5261 Eureka
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| Discovery A | |
|---|---|
| Discoverer | David H. Levy |
| Discovery date | June 20, 1990 |
| Alternate designations B |
1990 MB |
| Category | Mars-crosser asteroid |
| Orbital elements C | |
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|
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| Eccentricity (e) | 0.065 |
| Semi-major axis (a) | 227.908 Gm (1.523 AU) |
| Perihelion (q) | 213.132 Gm (1.425 AU) |
| Aphelion (Q) | 242.684 Gm (1.622 AU) |
| Orbital period (P) | 686.829 d (1.88 a) |
| Mean orbital speed | 24.11 km/s |
| Inclination (i) | 20.280° |
| Longitude of the ascending node (Ω) |
245.108° |
| Argument of perihelion (ω) |
95.361° |
| Mean anomaly (M) | 104.086° |
| Physical characteristics D | |
| Dimensions | ~2-4 km |
| Mass | ? kg |
| Density | ? g/cm³ |
| Surface gravity | ? m/s² |
| Escape velocity | ? km/s |
| Rotation period | ? d |
| Spectral class | ? |
| Absolute magnitude | 16.1 |
| Albedo (geometric) | ? |
| Mean surface temperature |
~225 K |
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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| Previous minor planet | 5261 Eureka | Next minor planet |
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| 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. |
