Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001

TLDR

Fresh fracture surfaces of the Martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons and carbonate globules that resemble terrestrial bacterially induced carbonate precipitates. The study aims to determine whether biogenic processes formed the carbonate globules and associated PAHs in ALH84001. The authors used high‑resolution scanning and transmission electron microscopy to examine the textures and internal structures of selected carbonate globules, revealing fine‑grained secondary magnetite and iron sulfide phases. Contamination studies indicate the PAHs are indigenous, and the PAHs, carbonate globules, and their secondary mineral phases and textures suggest fossil remains of a past Martian biota.

Abstract

Fresh fracture surfaces of the martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons (PAHs). These fresh fracture surfaces also display carbonate globules. Contamination studies suggest that the PAHs are indigenous to the meteorite. High-resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and iron sulfides. The carbonate globules are similar in texture and size to some terrestrial bacterially induced carbonate precipitates. Although inorganic formation is possible, formation of the globules by biogenic processes could explain many of the observed features, including the PAHs. The PAHs, the carbonate globules, and their associated secondary mineral phases and textures could thus be fossil remains of a past martian biota.