Letter to the Editor

Asteroid colors: a novel tool for magnetic field detection? The case of Vesta

¹ LESIA, Observatoire de Paris, 92195 Meudon Principal Cedex, France e-mail: pierre.vernazza@obspm.fr
² Dipartimento di Fisica, Universita di Lecce, via Arnesano, 73100 Lecce, Italy
³ INAF - Osservatorio Astrofisico di Catania, via Santa Sofia 78, 95123 Catania, Italy
⁴ CEREGE CNRS Université d'Aix-Marseille 3, 13545 Aix en Provence Cedex 4, France
⁵ Space Sciences Laboratory, University of California at Berkeley, Berkeley, CA 94720-7450, USA

Received: 9 March 2006
Accepted: 30 March 2006

Abstract

Aims.Vesta's surface is surprisingly pristine. Although its basaltic surface is roughly similar to the lunar surface, which is intensely space weathered, its surface remains unaltered. It has been shown recently that solar-wind irradiation dominates asteroidal space weathering with a timescale on the order 10⁴–10⁶ years. Recent ion irradiation experiments on pyroxenes have shown significant reddening and darkening of the collected spectra with progressive irradiation. Since pyroxene is a major surface component of Vesta as determined by spectroscopy, we aimed to test whether the solar wind irradiation alters significantly the optical properties of the surface of Vesta.

Methods.Consequently, we performed an ion irradiation experiment on a eucrite meteorite, which characterizes the surface of Vesta well, in order to simulate the solar wind irradiation on this asteroid.

Results.Our result implies that, if solar wind ions do reach the surface of Vesta, its reflectance spectrum should be much redder and its albedo lower. Indeed, this implies that solar wind particles can not have reached the asteroid surface. This strongly suggests the presence of a magnetic field shielding the surface from solar wind ions. This is the first remote detection of the magnetic field of an asteroid based on its color.