date: 2012 October 3 (Wed) 15:00-
room: CPS Conference Room
speaker: Natsuko Okamura (The University of Tokyo)
organizer: Ayako Suzuki
title: Widespread distribution of hydrous minerals on dark asteroids in the main belt discovered by AKARI
abstract: The distribution of hydrous minerals on asteroidal surfaces in the main asteroid belt is expected to hold key information for understanding the formation and early evolution of the Solar System (e.g., Lecar et al., 2006). Although hydrous minerals can be best detected through absorption bands around 2.5-2.8 μm, observation using ground-based telescopes in the former wavelength region cannot be easily performed due to telluric water. The asteroid, which has been obtained the spectra in the wavelength range including 2.5-2.8 μm, is only the dwarf planet 1 Ceres with ISO (Rivkin et al., 2002). Thus, no systematic survey on the form and distribution of hydrous minerals on asteroids has been made.
Here we show the distribution of hydrous minerals on 33 dark (albedo < 0.1) asteroids based on asteroid spectral data taken by the Japanese infrared satellite AKARI. The peak region of the hydrous minerals absorption around 2.7 μm has been clearly observed in asteroid spectra for the first time. Among our observed asteroids, hydrous minerals are present on 32. These asteroids are large (70-500 km in diameter) and are located over a wide range of semi-major axis (2.2-4 AU). In addition, we discuss new constraints on important issues, such as aqueous alterations processes during the early evolution of the Solar System.
keywords: AKARI, hydrous minerals, reflectance spectra, aqueous alterations, asteroids