Chelyabinsk meteorite explains unusual spectral properties of Baptistina Asteroid Family

TL;DR

This study links the Chelyabinsk meteorite to the Flora asteroid family, explaining the spectral properties of Baptistina Asteroid Family members through shock-induced surface alterations.

Contribution

It identifies the Chelyabinsk meteorite as a spectral analog for Baptistina family members and proposes impact melt and shock blackening as causes for their subdued spectral features.

Findings

Chelyabinsk meteorite contains LL5 chondrite and impact melt components.

Spectral match between Chelyabinsk mixture and Flora family asteroid (8) Flora.

Baptistina family members likely share a similar composition with Flora asteroids.

Abstract

We investigated the spectral and compositional properties of Chelyabinsk meteorite to identify its possible parent body in the main asteroid belt. Our analysis shows that the meteorite contains two spectrally distinct but compositionally indistinguishable components of LL5 chondrite and shock blackened/impact melt material. Our X-ray diffraction analysis confirms that the two lithologies of the Chelyabinsk meteorite are extremely similar in modal mineralogy. The meteorite is compositionally similar to LL chondrite and its most probable parent asteroid in the main belt is a member of the Flora family. Intimate mixture of LL5 chondrite and shock blackened/impact melt material from Chelyabinsk provides a spectral match with (8) Flora, the largest asteroid in the Flora family. The Baptistina family and Flora family overlap each other in dynamical space. Mineralogical analysis of (298) Baptistina and 9 small family members shows that their surface compositions are similar to LL chondrites, although their absorption bands are subdued and albedos lower when compared to typical S-type asteroids. A range of intimate mixtures of LL5 chondrite and shock blackened/impact melt material from Chelyabinsk provides spectral matches for all these BAF members. We suggest that the presence of a significant shock/impact melt component in the surface regolith of BAF members could be the cause of lower albedo and subdued absorption bands. The parent asteroid of BAF was either a member of the Flora family or had the same basic composition as the Floras (LL Chondrite). The shock pressures produced during the impact event generated enough impact melt or shock blackening to alter the spectral properties of BAF, but keep the BAF composition largely unchanged.