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HD 10180 is a Sun-like star in the southern constellation Hydrus that is notable for its large planetary system. Since its discovery, at least seven planets, and possibly as many as nine, have been observed orbiting it, making it potentially the largest of all known planetary systems, including the Solar System.[8][5](Other stars with a large known number of planets include Kepler-90, TRAPPIST-1, Kepler-11, and 55 Cancri.)

HD 10180
View of the sky around the star HD 10180 (center)
Credit: ESO
Observation data
Epoch J2000      Equinox J2000
Constellation Hydrus
Right ascension  01h 37m 53.57672s[1]
Declination −60° 30′ 41.4954″[1]
Apparent magnitude (V) 7.33[2]
Spectral type G1V[3]
Radial velocity (Rv)+35.2[3] km/s
Proper motion (μ) RA: -14.60[1] mas/yr
Dec.: 6.51[1] mas/yr
Parallax (π)25.63 ± 0.38[1] mas
Distance127 ± 2 ly
(39.0 ± 0.6 pc)
Mass1.062 ± 0.017[4] M
Radius1.20 ± 0.318[4] R
Luminosity1.49 ± 0.02[5] L
Surface gravity (log g)4.39[6] cgs
Temperature5,911[6] K
Metallicity [Fe/H]0.08[6] dex
Rotation24 ± 3 days[5]
Rotational velocity (v sin i)< 3[5] km/s
Age7.3[7] Gyr
Other designations
CD–61°285, HD 10180, HIP 7599, SAO 248411.[2]
Database references


Based upon parallax measurements, it is located at a distance of about 127 light-years (39 parsecs) from Earth.[9] The apparent visual magnitude of this star is 7.33, which is too faint to be viewed with the naked eye although it can be readily observed with a small telescope.[10] At a declination of −60°, this star cannot be seen at latitudes north of the tropics.

HD 10180 is a G1V-type star, and thus generates energy at its core through the thermonuclear fusion of hydrogen. The mass of this star is estimated as 6% greater than the Sun's mass, it has a radius of 120% that of the Sun, and is radiating 149% of the Sun's luminosity. The effective temperature of the star's chromosphere is 5,911 K, giving it a yellow-hued glow like the Sun.[11] HD 10180 has a 20% higher abundance of elements other than hydrogen/helium compared to the Sun.[note 1] With an estimated age of 7.3 billion years, it is a stable star with no significant magnetic activity. The estimated period of rotation is about 24 days.[5]

Planetary systemEdit

Animation of the planetary system

On August 24, 2010, a research team led by Christophe Lovis of the University of Geneva announced that the star has at least five planets, and possibly as many as seven.[5][12] The planets were detected using the HARPS spectrograph, in conjunction with the ESO's 3.6 m telescope at La Silla Observatory in Chile, using Doppler spectroscopy.

On April 5, 2012, astronomer Mikko Tuomi of the University of Hertfordshire submitted a paper to Astronomy and Astrophysics approved for publishing on the April 6, 2012 that proposed a nine planet model for the system. Re-analysing the data using Bayesian probability analysis, previously known planets' parameters were revised and further evidence was found for the innermost planet (b) as well as evidence of two additional planets (i and j).

The system is not known to be a transiting planetary system and as such planets are unlikely to be detected or verified by the transit method.

Orbital arrangementEdit

Orbits of the HD 10180 planetary system, using the orbital configuration from an eight-body (the star and seven planets) Newtonian model taking into account tidal dissipation.[note 2]

The system contains five planets with minimum masses from 12 to 25 times Earth's (comparable to the mass of Uranus and Neptune) at orbital radii of 0.06, 0.13, 0.27, 0.49 and 1.42 AU just short of that of Mars.

There are no planets known to be in mean-motion resonances, although it has a number of near resonances[5] including 3c:2i:1d and 3e:2j:1f. The approximate ratios of periods of adjacent orbits are (proceeding outward): 1:5, 1:3, 1:3, 2:5, 1:5, 3:11.

Since the inclination of the planets' orbits is unknown, only minimum planetary masses can presently be obtained. Dynamical simulations suggest that the system cannot be stable if the true masses of the planets exceed the minimum masses by a factor of greater than three (corresponding to an inclination of less than 20°, where 90° is edge-on).[5]


Artist's impression of HD 10180 d. Also depicted are planets b and c in transit.

HD 10180 b is a possible Earth-sized planet (minimum mass 1.4 times Earth's) located at 0.02 AU. Its orbital radius was originally estimated to have a near circular orbit at a distance of 0.02225 ± 0.00035 AU (closer than Mercury, about one seventh the distance and correspondingly hotter), taking 1.1 days to complete a full orbit.[13] Planet b was confirmed in 2012 with a slightly smaller orbital radius and a more eccentric orbit. The false detection probability was initially 1.4%;[5] however, its probability was firmed by Mikko Tuomi in 2012.

HD 10180 c, with a minimum mass comparable to that of Uranus, is a hot Neptune. Dynamical simulations suggest that if the mass gradient was any more than a factor of two, the system would not be stable. Planet c's orbital period and eccentricity were originally estimated at 5.75979 ± 0.00062 and 0.045 ± 0.026 respectively; however, these were revised in 2012 in favour of a more eccentric orbit. The false detection probability is less than 0.1%.[5]

HD 10180 i is a possible but unconfirmed hot super-Earth discovered by Mikko Tuomi in 2012.

HD 10180 d is a hot Neptune. Its mass was initially estimated at >11.75 ± 0.65 (smaller than Uranus) and on a slightly eccentric orbit; however, this was re-estimated with a larger mass and less eccentric orbit in 2012.

HD 10180 e is also a hot Neptune with about twice the mass of Neptune. Its estimated orbital distance and eccentricity were downscaled in 2012. The false detection probability is less than 0.1%.[5]

HD 10180 j is a possible but unconfirmed hot super-Earth or gas dwarf discovered by Mikko Tuomi in 2012.

HD 10180 f is a hot Neptune and of similar in mass to HD 10180 e. At orbital distance of 0.49AU and eccentricity of 0.13, its tight and wild orbit is analogous to that of Mercury with a similar black-body-temperature range though with its immense mass, any greenhouse effect caused by an atmosphere would give it searing Venus-like or greater temperatures. Estimated orbital distance and eccentricity were downscaled slightly in 2012. The false detection probability is less than 0.1%.[5]

HD 10180 g is a giant planet with a mass larger than Neptune's. It has a fairly circular orbit at 1.4 AU and therefore fully within the system's predicted habitable zone[14] though it does not fit the current models for planetary habitability due to its large mass (24 times Earth). If it is a gas giant, it is likely of Sudarsky Class II. There is a possibility that a natural satellite with sufficient atmospheric pressure could have liquid water on its surface. Its estimated orbital distance and eccentricity were downscaled in 2012 but remains in the habitable zone. The false detection probability is less than 0.1%.[5]

HD 10180 h is the largest and outermost known planet in the system. It is likely a Saturn-sized giant planet with a minimum mass 65 times that of Earth. Orbiting at 3.4 AU, a distance comparable to the distance of the outer part of the asteroid belt from the Sun and as such it is likely a Sudarsky Class I planet. The spurious detection probability is 0.6%.

The HD 10180 planetary system[8]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b >1.3 ± 0.8 M 0.02222 ± 0.00011 1.17766 ± 0.00022 0.0005 ± 0.0049
c >13.0 ± 2.0 M 0.0641 ± 0.0010 5.75973 ± 0.00083 0.07 ± 0.08
i (unconfirmed) >1.9 ± 1.8 M 0.0904 ± 0.047 9.655 ± 0.072 0.05 ± 0.23
d >11.9 ± 2.15 M 0.1284 ± 0.0061 16.354 ± 0.0013 0.011 ± 0.013
e >25.0 ± 3.9 M 0.270 ± 0.0013 49.75 ± 0.007 0.001 ± 0.010
j (unconfirmed) >5.1 ± 3.2 M 0.330 ± 0.016 67.55 ± 1.28 0.07 ± 0.12
f >23.9 ± 1.4 M 0.4929 ± 0.0078 122.88 ± 0.65 0.13 ± 0.015
g >21.4 ± 3.4 M 1.415 ± 0.091 596 ± 37 0.03 ± 0.40
h >65.8 ± 12.9 M 3.49 ± 0.60 2300 ± 550 0.18 ± 0.016

See alsoEdit

  • Kepler-90 A star with eight known planets (the first known to have an equal number of planets as the solar system).
  • TRAPPIST-1 A star with seven known planets.


  1. ^ For [Fe/H] equal to 0.08, the proportion is given by:
    100.08 = 1.20
    or 120%.
  2. ^ The parameters are taken from the Newtonian fit taking into account tidal dissipation given in table 6 of Lovis et al. (2010). A purely Keplerian solution with slightly different parameters is given in table 3 of the same paper.


  1. ^ a b c d e van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. ^ a b "HD 10180 -- Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2010-08-24.
  3. ^ a b Nordström, B.; et al. (May 2004). "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs". Astronomy and Astrophysics. 418 (3): 989–1019. arXiv:astro-ph/0405198. Bibcode:2004A&A...418..989N. doi:10.1051/0004-6361:20035959.
  4. ^ a b Takeda, Genya; Ford, Eric B.; Sills, Alison; Rasio, Frederic A.; Fischer, Debra A.; Valenti, Jeff A. (2007). "Structure and Evolution of Nearby Stars with Planets. II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog". The Astrophysical Journal Supplement Series. 168 (2): 297. arXiv:astro-ph/0607235. Bibcode:2007ApJS..168..297T. doi:10.1086/509763.
  5. ^ a b c d e f g h i j k l m Lovis, C; et al. (August 8, 2010). "The HARPS search for southern extra-solar planets XXVII. Up to seven planets orbiting HD 10180: probing the architecture of low-mass planetary systems". Astronomy & Astrophysics. 528: A112. arXiv:1011.4994. Bibcode:2011A&A...528A.112L. doi:10.1051/0004-6361/201015577.
  6. ^ a b c Sousa, S. G.; et al. (August 2007), "Spectroscopic parameters for 451 stars in the HARPS GTO planet search program. Stellar [Fe/H] and the frequency of exo-Neptunes", Astronomy and Astrophysics, 487 (1): 373–381, arXiv:0805.4826, Bibcode:2008A&A...487..373S, doi:10.1051/0004-6361:200809698
  7. ^ Holmberg, J.; Nordström, B.; Andersen, J. (July 2009). "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics". Astronomy and Astrophysics Supplement Series. 501 (3): 941–947. arXiv:0811.3982. Bibcode:2009A&A...501..941H. doi:10.1051/0004-6361/200811191. Note: see VizieR catalogue V/130.
  8. ^ a b Tuomi, Mikko (6 April 2012). "Evidence for 9 planets in the 10180 system". Astronomy & Astrophysics. 543: A52. arXiv:1204.1254v1. Bibcode:2012A&A...543A..52T. doi:10.1051/0004-6361/201118518.
  9. ^ Gill, Victoria (August 24, 2010). "Rich exoplanet system discovered". BBC News. BBC. Retrieved August 24, 2010.
  10. ^ Sherrod, P. Clay; Koed, Thomas L. (2003). A Complete Manual of Amateur Astronomy: Tools and Techniques for Astronomical Observations. Astronomy Series. Courier Dover Publications. p. 9. ISBN 978-0-486-42820-8.
  11. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16
  12. ^ "Richest Planetary System Discovered: Up to seven planets orbiting a Sun-like star" (Press release). European Southern Observatory. August 24, 2010. Retrieved 2010-08-24.
  13. ^ Chang, Kenneth. "Kepler Telescope Detects Possible Earth-Size Planet", The New York Times, August 26, 2010. Accessed August 26, 2010.
  14. ^ "Solar System 2.0 (beta) - Planetary Habitability Laboratory @ UPR Arecibo".

External linksEdit