On the puzzle of space weathering alteration of basaltic asteroids

TL;DR

This study investigates whether space weathering explains the spectral diversity of basaltic asteroids and HED meteorites, finding a potential reddening timescale of about 0.5 billion years but also highlighting unresolved puzzles.

Contribution

It provides the first analysis of spectral slopes of V-types and HEDs using SDSS photometry to assess space weathering effects.

Findings

V-types have systematically redder spectral slopes than HEDs.

Estimated space weathering reddening timescale is about 0.5 billion years.

Spectral mismatch poses puzzles for understanding asteroid surface processes.

Abstract

The majority of basaltic asteroids are found in the inner main belt, although a few have also been observed in the outer main belt and near-Earth space. These asteroids -referred to as V-types- have surface compositions that resemble that of the 530km sized asteroid Vesta. Besides the compositional similarity, dynamical evidence also links many V-type asteroids to Vesta. Moreover, Vesta is one of the few asteroids to have been identified as source of specific classes of meteorites, the howardite, eucrite, diogenite achondrites (HEDs). Despite the general consensus on the outlined scenario, several questions remain unresolved. In particular, it is not clear if the observed spectral diversity among Vesta, V-types and HEDs is due to space weathering, as is thought to be the case for S-type asteroids. In this paper, SDSS photometry is used to address the question of whether the spectral diversity among candidate V-types and HEDs can be explained by space weathering. We show that visible spectral slopes of V-types are systematically redder with respect to HEDs, in a similar way to what is found for ordinary chondrite meteorites and S-types. On the assumption that space weathering is responsible for the slope mismatch, we estimated an upper limit for the reddening timescale of about 0.5Ga. Nevertheless, the observed slope mismatch between HEDs and V-types poses several puzzles to understanding its origin. The implication of our findings is also discussed in the light of Dawn mission to Vesta.