21900 Orus

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21900 Orus
Discovery [1]
Discovered by T. Kobayashi
Discovery site Ōizumi Obs.
Discovery date 9 November 1999
MPC designation (21900) Orus
Pronunciation /ˈɔːrəs/
Named after
Orus (Greek mythology)[2]
1999 VQ10 · 1998 VD18
Jupiter trojan[1][3]
(Greek camp)[4]
Orbital characteristics[1]
Epoch 16 February 2017 (JD 2457800.5)
Uncertainty parameter 0
Observation arc 18.49 yr (6,754 days)
Aphelion 5.3099 AU
Perihelion 4.9452 AU
5.1275 AU
Eccentricity 0.0356
11.61 yr (4,241 days)
0° 5m 5.64s / day
Inclination 8.4678°
Jupiter MOID 0.0159 AU
TJupiter 2.9770
Physical characteristics
Dimensions 50.810±0.809[5][6][7]
53.87±4.08 km[8]
55.67 km (calculated)[3]
13.45±0.08 h[9]
0.057 (assumed)[3]
C[3][10] · D[7]
9.80[8] · 9.9[5] · 10.0[1][3] · 10.12±0.32[10]

21900 Orus (/ˈɔːrəs/), provisional designation 1999 VQ10, is a carbonaceous Jupiter trojan of the Greek camp, approximately 53 kilometers in diameter. It is a target to be visited by the Lucy mission in November 2028.[7]

This asteroid was discovered on 9 November 1999, by Japanese amateur astronomer Takao Kobayashi at his private Ōizumi Observatory in Gunma Prefecture, Japan, and later named after the Achaean warrior Orus from Greek mythology.[2]

Orbit and classification[edit]

Orus is a carbonaceous asteroid that is located in the Greek camp of Jupiter's leading L4 Lagrangian point. It orbits the Sun at a distance of 4.9–5.3 AU once every 11 years and 7 months (4,241 days). Its orbit has an eccentricity of 0.04 and an inclination of 8° with respect to the ecliptic.[1] The first precovery was taken by the Digitized Sky Survey at Palomar Observatory in 1951, extending the body's observation arc by 48 years prior to its official discovery observation.[2]

Physical characteristics[edit]

Orus is characterized as a D-type and C-type asteroid by the Lucy mission team and by PanSTARRS photometric survey, respectively.[7][10]


In October 2009, Orus was observed by astronomer Stefano Mottola in a photometric lightcurve survey of 80 Jupiter trojans, using the 1.2-meter telescope at Calar Alto Observatory. The obtained rotational lightcurve rendered a period of 13.45±0.08 hours with a brightness variation of 0.18 magnitude (U=2).[9]

Diameter and albedo[edit]

According to the surveys carried out by the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, the body has an albedo of 0.083 and 0.075, with a diameter of 53.87 and 50.81 kilometers, respectively.[5][6][8] The Collaborative Asteroid Lightcurve Link assumes a standard albedo for carbonaceous C-type asteroids of 0.057 and calculates a diameter of 55.67 kilometers with an absolute magnitude of 10.0.[3]


This minor planet was named from Greek mythology after Orus, an Achaean warrior in Homer's Iliad. He was killed in the Trojan War by the Trojan prince Hector, after whom the largest Jupiter trojan 624 Hektor is named.[2] The approved naming citation was published by the Minor Planet Center on 22 February 2016 (M.P.C. 98711).[11]

Lucy mission target[edit]

Orus is planned to be visited by the Lucy spacecraft which will launch in 2021. The fly by is scheduled for 20 November 2028, and will approach the asteroid to a distance of 1000 kilometers at a velocity of 7.1 kilometers per second.[7] The mission's targets with their flyby dates are:[7][12][13]

  1. 52246 Donaldjohanson — 20 April 2025: 4 km diameter C-type asteroid in the inner main-belt, member of ~130Myr old Erigone family;
  2. 3548 Eurybates — 12 August 2027: 64 km diameter C-type Jupiter Trojan in the Greek camp at L4, largest member of the only confirmed disruptive collisional family in the Trojans;
  3. 15094 Polymele — 15 September 2027: 21 km diameter P-type Trojan at L4, likely collisional fragment;
  4. 11351 Leucus — 18 April 2028: 34 km diameter D-type slow rotator Trojan at L4;
  5. 21900 Orus — 11 November 2028: 51 km diameter D-type Trojan at L4;
  6. 617 Patroclus — 2 March 2033: P-type binary Trojan. The primary, Patroclus, has a mean diameter of 113 km and its companion, Menoetius, has a diameter of 104 km. The pair orbit at a separation of 680 km. The binary resides in the Trojan camp at L5.

See also[edit]


  1. ^ a b c d e "JPL Small-Body Database Browser: 21900 Orus (1999 VQ10)" (2017-05-08 last obs.). Jet Propulsion Laboratory. Retrieved 5 July 2017. 
  2. ^ a b c d "21900 Orus (1999 VQ10)". Minor Planet Center. Retrieved 26 May 2016. 
  3. ^ a b c d e f "LCDB Data for (21900) Orus". Asteroid Lightcurve Database (LCDB). Retrieved 26 May 2016. 
  4. ^ "List of Jupiter Trojans". Minor Planet Center. 20 June 2016. Retrieved 4 December 2016. 
  5. ^ a b c d Mainzer, A.; Grav, T.; Masiero, J.; Hand, E.; Bauer, J.; Tholen, D.; et al. (November 2011). "NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results". The Astrophysical Journal. 741 (2): 25. arXiv:1109.6407Freely accessible. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90. Retrieved 26 May 2016. 
  6. ^ a b c Grav, T.; Mainzer, A. K.; Bauer, J. M.; Masiero, J. R.; Nugent, C. R. (November 2012). "WISE/NEOWISE Observations of the Jovian Trojan Population: Taxonomy". The Astrophysical Journal. 759 (1): 10. arXiv:1209.1549Freely accessible. Bibcode:2012ApJ...759...49G. doi:10.1088/0004-637X/759/1/49. Retrieved 5 December 2016. 
  7. ^ a b c d e f Levison, H. F.; Olkin, C.; Noll, K. S.; Marchi, S.; Lucy Team (March 2017). "Lucy: Surveying the Diversity of the Trojan Asteroids: The Fossils of Planet Formation" (PDF). 48th Lunar and Planetary Science Conference. Bibcode:2017LPI....48.2025L. Retrieved 13 April 2017. 
  8. ^ a b c d Usui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi; et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117. Retrieved 26 May 2016. 
  9. ^ a b Mottola, Stefano; Di Martino, Mario; Erikson, Anders; Gonano-Beurer, Maria; Carbognani, Albino; Carsenty, Uri; et al. (May 2011). "Rotational Properties of Jupiter Trojans. I. Light Curves of 80 Objects". The Astronomical Journal. 141 (5): 32. Bibcode:2011AJ....141..170M. doi:10.1088/0004-6256/141/5/170. Retrieved 26 May 2016. 
  10. ^ a b c Veres, Peter; Jedicke, Robert; Fitzsimmons, Alan; Denneau, Larry; Granvik, Mikael; Bolin, Bryce; et al. (November 2015). "Absolute magnitudes and slope parameters for 250,000 asteroids observed by Pan-STARRS PS1 - Preliminary results". Icarus. 261: 34–47. arXiv:1506.00762Freely accessible. Bibcode:2015Icar..261...34V. doi:10.1016/j.icarus.2015.08.007. Retrieved 26 May 2016. 
  11. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 26 May 2016. 
  12. ^ Dreier, Casey; Lakdawalla, Emily (30 September 2015). "NASA announces five Discovery proposals selected for further study". The Planetary Society. Retrieved 1 February 2016. 
  13. ^ https://www.hou.usra.edu/meetings/lpsc2017/pdf/2025.pdf

External links[edit]