Mineralogical consideration of possible microfossils in martian meteorite ALH84001.

Antarctic meteorite ALH84001 is a member of twelve martian meteorites that are widely believed to have originated on planet Mars based upon several lines of evidence. ALH84001 is an ancient orthopyroxenite rock of 4.5 billion years old that contains abundant Ca–Fe–Mg carbonates, unlike other martian meteorites. Recently, it has been reported that ALH84001 contains (1) unique mineral compositions and biominerals, (2) polycyclic aromatic hydrocarbons (PAHs) in association with carbonates, and (3) unique structures and morphologies typical of nannobacteria or microfossils. They are interpreted as a possible relic biogenic activity on early Mars. We review the possibility of alternative explanations for these phenomena, especially for mineralogical features in the carbonate globules. Although it may be possible to consider that such phenomena in carbonates are biogenic rather than inorganic in origin, we show more difficulty in the biogenic interpretation than has been discussed. Because it is very difficult to conclude that they are biogenic or non-bio-genic from present data, it is necessary to further study ALH84001 and other martian meteorites. We also need to consider future Mars missions, especially sample return missions. In this consequence, we should start to think about a curation system and analytical facilities in Japan in cooperation with other related communities.