AKARI/IRC Near-Infrared Asteroid Spectroscopic Survey: AcuA-spec

TL;DR

This survey used the AKARI satellite to detect water-related minerals on asteroids by observing their 3-micron absorption features, revealing hydration in C-complex asteroids but not in S-complex ones.

Contribution

First large-scale 3-micron spectroscopic survey of asteroids using AKARI, providing new data on asteroid hydration features and releasing the AcuA-spec catalog.

Findings

Most C-complex asteroids show hydration features at 2.75 microns.

S-complex asteroids lack significant hydration features.

Data from 66 asteroids are publicly available in the AcuA-spec catalog.

Abstract

Knowledge of water in the solar system is important for understanding of a wide range of evolutionary processes and the thermal history of the solar system. To explore the existence of water in the solar system, it is indispensable to investigate hydrated minerals and/or water ice on asteroids. These water-related materials show absorption features in the 3-$\micron$ band (wavelengths from 2.7 to 3.1 $\micron$). We conducted a spectroscopic survey of asteroids in the 3-$\micron$ band using the Infrared Camera (IRC) on board the Japanese infrared satellite AKARI. In the warm mission period of AKARI, 147 pointed observations were performed for 66 asteroids in the grism mode for wavelengths from 2.5 to 5 $\micron$. According to these observations, most C-complex asteroids have clear absorption features ($> 10\%$ with respect to the continuum) related to hydrated minerals at a peak wavelength of approximately 2.75 $\micron$, while S-complex asteroids have no significant feature in this wavelength range. The present data are released to the public as the Asteroid Catalog using AKARI Spectroscopic Observations (AcuA-spec).