5261 Eureka
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| Discovery | |
|---|---|
| Discovered by: | David H. Levy |
| Discovery date: | June 20, 1990 |
| Alternative names: | 1990 MB |
| Minor planet category: | Mars-crosser asteroid |
| Orbital characteristics | |
| Epoch July 14, 2004 (JD 2453200.5) | |
| Aphelion distance: | 242.684 Gm (1.622 AU) |
| Perihelion distance: | 213.132 Gm (1.425 AU) |
| Semi-major axis: | 227.908 Gm (1.523 AU) |
| Eccentricity: | 0.065 |
| Orbital period: | 686.829 d (1.88 a) |
| Avg. orbital speed: | 24.11 km/s |
| Mean anomaly: | 104.086° |
| Inclination: | 20.280° |
| Longitude of ascending node: | 245.108° |
| Argument of perihelion: | 95.361° |
| Physical characteristics | |
| Dimensions: | ~2-4 km |
| Mass: | ? kg |
| Mean density: | ? g/cm³ |
| Equatorial surface gravity: | ? m/s² |
| Escape velocity: | ? km/s |
| Rotation period: | ? d |
| Albedo: | ? |
| Temperature: | ~225 K |
| Spectral type: | ? |
| Absolute magnitude: | 16.1 |
5261 Eureka was discovered at Mt Palomar on June 20, 1990 and turned out to be the first known Mars Trojan asteroid. It trails Mars (at the L5 point) at a distance varying by only 0.3 AU during each revolution (with a secular trend superimposed, changing the distance from 1.5-1.8 AU around 1850 to 1.3-1.6 AU around 2400). Minimum distances from the Earth, Venus and Jupiter are 0.5, 0.8 and 3.5 AU, respectively.
Long-term numerical integration shows that the orbit is stable. Kimmo A. Innanen and Seppo Mikkola note that "contrary to intuition, there is clear empirical evidence for the stability of motion around the L4 and L5 points of all the terrestrial planets over a timeframe of several million years".
Since the discovery of 5261 Eureka, other Mars Trojans have been identified; namely 1999 UJ7 at the L4 point and 1998 VF31, 2001 DH47, 2001 FG24, and 2001 FR127 at the L5 point. The co-orbitals 1998 QH56 and 1998 SD4 will not remain as Trojans —they will be perturbed away by Mars within the next 500,000 years or so.
Note, however, that as of 2005 the Minor Planet Center does not officially recognize any asteroid as being a Mars Trojan [1]: "in light of some recent ill-informed speculations on an astronomy-related Yahoo group of which the MPC has been made aware, this [Martian Trojan] list is being removed for the foreseeable future."
The infrared spectrum for 5261 Eureka is typical of an A-class asteroid, but the visual spectrum is consistent with an evolved form of achondrite called an angrite. A-class asteroids are tinted red in hue, with a moderate albedo. 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 the solar system.
[edit] References
- IAUC 5045
- IAUC 5047
- IAUC 5067
- IAUC 5075
- A. S. Rivkin, R. P. Binzel, S. J. Bus, and J. A. Grier, Spectroscopy and Classification of Mars Trojan Asteroids, 2002, Bulletin of the American Astronomical Society, 34, #3.
- S. Tabachnik and N. W. Evans, Cartography for Martian Trojans, April 1999.
| Minor planets | ||
|---|---|---|
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| List of asteroids | ||
Vulcanoids · Near-Earth asteroids · Main belt · Jupiter Trojans · Centaurs · Damocloids · Comets · Trans-Neptunians (Kuiper belt • Scattered disc • Oort cloud)
For other objects and regions, see Asteroid groups and families, Binary asteroids, Asteroid moons and the Solar System.
For a complete listing, see List of asteroids. See also Pronunciation of asteroid names and Meanings of asteroid names.
