| Discovery[1] | |
|---|---|
| Discovered by | David H. Levy and Henry Holt |
| Discovery date | 20 June 1990 |
| Designations | |
| Pronunciation | /jʊˈriːkə/yuurr-EE-kə[2] |
Named after | Eureka |
| 1990 MB | |
Martian L5 | |
| Orbital characteristics[3] | |
| Epoch 13 January 2016 (JD 2457400.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 13267 days (36.32 yr) |
| Aphelion | 1.6222 AU (242.68 Gm) |
| Perihelion | 1.4249 AU (213.16 Gm) |
| 1.5236 AU (227.93 Gm) | |
| Eccentricity | 0.064766 |
| 1.88yr (686.89d) | |
Averageorbital speed | 24.11 km/s |
| 145.29° | |
| 0° 31m 26.76s / day | |
| Inclination | 20.280° |
| 245.057° | |
| 95.456° | |
| Knownsatellites | 1 |
| Earth MOID | 0.497052 AU (74.3579 Gm) |
| Jupiter MOID | 3.52162 AU (526.827 Gm) |
| TJupiter | 4.428 |
| Physical characteristics | |
| Dimensions | 1.3[4] km ~2–4 kmH |
| 2.6902 h (0.11209 d) | |
| 0.39[4] | |
| Temperature | ~250[4] K |
| S(I)[4] (Gaffey) | |
| 16.0,[4] 16.1[3] | |
5261 Eureka is the firstMars trojan discovered.[5] It was discovered byDavid H. Levy and Henry Holt atPalomar Observatory on 20 June 1990.[1] It trailsMars (at theL5 point) at a distance varying by only 0.3AU during each revolution (with asecular trend superimposed, changing the distance from 1.5–1.8 AU around 1850 to 1.3–1.6 AU around 2400). Minimum distances fromEarth,Venus, andJupiter, are 0.5, 0.8, and 3.5 AU, respectively.
Long-termnumerical integration shows that the orbit is stable.Kimmo A. Innanen andSeppo Mikkola note that "contrary to intuition, there is clearempirical evidence for the stability of motion around theL4 andL5 points of all the terrestrial planets over a timeframe of several million years".
Since the discovery of 5261 Eureka, theMinor Planet Center has recognized three other asteroids as Martian trojans:(121514) 1999 UJ7 at theL4 point,(101429) 1998 VF31 at theL5 point,[5] and(311999) 2007 NS2, also at theL5 point.[6] At least five other asteroids in near-1:1resonances with Mars have been discovered, but they do not exhibit trojan behavior. They are2001 FR127,2001 FG24,(36017) 1999 ND43,1998 QH56 and(152704) 1998 SD4. Due to close orbital similarities, most of the other, smaller, members of the L5 group are hypothesized to be fragments of 5261 Eureka that were detached after it was spun up by theYORP effect (consistent with its rotational period of 2.69 h).[7]
Theinfrared spectrum for 5261 Eureka is typical for anA-type asteroid, but the visual spectrum is consistent with an evolved form ofachondrite called anangrite. A-class asteroids are tinted red in hue, with a moderatealbedo. The asteroid is located deep within a stable Lagrangian zone of Mars, which is considered indicative of a primordial origin—meaning the asteroid has most likely been in this orbit for much of the history of theSolar System.[citation needed]
| Discovery | |
|---|---|
| Discovery date | 28 November 2011 |
| Designations | |
Designation | S/2011 (5261) 1 |
| Orbital characteristics | |
| Epoch 9 December 2014 | |
| 2.1 km | |
| 0.7054 ± 0.0004 d | |
| Physical characteristics | |
| Dimensions | 0.46 km |
On 28 November 2011, anatural satellite of 5261 Eureka was found. This unnamed moon is about 0.46 km in diameter and orbits 2.1 km from Eureka. The satellite's existence was announced in September 2014.[8]
