21 Lutetia
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Discovery
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| Discovered by | Hermann M. S. Goldschmidt |
| Discovery date | November 15, 1852 |
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Designations
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| Alternative names | none |
| Minor planet category |
Main belt |
| Epoch January 30, 2005 (JD 2453400.5) | |
| Aphelion | 423.955 Gm (2.834 AU) |
| Perihelion | 304.600 Gm (2.036 AU) |
| Semi-major axis | 364.277 Gm (2.435 AU) |
| Eccentricity | 0.164 |
| Orbital period | 1387.902 d (3.80 a) |
| Average orbital speed | 18.96 km/s |
| Mean anomaly | 75.393° |
| Inclination | 3.064° |
| Longitude of ascending node | 80.917° |
| Argument of perihelion | 250.227° |
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Physical characteristics
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| Dimensions | 120×100×80 km [1][2][3] |
| Mass | ~1.3×1018 |
| Mean density | ~2.7 g/cm³ [4] |
| Equatorial surface gravity | ~0.025 m/s² |
| Escape velocity | ~0.05 km/s |
| Rotation period | 0.3402 d (8.165 h) [5] |
| Albedo | 0.208 [3] |
| Temperature | ~172 K max: 266 K (-7 °C) |
| Spectral type | M [5] |
| Apparent magnitude | 9.24 (brightest) |
| Absolute magnitude | 7.29 [6] |
21 Lutetia (pronounced /ljuˈtiːʃiə/, Latin: Lutētia) is a large Main belt asteroid of the M spectral type, about 100 kilometers in diameter. It will be the subject of a flyby by the Rosetta space probe in 2010.
The name Lutetia derives from the Latin name for Paris.
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[edit] Characteristics
The composition of Lutetia has puzzled astronomers for some time, and its investigation has picked up in recent years in anticipation of the upcoming Rosetta flyby. While classified as the M spectral type, it is one of the anomalous members which do not display much evidence of metal on their surface. In fact, there are various indications of a non-metallic surface: A flat low frequency spectrum similar to that of carbonaceous chondrites and C-type asteroids [7] and not at all like that of metallic meteorites, a low radar albedo whereas strongly metallic asteroids like e.g. 16 Psyche have a high one [6], evidence of hydrated materials on its surface [8], abundant silicates [9] and a thicker regolith than most asteroids [10].
Lightcurve analysis indicates that Lutetia's pole points towards either ecliptic coordinates (β, λ) = (3°, 40°) or (β, λ) = (3°, 220°) with a 10° uncertainty [2]. This gives an axial tilt of 85°, or 89°, respectively, meaning that Lutetia spins at an approximately right angle to the ecliptic like e.g. Uranus.
[edit] Exploration
Lutetia was discovered on November 15, 1852 by Hermann Mayer Salomon Goldschmidt from the balcony of his apartment in Paris.
On July 10, 2010, the European Rosetta comet probe will pass the asteroid with a minimum distance of 3000 km and a velocity of 15 kilometres per second on its way to 67P/Churyumov-Gerasimenko.[11] In the run-up to this event the attention of astronomers has been drawn to Lutetia.
The flyby will be important for the understanding of the asteroids, since Lutetia will be the first M-type asteroid to be visited by a spacecraft.
There have been two reported stellar occultations by Lutetia: from Malta (1997) and Australia (2003), with only one chord each, roughly agreeing with IRAS measurements.
[edit] References
- ^ Supplemental IRAS Minor Planet Survey
- ^ a b J. Torppa et al. (2003). "Shapes and rotational properties of thirty asteroids from photometric data". Icarus 164: 346.
- ^ a b M. Mueller et al. (2006). "The size and albedo of Rosetta fly-by target 21 Lutetia from new IRTF measurements and thermal modeling". Astronomy & Astrophysics 447: 1153.
- ^ G. A. Krasinsky et al. (2002). "Hidden Mass in the Asteroid Belt". Icarus 158: 98.
- ^ a b PDS lightcurve data
- ^ a b C. Magri et al. (1999). "Mainbelt Asteroids: Results of Arecibo and Goldstone Radar Observations of 37 Objects during 1980-1995". Icarus 140: 379.
- ^ Birlan, M., et al. (2004). "Near-IR spectroscopy of asteroids 21 Lutetia, 89 Julia, 140 Siwa, 2181 Fogelin and 5480 (1989YK8) [sic], potential targets for the Rosetta mission; remote observations campaign on IRTF". New Astronomy 9: 343.
- ^ M. Lazzarin et al. (2004). "Visible spectral properties of asteroid 21 Lutetia, target of Rosetta Mission". Astronomy and Astrophysics 425: L25.
- ^ M. A. Feierberg et al. (1983). "Detection of silicate emission features in the 8- to 13 micrometre spectra of main belt asteroids". Icarus 56: 393.
- ^ A. Dollfus & J. E. Geake (1975). "Polarimetric properties of the lunar surface and its interpretation. VII - Other solar system objects". Proceedings of the 6th Lunar Science Conference, Houston, Texas, March 17-21 3: 2749.
- ^ M. A. Barucci, M. Fulchignoni and A. Rossi (2007). "Rosetta Asteroid Targets: 2867 Steins and 21 Lutetia". Space Science Reviews 128 (1-4): 67-78. doi:.
[edit] External links
- shape model deduced from lightcurve
- Orbital simulation from JPL (Java) / Ephemeris
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