 Shape model of Orus viewed from multiple orthogonal perspectives | |
| Discovery[1] | |
|---|---|
| Discovered by | T. Kobayashi |
| Discovery site | Ōizumi Obs. |
| Discovery date | 9 November 1999 |
| Designations | |
| (21900) Orus | |
| Pronunciation | /ˈɔːrəs/[2] |
Named after | Orus(Greek mythology)[1] |
| 1999 VQ10 · 1998 VD18 | |
| Jupiter trojan[1][3] Greek[4] · background[5] | |
| Adjectives | Orian |
| Orbital characteristics[3] | |
| Epoch 25 February 2023 (JD 2460000.5) | |
| Uncertainty parameter 0 | |
| Earliestprecovery date | 8 November 1951 |
| Aphelion | 5.124AU |
| Perihelion | 4.930 AU |
| 5.318 AU | |
| Eccentricity | 0.0379 |
| 11.60 yr (4,237 d) | |
| 356.275° | |
| 0° 5m 5.892s / day | |
| Inclination | 8.469° |
| 258.554° | |
| 181.258° | |
| Jupiter MOID | 0.0218 AU |
| TJupiter | 2.977 |
| Physical characteristics | |
| Dimensions | 70.7 × 63.0 × 51.4 km[6] |
| 60.5±0.9 km (area equivalent)[6] | |
| 13.486190±0.000017 h[6] | |
| 149° (wrtecliptic)[6] 154° (wrt orbit)[6] | |
| 33°[6] | |
| −59°[6] | |
| 0.040±0.002[6] | |
| C[7][8] · D[9] B–V =0.799±0.031[6] V–R =0.454±0.021[6] | |
| 10.204±0.006[6] | |
21900 Orus/ˈɔːrəs/ is aJupiter trojanasteroid from theGreek camp, approximately 53 kilometers (33 miles) in diameter, and a target of theLucy mission to be visited in November 2028.[9] It is among the100 largest Jupiter trojans and has arotation period of 13.5 hours.[7] It was discovered on 9 November 1999, by Japanese amateur astronomerTakao Kobayashi at his privateŌizumi Observatory in Gunma Prefecture, Japan, and later named Orus after a slainAchaean warrior from theIliad.[1]
Orus is a darkJupiter trojanasteroid orbiting in the leading Greek camp at Jupiter'sL4Lagrangian point, 60° ahead of its orbit in a1:1 resonance(seeTrojans in astronomy). It is also a non-family asteroid in theJovian background population.[5]
It orbits the Sun at a distance of 4.9–5.3 AU once every 11 years and 7 months (4,240 days;semi-major axis of 5.13 AU). Its orbit has aneccentricity of 0.04 and aninclination of 8° with respect to theecliptic.[3] The body'sobservation arc begins with aprecovery, published by theDigitized Sky Survey and taken atPalomar Observatory in November 1951, or 48 years prior to its official discovery observation.[1]
Orus is planned to be visited by theLucy spacecraft which was launched in 2021. Theflyby is scheduled for 11 November 2028, and will approach the asteroid to a distance of 1,000 km (620 mi) at a relative velocity of 7.1 km/s (16,000 mph).[9]
Orus is characterized as aD-type andC-type asteroid by theLucy mission team and byPan-STARRS photometric survey, respectively.[9][8] It has aV–I color index of 0.95, seem among most larger D-type Jupiter trojans.[7]
The first photometric observations of Orus have been made in October 2009, by astronomerStefano Mottola in a photometriclightcurve survey of 80 Jupiter trojans, using the 1.2-meter telescope atCalar Alto Observatory. The obtained rotational lightcurve rendered aperiod of13.45±0.08 hours with a brightness variation of 0.18magnitude (U=2).[7][10]
In 2016, Mottola published a revised rotation period of13.48617±0.00007 h, from ground-based observations taken over five apparitions in support of theLucy mission. He finds that Orus is a retrograde rotator. The lightcurve suggests the presence of a large crater in the proximity of its north pole.[11]
According to the surveys carried out by the JapaneseAkari satellite and theNEOWISE mission of NASA'sWide-field Infrared Survey Explorer, the body has analbedo of 0.083 and 0.075, with a diameter of 53.87 and 50.81 kilometers, respectively.[12][13] TheCollaborative Asteroid Lightcurve Link assumes a standard albedo for carbonaceous C-type asteroids of 0.057 and calculates a diameter of 55.67 kilometers with anabsolute magnitude of 10.0.[7]
Thisminor planet was named fromGreek mythology after Orus, anAchaean warrior in Homer'sIliad. He was killed in theTrojan War by the Trojan princeHector, after whom the largest Jupiter trojan624 Hektor is named.[1] The approved naming citation was published by theMinor Planet Center on 22 February 2016 (M.P.C. 98711).[14]
Orus has a candidate satellite, detected while searching through Hubble images taken on 7–8 August 2018.[16] Further observations are needed to determine physical characteristics of the satellite, which can help measure the mass of the primary.
