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162173 Ryugu, provisional designation 1999 JU3, is a near-Earth object and a potentially hazardous asteroid of the Apollo group. It measures approximately 1 kilometer (0.6 mi) in diameter and is a dark object of the rare spectral type Cg, with qualities of both a C-type asteroid and a G-type asteroid. In June 2018, a spacecraft, Hayabusa2, arrived at the asteroid.

162173 Ryugu
162173 Ryugu.jpg
Monochrome view of Ryugu[a]
Discovery [1]
Discovered byLINEAR
Discovery siteLincoln Lab's ETS
Discovery date10 May 1999
MPC designation(162173) Ryugu
Named after
("Dragon palace")
1999 JU3
Apollo · NEO · PHA[1][2]
Orbital characteristics[2]
Epoch 12 December 2011 (JD 2455907.5)
Uncertainty parameter 0
Observation arc30.32 yr (11,075 d)
Aphelion1.4159 AU
Perihelion0.9633 AU
1.1896 AU
1.30 yr (474 d)
0° 45m 34.56s / day
Earth MOID0.0006 AU (0.2337 LD)
Physical characteristics
Mean diameter
0.865±0.015 km[3]
0.87 km[4]
0.90±0.14 km[5]
0.92±0.12 km[6]
0.980±0.029 km[7]
1.13±0.03 km[8]
Mass4.5×1011 kg[9]
Equatorial surface gravity
1/80,000 g[9]
7.627±0.007 h[7][10]
SMASS = Cg[2] · C[3]
18.69±0.07 (R)[4]



Discovery and nameEdit

Ryugu was discovered on 10 May 1999 by astronomers with the Lincoln Near-Earth Asteroid Research at the Lincoln Lab's ETS near Socorro, New Mexico, in the United States. It was given the provisional designation 1999 JU3.[1] The asteroid was officially named "Ryugu" by the Minor Planet Center on 28 September 2015 (M.P.C. 95804).[11] The name refers to Ryūgū (Dragon Palace), a magical underwater palace in a Japanese folktale. In the story, the fisherman Urashima Tarō travels to the palace on the back of a turtle, and when he returns, he carries with him a mysterious box, much like Hayabusa2 returning with samples.[1][12]


Orbit between Earth and Mars


Ryugu orbits the Sun at a distance of 0.96–1.41 au once every 16 months (474 days; semi-major axis of 1.19 au). Its orbit has an eccentricity of 0.19 and an inclination of 6° with respect to the ecliptic.[2] It has a minimum orbital intersection distance with Earth of 95,400 km (0.000638 au), which translates into 0.23 lunar distance.[2]


Early analysis in 2012 by Thomas G. Müller et al. used data from a number of observatories, and suggested that the asteroid was "almost spherical", a fact that hinders precise conclusions, with retrograde rotation, an effective diameter of 0.85–0.88 kilometers, and a geometric albedo of 0.044 to 0.050. They estimated that the grain sizes of its surface materials are between 1 and 10 mm.[3]

Initial images taken by the Hayabusa2 spacecraft on approach at a distance of 700 km were released on 14 June 2018. They revealed a diamond shaped body and confirmed its retrograde rotation.[13] Between 17 and 18 June 2018, Hayabusa2 went from 330 km to 240 km from Ryugu and captured a series of additional images from the closer approach.[14] Astronomer Brian May created stereoscopic images from data collected a few days later.[15]

The acceleration due to gravity at the equator has been evaluated at about 0.11 mm/s2, or about 0.0001 m/sec2. It rises to 0.15 mm/s2 at the poles. The mass of Ryugu is estimated at about 450 million tons.[16]

Value and compositionEdit

As of May 2018, according to the Asterank website, operated by Planetary Resources, the current value of Ryugu for mining purposes is speculated to be US$82.76 billion, and the chemical composition of the asteroid was estimated based on its class before Hayabusa 2 to be of nickel, iron, cobalt, water, nitrogen, hydrogen and ammonia.[17]

Hayabusa2 missionEdit

Animation of Hayabusa2 orbit from 3–29 December 2019
  Hayabusa2   162173 Ryugu   Earth   Sun

The Japan Aerospace Exploration Agency (JAXA) spacecraft Hayabusa2 was launched in December 2014 and successfully arrived at the asteroid on 27 June 2018. It is planned to return material from the asteroid to Earth by December 2020.[18]

The Hayabusa2 mission includes four rovers with various scientific instruments. On 21 September 2018, the first two of these rovers, which hop around the surface of the asteroid, were released from Hayabusa2.[19] This marks the first time a mission has completed a successful landing on a fast-moving asteroid body.[20]

On 3 October 2018, the German-French Mobile Asteroid Surface Scout (MASCOT) lander successfully arrived on Ryugu, 10 days after the MINERVA rovers landed.[21] Its mission was short-lived, however, with only 16 hours available from its batteries.

See alsoEdit



  1. ^ Photograph of the full disc of 162173 Ryugu by the Optical Navigation Camera – Telescopic (ONC-T) instrument aboard the Hayabusa2 spacecraft. The photograph was taken on 26 June 2018, at a distance of 20 kilometres (12 miles) from the asteroid's surface.


  1. ^ a b c d e f "162173 Ryugu (1999 JU3)". Minor Planet Center. Retrieved 30 October 2018.
  2. ^ a b c d e f "JPL Small-Body Database Browser: 162173 Ryugu (1999 JU3)" (2016-08-09 last obs.). Jet Propulsion Laboratory. Retrieved 30 October 2018.
  3. ^ a b c d e Müller, T. G.; Durech, J.; Ishiguro, M.; Mueller, M.; Krühler, T.; Yang, H.; et al. (March 2017). "Hayabusa-2 mission target asteroid 162173 Ryugu (1999 JU3): Searching for the object's spin-axis orientation" (PDF). Astronomy and Astrophysics. 599: 25. arXiv:1611.05625. Bibcode:2017A&A...599A.103M. doi:10.1051/0004-6361/201629134. Retrieved 30 October 2018.
  4. ^ a b c Kim, Myung-Jin; Choi, Young-Jun; Moon, Hong-Kyu; Ishiguro, Masateru; Mottola, Stefano; Kaplan, Murat; et al. (February 2013). "Optical observations of NEA 162173 (1999 JU3) during the 2011-2012 apparition" (PDF). Astronomy and Astrophysics. 550: 4. arXiv:1302.4542. Bibcode:2013A&A...550L..11K. doi:10.1051/0004-6361/201220673. Retrieved 30 October 2018.
  5. ^ a b Campins, H.; Emery, J. P.; Kelley, M.; Fernández, Y.; Licandro, J.; Delbó, M.; et al. (August 2009). "Spitzer observations of spacecraft target 162173 (1999 JU3)" (PDF). Astronomy and Astrophysics. 503 (2): L17–L20. arXiv:0908.0796. Bibcode:2009A&A...503L..17C. doi:10.1051/0004-6361/200912374. Retrieved 30 October 2018.
  6. ^ a b c Hasegawa, S.; Müller, T. G.; Kawakami, K.; Kasuga, T.; Wada, T.; Ita, Y.; et al. (December 2008). "Albedo, Size, and Surface Characteristics of Hayabusa-2 Sample-Return Target 162173 1999 JU3 from AKARI and Subaru Observations". Publications of the Astronomical Society of Japan. 60 (SP2): S399––S405. Bibcode:2008PASJ...60S.399H. doi:10.1093/pasj/60.sp2.S399. Retrieved 30 October 2018.
  7. ^ a b c d Abe, M.; Kawakami, K.; Hasegawa, S.; Kuroda, D.; Yoshikawa, M.; Kasuga, T.; et al. (March 2008). "Ground-based Observational Campaign for Asteroid 162173 1999 JU3" (PDF). Lunar and Planetary Science: 1594. Bibcode:2008LPI....39.1594A. Retrieved 30 October 2018.
  8. ^ a b Yu, Liang-Liang; Ji, Jiang-Hui; Wang, Su (July 2014). "Investigation of Thermal Inertia and Surface Properties for Near-earth Asteroid (162173) 1999 JU3". Chinese Astronomy and Astrophysics. 38 (3): 317–329. Bibcode:2014ChA&A..38..317L. doi:10.1016/j.chinastron.2014.07.008. Retrieved 30 October 2018.
  9. ^ a b Clark, Stephen (6 September 2018). "Hayabusa 2 team sets dates for asteroid landings – Spaceflight Now". Retrieved 7 September 2018.
  10. ^ "LCDB Data for (162173) Ryugu". Asteroid Lightcurve Database (LCDB). Retrieved 30 October 2018.
  11. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 30 October 2018.
  12. ^ "Name Selection of Asteroid 1999 JU3 Target of the Asteroid Explorer "Hayabusa2"" (Press release). JAXA. 5 October 2015. Retrieved 30 October 2018.
  13. ^ "From a distance of about 700km, Ryugu's rotation was observed". JAXA. 16 June 2016. Retrieved 30 October 2018.
  14. ^ Plait, Phil (20 June 2018). "Asteroid Ryugu Starts to Come Into Focus". SyFy Wire. Retrieved 30 October 2018.
  15. ^ Bartels, Meghan (10 July 2018). "Queen's Brian May Will Rock You with This Stereo Image of Asteroid Ryugu". Retrieved 24 December 2018.
  16. ^ Operation status for the asteroid explorer, Hayabusa2, in the vicinity of Ryugu (PDF), JAXA, 5 September 2018, retrieved 30 October 2018
  17. ^, Value: 82.76 billion Estimated profit: 30.07 billion
  18. ^ "Current status of the asteroid explorer, Hayabusa2, leading up to arrival at asteroid Ryugu in 2018" (PDF). JAXA. 14 June 2016. Retrieved 30 October 2018.
  19. ^ Wall, Mike (21 September 2018). "Japanese Probe Deploys Tiny Hopping Robots Toward Big Asteroid Ryugu". Retrieved 30 October 2018.
  20. ^ Yoshimitsu, Tetsuo; Kubota, Takashi; Tsuda, Yuichi; Yoshikawa, Makoto (23 September 2015). "MINERVA-II1: Successful image capture, landing on Ryugu and hop!". JAXA Hayabusa2 Project. JAXA. Retrieved 30 October 2018.
  21. ^ "Touchdown! Japan space probe lands new robot on asteroid". 3 October 2018. Retrieved 30 October 2018.


External linksEdit