Space weathering of near-Earth and main belt silicate-rich asteroids: observations and ion irradiation experiments

¹ Dipartimento di Astronomia, Vicolo dell'Osservatorio 2, 35122 Padova, Italy e-mail: [marchi;s.magrin;lazzarin]@pd.astro.it
² Dipartimento di Fisica, Università di Lecce, via Arnesano, 73100 Lecce, Italy e-mail: rbrunetto@ct.astro.it
³ INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
⁴ Dipartimento di Fisica e Astronomia, Università di Catania, via S. Sofia 78, 95123 Catania, Italy e-mail: dgandolfi@ct.astro.it


Received: 26 May 2005
Accepted: 29 July 2005

Abstract

In this paper we report the results of a comparison between ion irradiation experiments (N⁺, Ar⁺, Ar⁺⁺) on silicates, a large spectral data set of silicate-rich (S-type) asteroids, and ordinary chondrite meteorites (OCs). Ion irradiation experiments – conducted on Fe-poor olivine, Fe-poor orthopyroxene, bulk silicate-rich rocks and one OC – have been monitored by means of reflectance spectroscopy (0.3–2.5 μm). All these experiments produce reddening and darkening of reflectance spectra. The observational data consist of a set of visible and near-infrared (0.4–2.4 μm) spectra of S-type asteroids, that belong to main belt (MBAs) and near-Earth (NEOs) populations. By analyzing the spectra of OCs, MBAs, and NEOs, we find a similar mineralogy between most asteroids and meteorites, but different distributions of spectral slopes. We interpret these findings in the frame of space weathering induced by solar wind ion irradiation.