Spectral investigations of asteroids 21 Lutetia and 4 Vesta as objects of space missionsстатья
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Аннотация:Asteroid 21 Lutetia is one of the objects of the Rosetta mission carried out by the European Space
Agency (ESA). The Rosetta spacecraft launched in 2004 is to approach Lutetia in July 2010, and then it will
be directed to the comet Churyumov–Gerasimenko. Asteroid 4 Vesta is planned to be investigated in 2011
from the Dawn spacecraft launched by the National Aeronautics and Space Administration (NASA) in 2007
(its second object is the largest asteroid, 1 Ceres). The observed characteristics of Lutetia and Vesta are differ
ent and even contradictory. In spite of the intense and versatile groundbased studies, the origin and evolution
of these minor planets remain obscure or not completely clear. The types of Lutetia and Vesta (M and V,
respectively) determined from their spectra correspond to the hightemperature mineralogy, which agrees
with their albedo estimated from the Infrared Astronomical Satellite (IRAS) observations. However, accord
ing to the opinion of some researchers, Lutetia is of the C type, and, therefore, its mineralogy is of the low
temperature type. In turn, hydrosilicate formations have been found in some places on the surface of Vesta.
Our observations also testify that at some relative phases of rotation (RP), the reflectance spectra of Lutetia
and Vesta demonstrate features confirming the presence of hydrosilicates in the surface material. However,
this fact can be reconciled with the magmatic nature of Lutetia and Vesta if the hydrated material was deliv
ered to their surfaces by falling primitive bodies. Such small bodies are probably present everywhere in the
main asteroid belt and can be the relicts of silicate–icy planetesimals from Jupiter’s formation zone or the
fragments of primitivetype asteroids. When interpreting the reflectance spectra of Lutetia and Vesta, we dis
cuss the spectral classification by Tholen (1984) from the standpoint of its general importance for the estima
tion of the mineralogical type of the asteroids and the study of their origin and evolution.