162173 Ryugu
162173 Ryugu (provisional designation 1999 JU3) is a near-Earth object and a potentially hazardous asteroid of the Apollo group. It measures approximately 900 metres (3,000 ft) in diameter and is a dark object of the rare spectral type Cb, with qualities of both a C-type asteroid and a B-type asteroid. In June 2018, the Japanese spacecraft Hayabusa2 arrived at the asteroid. After making measurements and taking samples, Hayabusa2 left Ryugu for Earth in November 2019 and returned the sample capsule to Earth on 5 December 2020. The samples showed the presence of organic compounds, such as uracil (one of the four components in RNA) and vitamin B3.
Color image of Ryugu taken by Hayabusa2, 2018 | |
| Discovery | |
|---|---|
| Discovered by | LINEAR |
| Discovery site | Lincoln Lab's ETS |
| Discovery date | 10 May 1999 |
| Designations | |
MPC designation | (162173) Ryugu |
| Pronunciation | /riˈuːɡuː/ Japanese: [ɾjɯːɡɯː] |
Named after | Ryūgū ("Dragon palace") |
Alternative designations | 1999 JU3 |
Minor planet category | Apollo · NEO · PHA |
| Orbital characteristics | |
| 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 |
Semi-major axis | 1.1896 AU |
| Eccentricity | 0.1902 |
Orbital period (sidereal) | 1.30 yr (474 d) |
Mean anomaly | 3.9832° |
Mean motion | 0° 45m 34.56s / day |
| Inclination | 5.8837° |
Longitude of ascending node | 251.62° |
| 211.43° | |
| Earth MOID | 0.0006 AU (0.2337 LD) |
| Physical characteristics | |
| Dimensions | 1004 m × 876 m |
Mean radius | 448±2 m |
Equatorial radius | 502±2 m |
Polar radius | 438±2 m |
| Volume | 0.377±0.005 km3 |
| Mass | (4.50±0.06)×1011 kg |
Mean density | 1.19±0.03 g cm−3 |
Equatorial surface gravity | 1/80,000 g |
Synodic rotation period | 7.63262±0.00002 h |
| 171.64°±0.03° | |
North pole right ascension | +96.40°±0.03° |
North pole declination | −66.40°±0.03° |
| 0.037±0.002 0.042±0.003 0.047±0.003 0.063±0.020 0.07±0.01 0.078±0.013 | |
| SMASS = Cg · C · Cb | |
| 18.69±0.07 (R) 18.82 19.2 19.25±0.03 19.3 | |
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