The Vissannapeta eucrite

Abstract

A wholly encrusted single stone that fell in Vissannapeta, Andhra Pradesh, India has been identified as a cumulate eucrite based on its primary texture and mineral composition: anorthite (An_92.4-94.6), orthopyroxene (En_49.1-51.8Fs_44.2-49.7Wo_1.2-4.0), and clinopyroxene (En_38.8-46.8Fs_14.8-33.6Wo_19.6-46.4). The stone is pyramidal in shape, and the crust shows rib-like flow features indicating that it had an oriented passage through the atmosphere towards the terminal stage of its flight. Conditions of its fall, mineralogical characteristics, and results of measurements of cosmogenic radioactivity (²⁶Al, ²²Na, and ⁵⁴Mn) and track density are described. Aluminum-26 and ²²Na in Vissannapeta are ∼ 75% of the expected values and also lower by a similar factor compared to the activities measured in Piplia Kalan, another eucrite, which fell ∼ 18 months before Vissannapeta. Because higher activity of ²²Na and ⁵⁴Mn would be expected from solar cycle modulation of galactic cosmic rays, these results, as well as the track density gradient, indicate that Vissannapeta was a small body (≤ 120 kg) in the interplanetary space wherein the nuclear cascade due to galactic cosmic rays did not develop fully. Tracks, surface morphology, and crustal features indicate at least two fragmentation events in the atmosphere.