Did the explosion itself cause this clumpiness, or was it something that happened afterward? This latest image of Tycho from Chandra is providing clues. To emphasize the clumps in the image and the three-dimensional nature of Tycho, scientists selected two narrow ranges of X-ray energies to isolate material (silicon, colored red) moving away from Earth, and moving towards us (also silicon, colored blue). The other colors in the image (yellow, green, blue-green, orange and purple) show a broad range of different energies and elements, and a mixture of directions of motion. In this new composite image, Chandra's X-ray data have been combined with an optical image of the stars in the same field of view from the Digitized Sky Survey. By comparing the Chandra image of Tycho to two different computer simulations, researchers were able to test their ideas against actual data. One of the simulations began with clumpy debris from the explosion. The other started with smooth debris from the explosion and then the clumpiness appeared afterwards as the supernova remnant evolved and tiny irregularities were magnified. A statistical analysis using a technique that is sensitive to the number and size of clumps and holes in images was then used. Comparing results for the Chandra and simulated images, scientists found that the Tycho supernova remnant strongly resembles a scenario in which the clumps came from the explosion itself. While scientists are not sure how, one possibility is that star's explosion had multiple ignition points, like dynamite sticks being set off simultaneously in different locations.

August

A renegade star exploding in a distant galaxy has forced astronomers to set aside decades of research and focus on a new breed of supernova that can utterly annihilate its parent star—leaving no remnant behind. The signature event, something astronomers had never witnessed before, may represent the way in which the most massive stars in the Universe, including the first stars, die. The European Space Agency's (ESA) Gaia satellite first noticed the supernova, known as SN 2016iet, on November 14, 2016. Three years of intensive follow-up observations with a variety of telescopes, including the Gemini North telescope and its Multi-Object Spectrograph on Maunakea in Hawaiʻi, provided crucial perspectives on the object's distance and composition. "The Gemini data provided a deeper look at the supernova than any of our other observations," said Edo Berger of the Harvard-Smithsonian Center for Astrophysics and a member of the investigation's team. "This allowed us to study SN 2016iet more than 800 days after its discovery, when it had dimmed to one-hundredth of its peak brightness." SN 2016iet has a multitude of oddities, including its incredibly long duration, large energy, unusual chemical fingerprints, and environment poor in heavier elements—for which no obvious analogues exist in the astronomical literature. it began its life as a star with about 200 times the mass of our Sun—making it one of the most massive and powerful single star explosions ever observed. Growing evidence suggests the first stars born in the Universe may have been just as massive. Astronomers predicted that if such behemoths retain their mass throughout their brief life (a few million years), they will die as pair-instability supernovae, which gets its name from matter-antimatter pairs formed in the explosion.

In a paper published in the journal Monthly Notices of the Royal Astronomical Society: Letters, researchers led by Dr. Thomas Nordlander of the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3-D) confirm the existence of an ultra-metal-poor red giant star, located in the halo of the Milky Way, on the other side of the Galaxy about 35,000 light-years from Earth. Spectroscopic analysis indicated that the star had an iron content of just one part per 50 billion. "That's like one drop of water in an Olympic swimming pool," explains Dr. Nordlander. "This incredibly anaemic star, which likely formed just a few hundred million years after the Big Bang, has iron levels 1.5 million times lower than that of the Sun." Its diminutive iron content is enough to place the star—formally dubbed SMSS J160540.18–144323.1—into the record books, but it is what that low level implies about its origin that has the astronomers really excited. The very first stars in the Universe are thought to have consisted of only hydrogen and helium, along with traces of lithium. These elements were created in the immediate aftermath of the Big Bang, while all heavier elements have emerged from the heat and pressure of cataclysmic supernovae—titanic explosions of stars. Stars like the Sun that are rich in heavy element therefore contain material from many generations of stars exploding as supernovae.

July

Iron in interstellar environments should also be common, but astrophysicists detect only low levels of the gaseous kind. This implies that the missing iron exists in some kind of solid form or molecular state, yet identifying its hiding place has remained elusive for decades. June team of cosmochemists at Arizona State University, with support from the W.M. Keck Foundation, now claims that the mystery is simpler than it seems. The iron isn't really missing, they say. Instead it's hiding in plain sight. The iron has combined with carbon molecules to form molecular chains called iron pseudocarbynes. The spectra of these chains are identical with the much more common chains of carbon molecules, long known to be abundant in interstellar space. We are proposing a new class of molecules that are likely to be widespread in the interstellar medium," said Pilarasetty Tarakeshwar, research associate professor in ASU's School of Molecular Sciences. we found that they have spectroscopic signatures nearly identical to carbon-chain molecules without any iron."

At the annual meeting of the American Astronomical Society in St. Louis, Missouri, Allison Kirkpatrick, assistant professor of physics and astronomy at the University of Kansas, will announce her discovery of "cold quasars"—galaxies featuring an abundance of cold gas that still can produce new stars despite having a quasar at the center—a breakthrough finding that overturns assumptions about the maturation of galaxies and may represent a phase of every galaxy's lifecycle that was unknown until now. These jets essentially choke off the gas supply of the galaxy, so no more gas can fall on to the galaxy and form new stars. After a galaxy has stopped forming stars, we say it's a passive dead galaxy." in her survey represented a brief period yet to be recognized in the end-phases of a galaxy's lifespan—in terms of a human life, the fleeting "cold quasar" phase may something akin to a galaxy's retirement party.

Astronomers using the Nobeyama Radio Obeservatory (NRO) 45-meter telescope found that high-density gas, the material for stars, accounts for only 3 percent of the total mass of gas distributed in the Milky Way. This result provides key information for understanding the unexpectedly low production rate of stars. Stars are born in gas clouds. The high-density gas pockets form in the extended, low-density gas clouds, and stars form in the very dense gas cores which evolve within the high-density gas. However, observations of distant galaxies detected 1000 times fewer stars than the production value expected from the total amount of low-density gas. To interpret the discrepancy, observations which detect both of the high-density and low-density gas with high-spatial resolution and wide area coverage were needed. However, such observations are difficult, because the high-density gas structures are dozens of times smaller than the low-density gas structures. The TNG50 simulation, which has just been published, manages to avoid this trade-off. For the first time, it combines the idea of a large-scale cosmological simulation—a Universe in a box—with the computational resolution of "zoom" simulations, at a level of detail that had previously only been possible for studies of individual galaxies. In a simulated cube of space that is more than 230 million light-years across, TNG50 can discern physical phenomena that occur on scales one million times smaller, tracing the simultaneous evolution of thousands of galaxies over 13.8 billion years of cosmic history. It does so with more than 20 billion particles representing dark (invisible) matter, stars, cosmic gas, magnetic fields, and supermassive black holes. The calculation itself required 16,000 cores on the Hazel Hen supercomputer in Stuttgart, working together, 24/7, for more than a year—the equivalent of fifteen thousand years on a single processor, making it one of the most demanding astrophysical computations to date. As these galaxies flatten out, researchers found another emergent phenomenon, involving the high-speed outflows and winds of gas flowing out of galaxies. This launched as a result of the explosions of massive stars (supernovae) and activity from supermassive black holes found at the heart of galaxies. Galactic gaseous outflows are initially also chaotic and flow away in all directions, but over time, they begin to become more focused along a path of least resistance. esearchers have seen how the well-ordered, rapidly rotating disc galaxies (which are common in our nearby Universe) emerge from chaotic, disorganised, and highly turbulent clouds of gas at earlier epochs. As the gas settles down, newborn stars are typically found on more and more circular orbits, eventually forming large spiral galaxies—galactic carousels. In the late universe, flows out of galaxies take the form of two cones, emerging in opposite directions—like two ice cream cones placed tip to tip, with the galaxy swirling at the centre. These flows of material slow down as they attempt to leave the gravitational well of the galaxy's halo of invisible—or dark—matter, and can eventually stall and fall back, forming a galactic fountain of recycled gas. This process redistributes gas from the centre of a galaxy to its outskirts, further accelerating the transformation of the galaxy itself into a thin disc: galactic structure shapes galactic fountains, and vice versa.

These globular clusters are thought to have formed shortly after the birth of the universe about 13,800 million years ago, at the same time or even before the first galaxies formed. Since then, they have remained largely unchanged apart from the ageing of all their stars and the gradual death of most of the remaining stars. Thomas Broadhurst, the Ikerbasque Research Professor at the UPV/EHU's Department of Theoretical Physics and History of Science, explained that "it is not fully understood why the brightest galaxies form in the centre of the galaxy clusters. The fact that they contain thousands of old globular clusters may be a point to take into consideration." A study led by Dr. Lim of the University of Hong Kong and published by the prestigious journal Nature Astronomy, and in which Broadhurst collaborated, has found unexpected answers to the origin of some globular clusters located around the giant galaxies at the centre of galaxy clusters: "We discovered that thousands of new globular clusters have been forming over the last billion years out of a cool gas in the giant galaxy located in the centre of the Perseus galaxy cluster," explained Prof Broadhurst. The younger globular clusters are closely associated with, and therefore formed from, a complex network of cool gas that extends to the outer reaches of the giant galaxy. This network of cool gas precipitates from the hot gas that infuses the entire Perseus galaxy cluster; in fact, the gas concentrates in the centre allowing it to cool faster and that leads to the creation of globular clusters. Once formed, these infant globular clusters do not remain in the network of cool gas and rain inwards onto the giant galaxy like raindrops falling from the clouds. "So," explained Broadhurst, "one could expect that the central galaxies of these clusters will grow in brightness over cosmic time as a result of the rain of globular clusters they receive from the gas that surrounds them". June

The Milky Way Project: Probing Star Formation with a New Yellowball Catalog presents a study of 518 infant star-forming regions known as "Yellowballs," named for their appearance in Spitzer Space Telescope images, drawn from a catalog made possible by the efforts of citizen scientists. Complex organic molecules known as Polycyclic Aromatic Hydrocarbons (or PAHs) show up as green in the images, and very small dust particles as red—where the two overlap completely, you get yellow. YBs are larger than our solar system, but most are considerably smaller than the typical distance between stars, and yet some of them may eventually produce thousands of stars. The new catalog contains the positions and sizes of YBs across a large swath of the Milky Way,

May

Type Ia supernovae originate from the thermonuclear explosion of a white dwarf that is part of a binary system. But what exactly triggers the explosion of the white dwarf—the dead core left after a Sun-like star exhausts its nuclear fuel—is a great puzzle. A prevailing idea is that, the white dwarf gains matter from its companion star, a process that may eventually trigger the explosion, but whether this is the correct theory has been hotly debated for decades.

This led the research team behind this paper to begin a major survey of Type Ia supernovae—called 100IAS—that was launched when Kollmeier was discussing the origin of these supernovae with study co-authors Subo Dong of Peking University and Doron Kushnir of the Weizmann Institute of Science who, along with Weizmann colleague Boaz Katz, put forward an new theory for Type Ia explosions that involves the violent collision of two white dwarfs.

Astronomers eagerly study the chemical signatures of the material ejected during these explosions in order to understand the mechanism and players involved in creating Type Ia supernovae. "One exciting possibility is that we are seeing material being stripped from the exploding white dwarf's companion star as the supernova collides with it," said Anthony Piro. "If this is the case, it would be the first-ever observation of such an occurrence."

"I have been looking for this signature for a decade!" said co-author Josh Simon. "We finally found it, but it's so rare, which is an important piece of the puzzle for solving the mystery of how Type Ia supernovae originate." In recent years, astronomers have discovered a small number of rare Type Ia supernovae that are cloaked in large amount of hydrogen—maybe as much as the mass of our Sun. But in several respects, ASASSN-18tb is different from these previous events.

But now astronomers at MIT and elsewhere have found that these first stars may have blown apart in a more powerful, asymmetric fashion, spewing forth jets that were violent enough to eject heavy elements into neighboring galaxies. These elements ultimately served as seeds for the second generation of stars, some of which can still be observed today.

In a paper published today in the Astrophysical Journal, the researchers report a strong abundance of zinc in HE 1327-2326, an ancient, surviving star that is among the universe's second generation of stars. They believe the star could only have acquired such a large amount of zinc after an asymmetric explosion of one of the very first stars had enriched its birth gas cloud.

Some episodes in the Milky Way's history, however, were so cataclysmic that they are difficult to hide. Scientists have known for some time that the Milky Way's halo of stars drastically changes in character with distance from the galactic center as revealed by the composition of the stars (their "metallicity"), the stellar motions, and the stellar density. CfA astronomer Federico Marinacci and his colleagues analyzed a suite of computer cosmological simulations and the galaxy interactions in them. In particular they analyzed the history of galaxy halos as they evolved following a merger event. They conclude that six to ten billion years ago the Milky Way merged in a head-on collision with a massive dwarf galaxy containing about one-to-ten billion solar masses in size, and that this collision could produce the character changes in stellar population currently observed in the Milky Way's stellar halo.

March

Massive clusters of galaxies, some with more mass than a hundred Milky Way galaxies, have been detected from cosmic epochs as early as about three billion years after the big bang. Their ongoing star formation makes them bright enough to be detected at these distances. These kinds of clusters were predicted by simulations of cosmological evolution but their properties are very uncertain.

Not only can there be bursts of activity, prompted perhaps by a collision with a neighboring galaxy, but the opposite can occur. Star formation can be self- limiting because its massive young stars produce winds and supernovae that can blow apart the natal molecular clouds and disable future star formation. Combined with the disruption induced by jets from an active nuclear supermassive black hole, this disruptive process is called quenching and is thought to be able to bring star formation to a halt. Whether or not this occurs in the early universe, and when and how it proceeds, is a key area of comic research.

April

J0023+0307 lithium

this star is similar to our sun, but with a much poorer metal content, less than one thousandth part of that of the solar metallicity. This composition implies that we are dealing with a star which was formed in the first 300 million years of the universe,

a red giant branch star with an effective temperature of about 4,850 K, and has a remarkably low abundances of heavier elements, including an extremely low abundance of iron at a level of -6.2.

Black holes

December

Because galaxy clusters are full of gas, early theories about them predicted that as the gas cooled, the clusters would see high rates of star formation, which need cool gas to form. However, these clusters are not as cool as predicted and, as such, weren't producing new stars at the expected rate. Something was preventing the gas from fully cooling. The culprits were supermassive black holes, whose outbursts of plasma keep the gas in galaxy clusters too warm for rapid star formation. The recorded outburst in SPT-0528 has another peculiarity that sets it apart from other black hole outbursts. It's unnecessarily large. Astronomers think of the process of gas cooling and hot gas release from black holes as an equilibrium that keeps the temperature in the galaxy cluster—which hovers around 18 million degrees Fahrenheit—stable. "It's like a thermostat," says McDonald. The outburst in SPT-0528, however, is not at equilibrium. According to Calzadilla, if you look at how much power is released as gas cools onto the black hole versus how much power is contained in the outburst, the outburst is vastly overdoing it. In McDonald's analogy, the outburst in SPT-0528 is a faulty thermostat. "It's as if you cooled the air by 2 degrees, and thermostat's response was to heat the room by 100 degrees," McDonald explains. Earlier in 2019, McDonald and colleagues released a paper looking at a different galaxy cluster, one that displays a completely opposite behavior to that of SPT-0528. Instead of an unnecessarily violent outburst, the black hole in this cluster, dubbed Phoenix, isn't able to keep the gas from cooling. Unlike all the other known galaxy clusters, Phoenix is full of young star nurseries, which sets it apart from the majority of galaxy clusters. "With these two galaxy clusters, we're really looking at the boundaries of what is possible at the two extremes," McDonald says of SPT-0528 and Phoenix. He and Calzadilla will also characterize the more normal galaxy clusters, in order to understand the evolution of galaxy clusters over cosmic time. To explore this, Calzadilla is characterizing 100 galaxy clusters. The reason for characterizing such a large collection of galaxy clusters is because each telescope image is capturing the clusters at a specific moment in time, whereas their behaviors are happening over cosmic time. These clusters cover a range of distances and ages, allowing Calzadilla to investigate how the properties of clusters change over cosmic time. "These are timescales that are much bigger than a human timescale or what we can observe," explains Calzadilla.

Super-Eddington accretion on to massive black hole seeds may be commonplace in the early Universe, where the conditions exist for rapid accretion. Direct-collapse black holes are often invoked as a possible solution to the observation of supermassive black holes (SMBHs) in the pre-reionization Universe. We investigate here how feedback, mainly in the form of bipolar jets, from super-Eddington accreting seed black holes will affect their subsequent growth. We find that, nearly independently of the mass loading of the bipolar jets, the violent outflows generated by the jets evacuate a region of approximately 0.1 pc surrounding the black hole seed. However, the jet outflows are unable to break free of the halo and their impact is limited to the immediate vicinity of the black hole. The outflows suppress any accretion for approximately a dynamical time. The gas then cools, recombines, and falls back to the centre, where high accretion rates are again observed. The overall effect is to create an effective accretion rate with values of between 0.1 and 0.5 times the Eddington rate. If this episodic accretion rate is maintained for order 500 million years, then the black hole will increase in mass by a factor of between 3 and 300 but far short of the factor of 104 required for the seeds to become the SMBHs observed at z > 6. Therefore, direct-collapse black holes born into atomic cooling haloes and which experience strong negative mechanical feedback will require external influences (e.g. rapid major mergers with other haloes) to promote efficient accretion and reach SMBH masses within a few hundred million years.

November

"Our calculations show that tens of thousands of planets with 10 times the mass of the Earth could be formed around 10 light-years from a black hole," says Eiichiro Kokubo, a professor at the National Astronomical Observatory of Japan who studies planet formation. "Around black holes, there might exist planetary systems of astonishing scale." Some supermassive black holes have large amounts of matter around them in the form of a heavy, dense disk. A disk can contain as much dust as 100,000 times the mass of the sun. This is 1 billion times the dust mass of a protoplanetary disk. In a low temperature region of a protoplanetary disk, dust grains with ice mantles stick together and evolve into fluffy aggregates. A dust disk around a black hole is so dense that the intense radiation from the central region is blocked and low temperature regions are formed. The researchers applied the planet formation theory to circumnuclear disks and found that planets could form over several hundred million years.

It seems that black holes can run hot or cold when it comes to either enhancing or squelching star birth inside a cluster of galaxies. Typically, giant black holes, pumping out energy via jets, keep interstellar gas too warm to condense and form stars. Now, astronomers have found a cluster of galaxies, called the Phoenix cluster, where stars are forming at a furious rate because of the black hole's influence. This stellar turboboost is apparently linked to less energetic jets from a central black hole that do not pump up the gas temperature. Instead, the gas loses energy as it glows in X-rays. The gas cools to where it can form large numbers of stars at a breathtaking rate. Where our Milky Way forms one star per year on average, newborn stars are popping out of this cool gas at a rate of about 500 solar masses per year in the Phoenix cluster. Unraveling this mystery required the combined power of NASA's Hubble Space Telescope, NASA's Chandra X-ray Observatory, and the Very Large Array (VLA) radio observatory near Socorro, New Mexico. The VLA radio data reveals jets blasting out from the vicinity of the central black hole. These jets inflated bubbles in the hot gas that are detected in X-rays by Chandra. Hubble resolves bright blue filaments of newborn stars in cavities between the hot jet and gas clouds. As the black hole has grown more massive and more powerful, its influence has been increasing.Sironi said that the crucial point of the study was to identify role magnetic reconnection plays within the turbulent environment. The simulations showed that reconnection is the key mechanism that selects the particles that will be subsequently accelerated by the turbulent magnetic fields up to the highest energies The simulations also revealed that particles gained most of their energy by bouncing randomly at an extremely high speed off the turbulence fluctuations. When the magnetic field is strong, this acceleration mechanism is very rapid. But the strong fields also force the particles to travel in a curved path, and by doing so, they emit electromagnetic radiation.

In a study published in the December issue of The Astrophysical Journal, astrophysicists Luca Comisso and Lorenzo Sironi employed massive super-computer simulations to calculate the mechanisms that accelerate these particles. They concluded that their energization is a result of the interaction between chaotic motion and reconnection of super-strong magnetic fields. "Turbulence and magnetic reconnection—a process in which magnetic field lines tear and rapidly reconnect—conspire together to accelerate particles, boosting them to velocities that approach the speed of light," said Luca Comisso, a postdoctoral research scientist at Columbia and first author on the study "The region that hosts black holes and neutron stars is permeated by an extremely hot gas of charged particles, and the magnetic field lines dragged by the chaotic motions of the gas, drive vigorous magnetic reconnection," he added. "It is thanks to the electric field induced by reconnection and turbulence that particles are accelerated to the most extreme energies, much higher than in the most powerful accelerators on Earth, like the Large Hadron Collider at CERN. When studying turbulent gas, scientists cannot predict chaotic motion precisely. Dealing with the mathematics of turbulence is difficult, and it constitutes one of the seven "Millennium Prize" mathematical problems. To tackle this challenge from an astrophysical point of view, Comisso and Sironi designed extensive super-computer simulations —among the world's largest ever done in this research area—to solve the equations that describe the turbulence in a gas of charged particles.

An international team headed by Professor LIU Jifeng of the National Astronomical Observatory of China of the Chinese Academy of Sciences (NAOC) spotted a stellar black hole with a mass 70 times greater than the sun. The monster black hole is located 15,000 light-years from Earth and has been named LB-1 by the researchers. The Milky Way galaxy is estimated to contain 100 million stellar black holes—cosmic bodies formed by the collapse of massive stars and so dense even light can't escape. Until now, scientists had estimated the mass of an individual stellar black hole in our galaxy at no more than 20 times that of the sun. But the discovery of a huge black hole by a Chinese-led team of international scientists has toppled that assumption. The team, headed by Prof. LIU Jifeng of the National Astronomical Observatory of China of the Chinese Academy of Sciences (NAOC), spotted a stellar black hole with a mass 70 times greater than the sun. The monster black hole is located 15 thousand light-years from Earth and has been named LB-1 by the researchers. The discovery is reported in the latest issue of Nature. The discovery came as a big surprise. "Black holes of such mass should not even exist in our galaxy, according to most of the current models of stellar evolution," said Prof. LIU. "We thought that very massive stars with the chemical composition typical of our galaxy must shed most of their gas in powerful stellar winds, as they approach the end of their life. Therefore, they should not leave behind such a massive remnant. LB-1 is twice as massive as what we thought possible. Now theorists will have to take up the challenge of explaining its formation."

October

At the center of a galaxy called NGC 1068, a supermassive black hole hides within a thick doughnut-shaped cloud of dust and gas. When astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) to study this cloud in more detail, they made an unexpected discovery that could explain why supermassive black holes grew so rapidly in the early Universe. "Surprisingly, we found two disks of gas rotating in opposite directions." "Counter-rotating gas streams are unstable, which means that clouds fall into the black hole faster than they do in a disk with a single rotation direction," said Impellizzeri. "This could be a way in which a black hole can grow rapidly." NGC 1068 (also known as Messier 77) is a spiral galaxy approximately 47 million light-years from Earth in the direction of the constellation Cetus. At its center is an active galactic nucleus, a supermassive black hole that is actively feeding itself from a thin, rotating disk of gas and dust, also known as an accretion disk.

Astronomers at the University of California, Riverside, have discovered that powerful winds driven by supermassive black holes in the centers of dwarf galaxies have a significant impact on the evolution of these galaxies by suppressing star formation. Astronomers suspect that when wind emanating from a black hole is pushed out, it compresses the gas ahead of the wind, which can increase star formation. But if all the wind gets expelled from the galaxy's center, gas becomes unavailable and star formation could decrease. The latter appears to be what is occurring in the six dwarf galaxies the researchers identified. "In these six cases, the wind has a negative impact on star formation," Sales said. "Theoretical models for the formation and evolution of galaxies have not included the impact of black holes in dwarf galaxies. We are seeing evidence, however, of a suppression of star formation in these galaxies. Our findings show that galaxy formation models must include black holes as important, if not dominant, regulators of star formation in dwarf galaxies."

The supermassive black hole at the heart of our galaxy spat out an enormous flare of radiation 3.5 million years ago that would have been clearly visible from Earth.In new research that will soon be published in the Astrophysical Journal my colleagues and I found that the flare left traces in a trail of gas called the Magellanic Stream that lies some 200,000 light years away and encircles the Milky Way. This activity has been flickering on and off for billions of years. We don't understand why this activity is intermittent, but it has something to do with how material gets dumped onto the black hole. It might be like water droplets on a hot plate that sputter and explode chaotically, depending on their size.

A titanic, expanding beam of energy sprang from close to the supermassive black hole in the centre of the Milky Way just 3.5 million years ago, sending a cone-shaped burst of radiation through both poles of the Galaxy and out into deep space. That's the finding arising from research conducted by a team of scientists led by Professor Joss Bland-Hawthorn from Australia's ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3-D) and soon to be published in The Astrophysical Journal. The phenomenon, known as a Seyfert flare, created two enormous 'ionisation cones' that sliced through the Milky Way—beginning with a relatively small diameter close to the black hole, and expanding vastly as they exited the Galaxy.

Thompson began combing through the data, looking for stars that showed that change, indicating that they might be orbiting a black hole. Then, he narrowed the APOGEE data to 200 stars that might be most interesting. He gave the data to a graduate research associate at Ohio State, Tharindu Jayasinghe, who compiled thousands of images of each potential binary system from ASAS-SN, the All-Sky Automated Survey for Supernovae. (ASAS-SN has found some 1,000 supernovae, and is run out of Ohio State.) Their data crunching found a giant red star that appeared to be orbiting something, but that something, based on their calculations, was likely much smaller than the known black holes in the Milky Way, but way bigger than most known neutron stars. After more calculations and additional data from the Tillinghast Reflector Echelle Spectrograph and the Gaia satellite, they realized they had found a low-mass black hole, likely about 3.3 times the mass of the sun.

September

"There has been a lot of uncertainty regarding the SMBH-galaxy connection, in particular whether SMBH growth was more tightly connected to the star formation rate or the mass of the host galaxy," said Yale astrophysicist Priyamvada Natarajan, senior investigator of the new study, which appears in the journal Monthly Notices of the Royal Astronomical Society. "These results represent the most thorough theoretical evidence for the former—the growth rate of black holes appears to be tightly coupled to the rate at which stars form in the host." Called Romulus, the cosmological simulation follows the evolution of different regions of the universe from just after the Big Bang until the present day and includes thousands of simulated galaxies that reside in a wide variety of cosmic environments. "If the SMBH starts to grow too rapidly and gets too big for its galactic home, physical processes ensure that its growth slows down relative to the galaxy," Tremmel explained. "On the other hand, if the SMBH's mass is too small for its galaxy, the SMBH's growth rate increases relative to the size of the galaxy to compensate." June

Although our galactic center black hole is relatively quiet, the radiation around it is strong enough to cause hydrogen atoms to continually lose and recombine with their electrons. This recombination produces a distinctive millimeter-wavelength signal, which is capable of reaching Earth with very little losses along the way.

With its remarkable sensitivity and powerful ability to see fine details, the Atacama Large Millimeter/submillimeter Array (ALMA) was able to detect this faint radio signal and produce the first-ever image of the cooler gas disk at only about a hundredth of a light-year away (or about 1000 times the distance from the Earth to the Sun) from the supermassive black hole. These observations enabled the astronomers both to map the location and trace the motion of this gas. The researchers estimate that the amount of hydrogen in this cool disk is about one tenth the mass of Jupiter, or one ten-thousandth of the mass of the Sun.

An international team has constructed the most detailed, highest resolution simulation of a black hole to date. The simulation proves theoretical predictions about the nature of accretion disks—the matter that orbits and eventually falls into a black hole—that have never before been seen. he inner-most region of an accretion disk aligns with its black hole's equator. This discovery solves a longstanding mystery, originally presented by Nobel Prize-winning physicist John Bardeen and astrophysicist Jacobus Petterson in 1975. At the time, Bardeen and Petterson argued that a spinning black hole would cause the inner region of a tilted accretion disk to align with its black hole's equatorial plane. After a decades-long, global race to find the so-called Bardeen-Petterson effect, the team's simulation found that, whereas the outer region of an accretion disk remains tilted, the disk's inner region aligns with the black hole.

ALMA observations reveal a never-before-seen disk of cool, interstellar gas wrapped around the supermassive black hole at the center of the Milky Way. We now know that this region is brimming with roving stars, interstellar dust clouds, and a large reservoir of both phenomenally hot and comparatively colder gases. These gases are expected to orbit the black hole in a vast accretion disk that extends a few tenths of a light-year from the black hole's event horizon.

The neutron star, called J0740+6620, is a rapidly spinning pulsar that packs 2.17 times the mass of the sun (which is 333,000 times the mass of the Earth) into a sphere only 20-30 kilometers, or about 15 miles, across. This measurement approaches the limits of how massive and compact a single object can become without crushing itself down into a black hole.

An international team of astronomers, including Northwestern University's Farhad Yusef-Zadeh, has discovered one of the largest structures ever observed in the Milky Way. A newly spotted pair of radio-emitting bubbles reach hundreds of light-years tall, dwarfing all other structures in the central region of the galaxy. The team believes the enormous, hourglass-shaped structure likely is the result of a phenomenally energetic burst that erupted near the Milky Way's supermassive black hole several million years ago. "The center of our galaxy is relatively calm when compared to other galaxies with very active central black holes," said Ian Heywood of the University of Oxford, first author of study. "Even so, the Milky Way's central black hole can—from time to time—become uncharacteristically active, flaring up as it periodically devours massive clumps of dust and gas. It's possible that one such feeding frenzy triggered powerful outbursts that inflated this previously unseen feature." For this work, the team used the South African Radio Astronomy Observatory (SARAO) MeerKAT telescope, the largest science project in Africa. "These enormous bubbles have until now been hidden by the glare of extremely bright radio emission from the center of the galaxy,"

July

Data from ESA's XMM-Newton X-ray observatory has revealed how supermassive black holes shape their host galaxies with powerful winds that sweep away interstellar matter. In a new study, scientists analysed eight years of XMM-Newton observations of the black hole at the core of an active galaxy known as PG 1114+445, showing how ultrafast winds—outflows of gas emitted from the accretion disk very close to the black hole—interact with the interstellar matter in central parts of the galaxy. These outflows have been spotted before but the new study clearly identifies, for the first time, three phases of their interaction with the host galaxy. "These winds might explain some surprising correlations that scientists have known about for years but couldn't explain," said lead author Roberto Serafinelli of the National Institute of Astrophysics in Milan, Italy, who conducted most of the work as part of his Ph.D. at University of Rome Tor Vergata. "For example, we see a correlation between the masses of supermassive black holes and the velocity dispersion of stars in the inner parts of their host galaxies. But there is no way this could be due to the gravitational effect of the black hole. Our study for the first time shows how these black hole winds impact the galaxy on a larger scale, possibly providing the missing link." Astronomers have previously detected two types of outflows in the X-ray spectra emitted by the active galactic nuclei, the dense central regions of galaxies known to contain supermassive black holes. The so-called ultra-fast outflows (UFOs), made of highly ionised gas, travel at speeds up to 40 percent the speed of light and are observable in the vicinity of the central black hole. April

An international team of researchers, led by Kavli Institute for the Physics and Mathematics of the Universe Principal Investigator Masahiro Takada, PhD candidate student Hiroko Niikura, Professor Naoki Yasuda, and including researchers from Japan, India and the US, have used the gravitational lensing effect to look for primordial black holes between Earth and the Andromeda galaxy. So to maximize the chances of capturing an event, the researchers used the Hyper Suprime-Cam on the Subaru Telescope, which can capture the whole image of the Andromeda galaxy in one shot. From 190 consecutive images of the Andromeda galaxy taken over seven hours during one clear night, the team scoured the data for potential gravitational lensing events. If dark matter consists of primordial black holes of a given mass, in this case masses lighter than the moon, the researchers expected to find about 1000 events. But after careful analyses, they could only identify one case. The team's results showed primordial black holes can contribute no more than 0.1 per cent of all dark matter mass. Therefore, it is unlikely the theory is true

June

The strong magnetic field at the center of the Milky Way galaxy. Scientists used SOFIA's newest instrument, the High-resolution Airborne Wideband Camera-Plus, HAWC+, to make these measurements.The new observations with HAWC+ reveal that the magnetic field is strong enough to constrain the turbulent motions of gas. If the magnetic field channels the gas so it flows into the black hole itself, the black hole is active, because it is eating a lot of gas. However, if the magnetic field channels the gas so it flows into an orbit around the black hole, then the black hole is quiet because it's not ingesting any gas that would otherwise eventually form new stars. These jets essentially choke off the gas supply of the galaxy, so no more gas can fall on to the galaxy and form new stars. After a galaxy has stopped forming stars, we say it's a passive dead galaxy." But in Kirkpatrick's survey, about 10 percent of galaxies hosting accreting supermassive black holes had a supply of cold gas remaining after entering this phase, and still made new stars. Previous observations from SOFIA show the tilted ring of gas and dust orbiting the Milky Way's black hole, which is called Sagittarius A* (pronounced "Sagittarius A-star"). But the new HAWC+ data provide a unique view of the magnetic field in this area, which appears to trace the region's history over the past 100,000 years. Details of these SOFIA magnetic field observations were presented at the June 2019 meeting of the American Astronomical Society and will be submitted to the Astrophysical Journal.In order to measure the pressure in the heliosheath, the scientists used the Voyager spacecraft, which have been travelling steadily out of the solar system since 1977. At the time of the observations, Voyager 1 was already outside of the heliosphere in interstellar space, while Voyager 2 still remained in the heliosheath. "There was really unique timing for this event because we saw it right after Voyager 1 crossed into the local interstellar space," Rankin said. "And while this is the first event that Voyager saw, there are more in the data that we can continue to look at to see how things in the heliosheath and interstellar space are changing over time." When one such wave reached the heliosheath in 2012, it was spotted by Voyager 2. The wave caused the number of galactic cosmic rays to temporarily decrease. Four months later, the scientists saw a similar decrease in observations from Voyager 1, just across the solar system's boundary in interstellar space. Knowing the distance between the spacecraft allowed them to calculate the pressure in the heliosheath as well as the speed of sound. In the heliosheath sound travels at around 300 kilometers per second—a thousand times faster than it moves through air. The scientists noted that the change in galactic cosmic rays wasn't exactly identical at both spacecraft. At Voyager 2 inside the heliosheath, the number of cosmic rays decreased in all directions around the spacecraft. But at Voyager 1, outside the solar system, only the galactic cosmic rays that were traveling perpendicular to the magnetic field in the region decreased. This asymmetry suggests that something happens as the wave transmits across the solar system's boundary. "In adding up the pieces known from previous studies, we found our new value is still larger than what's been measured so far," said Jamie Rankin, lead author on the new study and astronomer at Princeton University in New Jersey. "It says that there are some other parts to the pressure that aren't being considered right now that could contribute."

Dark Matter

March

After drawing both praise and skepticism, the team of astronomers who discovered NGC 1052-DF2 – the very first known galaxy to contain little to no dark matter – are back with stronger evidence about its bizarre nature.you always have a little voice in the back of your mind saying, 'but what if you're wrong?' Globular clusters are behaving exactly as they should

Like DF2, DF4 belongs to a relatively new class of galaxies called ultra-diffuse galaxies (UDGs). They are as large as the Milky Way but have between 100 to 1000 times fewer stars,

Ironically, the lack of dark matter in these UDGs strengthens the dark matter theory. It proves that dark matter is a substance that is not coupled to 'normal' matter, as both can be found separately. The discovery of these galaxies is difficult to explain in theories that change the laws of gravity on large scales as an alternative to the dark matter hypothesis.

Mars

December

The landslide shows long ridges that extend in the direction of the movement for almost the entire length of the deposit. As mentioned, these ridges have previously been interpreted to be a result of underlying ice at the time of the landslide. This hypothesis is supported by the fact that similar structures have been observed on terrestrial landslides on glaciers. Based on this similarity, the presence of the ridges on martian landslides have been used in support of the theory that Mars was once covered in ice. But the presence of glaciers and their timing at such martian latitude is hotly debated. What's more, it is still unclear which exact mechanisms created these ridges during the ice age. To investigate whether there may be other explanations, we made computer models of the landslide called "digital elevation" models. These are 3-D representations of terrain, obtained from high-resolution satellite images and the terrain's elevation data. From this data, we could calculate the thickness of the landslides, the length of the ridges, their height and their wavelength—that is the distance from crest to crest between two ridges next to each other. This suggests that ice is not a necessary condition for the formation of the long ridges. Instead, we propose that the ridges could have formed at high speeds due to underlying layers of unstable, light rocks. These layers would have been created by vibrations and collisions of rock particles at the bottom of the slide with the rough surface of the valley. This would have initiated a "convection process"—transfer of heat by movement—that caused upper denser and heavier layers of rock to fall and lighter rocks to rise.

October

The findings, published today in Nature Communications, show for the first time that the unique structures on Martian landslides from mountains several kilometres high could have formed at high speeds of up to 360 kilometres per hour due to underlying layers of unstable, fragmented rocks This challenges the idea that underlying layers of slippery ice can only explain such long vast ridges, which are found on landslides throughout the Solar System. First author, Ph.D. student Giulia Magnarini (UCL Earth Sciences), said: "Landslides on Earth, particularly those on top of glaciers, have been studied by scientists as a proxy for those on Mars because they show similarly shaped ridges and furrows, inferring that Martian landslides also depended on an icy substrate. "However, we've shown that ice is not a prerequisite for such geological structures on Mars, which can form on rough, rocky surfaces. This helps us better understand the shaping of Martian landscapes and has implications for how landslides form on other planetary bodies including Earth and the Moon."

August

Three years ago, a team of researchers found evidence on Mars that suggested a giant tsunami had occurred billions of years ago—not long after the formation of the planet. The evidence consisted of geological formations that resembled some on Earth that had been formed by a tsunami. That led the researchers with this new effort to try to trace back the possible origin of such a tsunami. Suspecting that it was likely due to a celestial body of some sort impacting the planet, the team began looking for craters in the area that might fit with their prior observations. After studying several candidates, the researchers settled on Lomonosov because it appeared to be both from the same time period as the possible tsunami and the right size. It was also in the right place and bore a striking resemblance to marine craters on Earth. A closer look at the crater showed that part of its rim was missing, possible evidence that it was worn down by backwash as displaced water returned. The researchers also noted that the crater appeared to be approximately the same theoretical depth as the ancient Mars ocean.

For centuries, miners have burrowed into the earth in search of salt—laid down in thick layers from ancient oceans long since evaporated. When scientists saw huge deposits of salt on Mars, they immediately wondered whether it meant Mars too once had giant oceans. Yet it's remained unclear what those deposits meant about the Red Planet's climate. A new study by UChicago researchers shakes up the picture of Martian salt—and offers new ways to test what Mars' water would have looked like. "They're not in the right places to mark the deaths of oceans, but they date from when Mars' climate transitioned from the early era of rivers and overspilling lakes to the cold, desert planet we see today," said study author Edwin Kite, assistant professor of geophysical sciences at the University of Chicago and an expert in both the history of Mars and climates of other worlds. "So these salt deposits might tell us something about how and why Mars dried out." The salt in Martian deposits isn't the same as the salt of Earth's oceans—it's actually more similar to Epsom salts, made out of two ingredients: magnesium and sulfuric acid. Figuring out how those two chemicals combined can give us information about what Mars' climate used to look like. One possibility is that Mars had water that circulated deep underground, carrying magnesium to the surface where it reacted with sulfuric acid. That means the planet would have been warm enough to allow groundwater to flow. The problem is, while too much carbon dioxide in the atmosphere warms the planet—as we're finding out on Earth—too little will freeze it. If too much carbon was locked into the ground and the resulting atmosphere was too thin to keep Mars warm, the groundwater movement would halt as the planet froze. And the analysis found the cycle would lock up a lot of carbon. This doesn't sound promising for the groundwater scenario, Kite said, but it doesn't disprove it. "Most of our model runs disfavored groundwater, but we also found a few 'loopholes' that could allow Mars to keep enough carbon in the atmosphere," he said. The methane puffing from a huge crater on Mars could be a sign of life or other non-biological activity under the planet's surface. Gale crater, which is 154 km in diameter and about 3.8 billion years old, is thought by some to contain an ancient lakebed. The team was able to improve the estimate of methane by using data from a satellite, ExoMars Trace Gas Orbiter, and the Curiosity Rover, which collects rock, soil and air samples for onboard analysis. "We were able—for the first time—to calculate a single number for the rate of seepage of methane at Gale crater on Mars that is equivalent to an average of 2.8 kg per Martian day." Dr. Moores said the team was able to reconcile the data from the ExoMars Trace Gas Orbiter and the Curiosity Rover, which appeared to contradict each other with wildly different detections of methane. "We were able to resolve these differences by showing how concentrations of methane were much lower in the atmosphere during the day and significantly higher near the planet's surface at night, as heat transfer lessens," he said. June

"meteoric smoke"—essentially, the icy dust created by space debris slamming into the planet's atmosphere. "We're used to thinking of Earth, Mars and other bodies as these really self-contained planets that determine their own climates," said Victoria Hartwick, a graduate student in the Department of Atmospheric and Ocean Sciences (ATOC) and lead author of the new study. "But climate isn't independent of the surrounding solar system." "Clouds don't just form on their own," said Hartwick, also of the Laboratory for Atmospheric and Space Physics at CU Boulder. "They need something that they can condense onto." as far as scientists can tell, those sorts of cloud seeds don't exist in Mars' middle atmosphere, Hartwick said. And that's what led her and her colleagues to meteors. Hartwick explained that about two to three tons of space debris crash into Mars every day on average. And as those meteors rip apart in the planet's atmosphere, they inject a huge volume of dust into the air. To find out if such smoke would be enough to give rise to Mars' mysterious clouds, Hartwick's team turned to massive computer simulations that attempt to mimic the flows and turbulence of the planet's atmosphere. And sure enough, when they included meteors in their calculations, clouds appeared. "Our model couldn't form clouds at these altitudes before," Hartwick said. "But now, they're all there, and they seem to be in all the right places."

Western researchers, leading an international team, have shown that the first 'real chance' of Mars developing life started early, 4.48 billion years ago, when giant, life-inhibiting meteorites stopped striking the Red Planet. The findings not only clarify possibilities for Earth's nearest neighbour, but may reset the timeline for life on our home planet, as well.

Western researchers suggest that conditions under which life could have thrived may have occurred on Mars from around 3.5-4.2 billion years ago. This predates the earliest evidence of life on Earth by up to 500 million years. "Giant meteorite impacts on Mars may have actually accelerated the release of early waters from the interior of the planet setting the stage for life-forming reactions," Western researcher Desmond Moser said. "This work may point out good places to get samples returned from Mars." For the study, Moser and his team analyzed the oldest-known mineral grains from meteorites believed to have originated from Mars' southern highlands. These ancient grains, imaged down to atomic levels, are almost unchanged since they crystallized near the surface of Mars.

May

May

Approximately every two Earth years, when it is summer on the southern hemisphere of Mars, a window opens: Only in this season can water vapor efficiently rise from the lower into the upper Martian atmosphere. There, winds carry the rare gas to the north pole. While part of the water vapor decays and escapes into space, the rest sinks back down near the poles. Researchers from the Moscow Institute of Physics and Technology and the Max Planck Institute for Solar System Research (MPS) in Germany describe this unusual Martian water cycle in a current issue of the Geophysical Research Letters. Their computer simulations show how water vapor overcomes the barrier of cold air in the middle atmosphere of Mars and reaches higher atmospheric layers. This could explain why Mars, unlike Earth, has lost most of its water. The hydrogen escaped from there irretrievably into space. Measurements by space probes and space telescopes show that even today, water is still lost in this way. But how is this possible? The middle atmosphere layer of Mars, like Earth's tropopause, should actually stop the rising gas. After all, this region is usually so cold that water vapor would turn to ice. How does the Martian water vapor reach the upper air layers?

"When it is summer in the southern hemisphere, at certain times of day, water vapor can rise locally with warmer air masses and reach the upper atmosphere," says Paul Hartogh from MPS, summarizing the results of the new study. In the upper atmospheric layers, air flows carry the gas along the longitudes to the north pole, where it cools and sinks down again. However, part of the water vapor escapes this cycle: under the influence of solar radiation, the water molecules disintegrate and hydrogen escapes into space.

"The amounts of dust swirling through the atmosphere during such a storm facilitate the transport of water vapor into high air layers," says Alexander Medvedev from MPS.

The first study of ultra-small bacteria living in the extreme environment of Ethiopia's Dallol hot springs shows that life can thrive in conditions similar to those thought to have been found on the young planet Mars. An international team of researchers lead by Dr. Felipe Gómez from Astrobiology Center in Spain (CAB (CSIC-INTA)) has found a strain of the Nanohaloarchaeles Order bacteria embedded in samples taken from a salt chimney deposited by supersaturated water at temperatures of 89 degrees Celsius and at the extremely acidic pH of 0.25.

The microorganisms are 50-500 nanometers in diameter—up to 20 times smaller than the average bacteria. In several cases, the microorganisms are surrounded by needle-shaped crystals, which suggests that the nanobacteria may play an active role in the salt deposits and the geochemical cycle at Dallol. The Dallol volcano and geothermal area is one of the hottest places on Earth, with average annual temperatures of 36 to 38 degrees Celsius. It is located at the northern end of the Danakil Depression, which lies around 125m below sea level at the junction of three of the Earth's lithospheric plates (Arabian, Nubian and Somalian) that are moving apart.

Environments found on Mars, including the Gusev Crater, where NASA's Spirit Mars Exploration Rover landed. Last month, the same international team published a review in the journal Astrobiology, highlighting the importance of Dallol as a field analogue for Mars and for astrobiological studies.

Newly discovered layers of ice buried a mile beneath Mars' north pole are the remnants of ancient polar ice sheets and could be one of the largest water reservoirs on the planet, according to scientists at The University of Texas at Austin and the University of Arizona.The team made the discovery using measurements gathered by the Shallow Radar (SHARAD) on NASA's Mars Reconnaissance Orbiter (MRO). SHARAD emits radar waves that can penetrate up to a mile and a half beneath the surface of Mars. "That likely makes it the third largest water reservoir on Mars after the polar ice caps." March

University of Chicago; the runoff was intense—rivers on Mars were wider than those on Earth today—and occurred at hundreds of locations on the red planet. analyzed photographs and elevation models for more than 200 ancient Martian riverbeds spanning over a billion years. These riverbeds are a rich source of clues about the water running through them and the climate that produced it. For example, the width and steepness of the riverbeds and the size of the gravel tell scientists about the force of the water flow, and the quantity of the gravel constrains the volume of water coming through.

The authors think that the layers formed when ice accumulated at the poles during past ice ages on Mars. Each time the planet warmed, a remnant of the ice caps became covered by sand, which protected the ice from solar radiation and prevented it from dissipating into the atmosphere.

Jan

Despite the progress that has been made in studying these features, the scientific community remains divided into two camps when it comes to what causes Martian slope streaks. Those who belong to the "wet" mechanism school of thought believe that liquid water could be responsible for their creation, possibly as a result of groundwater springs, melting surface ice, or the formation of brines (salt solutions).

In contrast, those who fall into the "dry" mechanism school theorize that dust avalanches are responsible. These, in turn, could be caused by air fall deposits, subsurface melting, or localized disturbances – ranging by rockfalls, meteorite impacts, or tectonic activity ("marsquakes"). Both of these explanations have limitations when it comes to explaining observed slope streaks.

If liquid water or brines were the mechanism, then such slopes should only appear in areas that are experiencing warmer seasonal temperatures, which has not always been the case. slope streaks have been found to climb over obstacles in many instances, which is not consistent with liquid-driven displacement. After conducting drone-based observations of the region, the team determined that these streaks are a sufficient analog for a wet mechanism on Mars.

Pluto

At the time Pluto started moving away from the sun, astronomers expected that this would cause its atmospheric pressure to drop, in much the same way that the pressure in an automobile tyre decreases with cold weather and increases in the heat. On the contrary, observations from 1988-2016 have shown a steady increase in the atmospheric pressure.

Immediately before the arrival of NASA's New Horizons probe in 2015, occultation measurements discovered the atmospheric pressure on Pluto has tripled since 1988 (the equivalent on Earth would be to compare the pressure at the top of Mt Everest to that at sea level).

Even though Pluto is moving farther from the Sun every year, its north pole is continuously sunlit during this part of its orbit, causing its nitrogen ice cap to revert to the gas phase.

This explains the rapid increase of atmospheric pressure over the past three decades. But the climate modelling shows this trend will not continue. Pluto will continue to move farther from the Sun until the year 2113, and the weak sunlight will not be sufficient to similarly warm the southern polar regions.

During the long northern autumn and winter, Pluto's atmosphere is expected to collapse, frosting out onto the surface like ice on a car windscreen on a clear and cold winter night.

a part of Pluto's surface known as Virgil Fossa—an area around a large crack in the surface. Prior research has suggested the crack was the result of volcanic activity. The researchers chose to focus on the site because its reddish-brown color hinted at the possible presence of ammonia on the surface—a rarity in planetary research. Ammonia does not last long on the surface of planetary bodies because it is easily broken down by cosmic rays and ultraviolet light. Data from New Horizons provided a near-infrared spectrum of the surface at a resolution of 2,700 meters per pixel, showing some water ice on the surface and some ammonia.

a part of Pluto's surface known as Virgil Fossa—an area around a large crack in the surface. Prior research has suggested the crack was the result of volcanic activity. The researchers chose to focus on the site because its reddish-brown color hinted at the possible presence of ammonia on the surface—a rarity in planetary research. Ammonia does not last long on the surface of planetary bodies because it is easily broken down by cosmic rays and ultraviolet light. Data from New Horizons provided a near-infrared spectrum of the surface at a resolution of 2,700 meters per pixel, showing some water ice on the surface and some ammonia.

But the exact opposite occurs. The proof is provided by the article that appeared in A&A of May 10, 2019, and which analyses a dozen of stellar occultations observed in nearly 30 years, during the spring in the northern hemisphere of Pluto: the atmospheric pressure increases by a factor of three between 1988 and 2016.

New Horizons mapped the distribution and topography of ice on the surface of the dwarf planet, revealing a vast depression of more than 1000 km in diameter and 4 km deep, located near the equator between latitudes 25 ° S and 50 ° N, and called Sputnik Planitia. This depression locks up a part of the nitrogen available in the atmosphere, forming a gigantic glacier which is the true "heart" of the climate of the dwarf planet, since it regulates the atmospheric circulation via the sublimation of the nitrogen.

In addition, stellar occultations allow to constrain the subsoil's thermal inertia of the model, explaining the thirty-year phase shift between the transition to perihelion (1989) and the growth in pressure still observed today (Fig. 1). The subsoil has stored the heat and is restoring it gradually. Occultations also constrain the fraction of solar energy returned to space (bond albedo) of nitrogen ice and its emissivity.

Finally, these observations eliminate the possibility for the presence of a reservoir of nitrogen in the southern hemisphere (currently in a permanent night), which would produce a maximum of pressure much earlier than what is observed

Jupiter

The shrinking of the clouds of the Great Red Spot on Jupiter has been well documented with photographic evidence from the last decade. However, researchers said there is no evidence the vortex itself has changed in size or intensity. Philip Marcus, from the University of California, Berkeley, will explain why the pictures from astronomers, both professionals and amateur, are not telling the whole story about the Great Red Spot. His session, The Shedding of Jupiter's Red Flakes Does Not Mean It Is Dying, will take place at the American Physical Society's Division of Fluid Dynamics 72nd Annual Meeting on Nov. 25 at the Washington State Convention Center in Seattle. Marcus said the visible clouds hide the true size and nature of the vortex of the Great Red Spot. In the spring of 2019, observers photographed large red "flakes" being ripped from the familiar red spot, but Marcus said the flaking phenomena is a very natural state of a vortex with cloud coverage and not an indication of the Great Red Spot's death. "I don't think its fortunes were ever bad," Marcus said. "It's more like Mark Twain's comment: The reports about its death have been greatly exaggerated." Marcus discuss how smaller cloud formation bumped into the Great Red Spot, sometimes creating stagnation points, where the velocity abruptly stops, restarts and goes off in different directions. These points indicate where an approaching cloud shattered and created the flakes that were observed by astronomers. "The loss of undigested clouds from the GRS through encounters with stagnation points does not signify the demise of the GRS," he said. "The proximity of the stagnation points to the GRS during May and June does not signify its demise. The creation of little vortices to the east, northeast of the GRS during the spring of 2019 and their subsequent merging with the GRS with some does not signify its demise." Marcus said a secondary circulation, driven by the heating and cooling above and below the vortex, allows the Great Red Spot to continue to exist over th