Combined SEM (secondary electrons, backscatter, cathodoluminescence) and atomic force microscope investigation of fracture surfaces in Martian meteorite ALH84001: Preliminary results

A variety of microscope techniques has been used to study surficial phenomena on the fracture surfaces of the Martian meteorite ALH84001. The aim of the investigation was to determine the most useful microscopic methods in the search for morphological signs of biogenic activity. Emphasis was placed on scanning electron microscopy (SEM) using secondary, backscatter and cathodoluminescence modes combined with observation of samples at a variety of accelerating voltages (1- 20 KV). High resolution SEM imaging was compared with atomic force microscopy (APM). These techniques revealed a number of structures of possible abiotic and biotic origin: (1) a large (150× 50 μm), fibrous-looking carbonaceous structure, (2) fine, flaky films (tens of nanometers thick) coating pyroxene surfaces, (3) finely granular calcium carbonate deposits associated with the fine film, and (4) lacy-structured, mineralised polymers on the pyroxene surface. Another sample contains further evidence of water-lain deposits in a cracked, iron oxide coat on a fracture surface.