Annama H chondrite - mineralogy, physical properties, cosmic ray exposure, and parent body history

TL;DR

The Annama meteorite, a typical H chondrite with a high Ar-Ar age, exhibits an unusual cosmic ray exposure history suggesting it was part of a larger parent body and recently broke up, providing insights into its origin and evolution.

Contribution

This study provides detailed mineralogical, physical, and cosmic ray exposure data for Annama, revealing its atypical exposure age and recent breakup, advancing understanding of H chondrite parent body history.

Findings

Annama is a typical H chondrite with a 4.4 Ga Ar-Ar age.

Its cosmic ray exposure age peaks at 30 ± 4 Ma, not the common 7-8 Ma peak.

Recent breakup 3-5 Ma ago reduced its size to 30-35 cm.

Abstract

The fall of the Annama meteorite occurred early morning (local time) on April 19, 2014 on the Kola Peninsula (Russia). Based on mineralogy and physical properties, Annama is a typical H chondrite. It has a high Ar-Ar age of 4.4 Ga. Its cosmic ray exposure history is atypical as it is not part of the large group of H chondrites with a prominent 7 - 8 Ma peak in the exposure age histograms. Instead, its exposure age is within uncertainty of a smaller peak at 30 \pm 4 Ma. The results from short-lived radionuclides are compatible with an atmosperic pre-entry radius of 30 - 40 cm. However, based on noble gas and cosmogenic radionuclide data, Annama must have been part of a larger body (radius >65 cm) for a large part of its cosmic ray exposure history. The 10Be concentration indicates a recent (3 - 5 Ma) breakup which may be responsible for the Annama parent body size reduction to 30 - 35 cm pre-entry radius.