162173 Ryugu

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162173 Ryugu
Discovered by LINEAR
Discovery date 10 May 1999
MPC designation (162173) Ryugu
Named after
1999 JU3
NEO · PHA · Apollo[1]
Orbital characteristics[1]
Epoch 13 January 2016 (JD 2457400.5)
Uncertainty parameter 0
Observation arc 9567 days (26.19 yr)
Aphelion 1.4158 AU (211.80 Gm)
Perihelion 0.96328 AU (144.105 Gm)
1.1895 AU (177.95 Gm)
Eccentricity 0.19021
1.30 yr (473.88 d)
Inclination 5.8836°
Earth MOID 0.000320643 AU (47,967.5 km)
Physical characteristics
Dimensions 0.82 km (est at 0.057)[2]
0.980±29 km[3]
7.627 h (0.3178 d)[1]
SMASS = Cg[1]
Animation of Hayabusa2 orbit from December 3, 2014 to December 9, 2019.
Purple: Hayabusa2; Lime: Ryugu; Blue: Earth; Yellow: Sun;

162173 Ryugu (provisional designation 1999 JU3), is an asteroid classified as a near-Earth object and as a potentially hazardous asteroid of the Apollo group. It measures nearly one kilometer 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 is the planned target of the Japanese space probe Hayabusa2, a sample return mission launched in late 2014. The probe is scheduled to reach Ryugu in June 2018, and to return material from the asteroid to Earth by the end of 2020.[4]



Ryugu was discovered in 1999 by the LINEAR project, and was given the provisional designation 1999 JU3.


The asteroid was officially named Ryugu on 5 October 2015,[5] the name refers to Ryūgū-jō (Dragon's 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.[5]



In 2012, T.G. Muller et al studied Ryugu using a variety of observatories, as well as reanalysing previous observations, they found that the asteroid is "almost spherical", a fact that hinders precise conclusions, but proposed that it probably has a retrograde rotation, an effective diameter of 850 to 880 m, and a geometric albedo of 0.044 to 0.050. They estimated that the grain sizes of its surface materials are 1 and 10 mm.[6]

Initial images taken from 700 km are released on June 14 2018, they show a diamond shape body and confirm its retrograde rotation.[7]


As of May 2018, the Asterank website, operated by Planetary Resources, speculates that the current value of Ryugu for mining purposes is US$82.76 billion.[8][full citation needed]

See also[edit]


  1. ^ a b c d "JPL Small-Body Database Browser: 162173 Ryugu (1999 JU3)". Jet Propulsion Laboratory. Retrieved 26 March 2016. 
  2. ^ "Asteroid Size Estimator". CNEOS NASA/JPL. Retrieved 12 November 2017. 
  3. ^ Hasegawa, S.; et al. (2008). "Albedo, Size, and Surface Characteristics of Hayabusa-2 Sample-Return Target 162173 1999 JU3 from AKARI". Publications of the Astronomical Society of Japan. 60 (SP2): S399–S405. Bibcode:2008PASJ...60S.399A. doi:10.1093/pasj/60.sp2.s399. 
  4. ^ "Current status of the asteroid explorer, Hayabusa2, leading up to arrival at asteroid Ryugu in 2018" (PDF). JAXA. Retrieved 18 June 2018. 
  5. ^ a b "Name Selection of Asteroid 1999 JU3 Target of the Asteroid Explorer "Hayabusa2"" (Press release). JAXA. October 5, 2015. Retrieved 2015-10-06. 
  6. ^ Muller, T.G.; 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. 
  7. ^ "From a distance of about 700km, Ryugu's rotation was observed". JAXA. Retrieved 18 June 2018. 
  8. ^ http://www.asterank.com/


External links[edit]