Spectral studies of asteroids 21 lutetia and 4 vesta as objects of space missions |
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Authors: | V V Busarev |
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Institution: | 1.Sternberg Astronomical Institute,Moscow,Russia |
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Abstract: | 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 different and even contradictory. In spite of the
intense and versatile ground-based 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 high-temperature
mineralogy, which agrees with their albedo estimated from the Infrared Astronomical Satellite (IRAS) observations. However,
according to the opinion of some researchers, Lutetia is of the C type, and, therefore, its mineralogy is of the lowtemperature
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 delivered 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 primitive-type asteroids. When interpreting the reflectance spectra of Lutetia and Vesta, we discuss
the spectral classification by Tholen (1984) from the standpoint of its general importance for the estimation of the mineralogical
type of the asteroids and the study of their origin and evolution. |
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