Collisions, Cosmic Radiation and the Colors of the Trojan Asteroids

TL;DR

This paper investigates the surface composition and coloration of Trojan asteroids, suggesting they are mainly covered with unirradiated dust due to resurfacing processes and cosmic radiation effects.

Contribution

It proposes a model linking resurfacing timescales with dust irradiation, explaining the observed colors and volatile loss in Trojan asteroids.

Findings

Trojan asteroid surfaces are mainly unirradiated dust.

Resurfacing timescales match dust color flattening due to solar-proton irradiation.

Surface composition is consistent with dust layers affected by cosmic radiation.

Abstract

The Trojan asteroids orbit about the Lagrangian points of Jupiter and the residence times about their present location are very long for most of them. If these bodies originated in the outer Solar System, they should be mainly composed of water ice, but, in contrast with comets, all the volatiles close to the surface would have been lost long ago. Irrespective of the rotation period, and hence the surface temperature and ice sublimation rate, a dust layer exists always on the surface. We show that the timescale for resurfacing the entire surface of the Trojan asteroids is similar to that of the flattening of the red spectrum of the new dust by solar-proton irradiation. This, if the cut-off radius of the size distribution of the impacting objects is between 1mm and 1m and its slope is -3, for the entire size-range. Therefore, the surfaces of most Trojan asteroids should be composed mainly of unirradiated dust.