21 Lutetia (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.
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
, 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, evidence of hydrated materials on its surface, abundant silicates, and a thicker regolith
than most asteroids.
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. 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.
Lutetia was discovered on November 15
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. 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.