162173 Ryugu

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162173 Ryugu
162173 Ryugu.jpg
Monochrome view of Ryugu[a]
Discovery [1]
Discovered by LINEAR
Discovery site Lincoln Lab's ETS
Discovery date 10 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 arc 30.32 yr (11,075 d)
Aphelion 1.4159 AU
Perihelion 0.9633 AU
1.1896 AU
Eccentricity 0.1902
1.30 yr (474 d)
0° 45m 34.56s / day
Inclination 5.8837°
Earth MOID 0.0006 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]
Mass 496×106 tons[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]

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.



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.[1] It was given the provisional designation 1999 JU3.


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
Animation of Hayabusa2 orbit from 3 December 2014 to 29 December 2019
  Hayabusa2   162173 Ryugu   Earth   Sun

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 Hayabusa-2 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, Hayabusa 2 went from 330 km to 240 km from Ryugu and captured a series of additional images from the closer approach.[14]

Value and composition[edit]

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.[15]

Hayabusa2 mission[edit]

The Japan Aerospace Exploration Agency (JAXA) spacecraft Hayabusa 2 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 the end of 2020.[16]

The Hayabusa2 mission includes four rovers with various scientific instruments. On 21 September 2018, the first two of these rovers, which will hop around the surface of the asteroid, were released from Hayabusa2.[17].

On September 22, 2018, JAXA confirmed the two rovers had successfully touched down on Ryugu's surface. Three images were published; two during descent to the asteroid and one after MINERVA-II1A touched down. This marks the first time a mission has completed a successful landing on a fast-moving asteroid body.

See also[edit]



  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 22 June 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 22 June 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". Astronomy and Astrophysics. 599: 25. arXiv:1611.05625Freely accessible. Bibcode:2017A&A...599A.103M. doi:10.1051/0004-6361/201629134. 
  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". Astronomy and Astrophysics. 550 (11): 4. arXiv:1302.4542Freely accessible. Bibcode:2013A&A...550L..11K. doi:10.1051/0004-6361/201220673. 
  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)". Astronomy and Astrophysics. 503 (2): L17–L20. arXiv:0908.0796Freely accessible. Bibcode:2009A&A...503L..17C. doi:10.1051/0004-6361/200912374. 
  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 22 June 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). 37th COSPAR Scientific Assembly. Lunar and Planetary Science. 39. p. 1594. Bibcode:2008LPI....39.1594A. Retrieved 22 June 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. arXiv:1805.05244Freely accessible. Bibcode:2014ChA&A..38..317Y. doi:10.1016/j.chinastron.2014.07.008. Retrieved 22 June 2018. 
  9. ^ a b Clark, Stephen (6 September 2018). "Hayabusa 2 team sets dates for asteroid landings – Spaceflight Now". spaceflightnow.com. Retrieved 7 September 2018. 
  10. ^ "LCDB Data for (162173) Ryugu". Asteroid Lightcurve Database (LCDB). Retrieved 22 June 2018. 
  11. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 22 June 2018. 
  12. ^ "Name Selection of Asteroid 1999 JU3 Target of the Asteroid Explorer "Hayabusa2"" (Press release). JAXA. 5 October 2015. Retrieved 22 June 2018. 
  13. ^ "From a distance of about 700km, Ryugu's rotation was observed". JAXA. Retrieved 18 June 2018. 
  14. ^ Plait, Phil, "Asteroid Ryugu Starts to Come Into Focus", SyFy Wire, 20 June 2018. Accessed 20 June 2018.
  15. ^ http://www.asterank.com/, Value: 82.76 billion Estimated profit: 30.07 billion
  16. ^ "Current status of the asteroid explorer, Hayabusa2, leading up to arrival at asteroid Ryugu in 2018" (PDF). JAXA. Retrieved 18 June 2018. 
  17. ^ Wall, Mike. "Japanese Probe Deploys Tiny Hopping Robots Toward Big Asteroid Ryugu". SPACE.COM. Retrieved 21 September 2018. 


External links[edit]