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Science Frontiers ONLINE No. 101: Sep-Oct 1995 |
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Alh 84001: a message from mars or perhaps some other planet
ALH 84001 is a meteorite picked up in the Allan Hills of Antarctica a decade ago. Its composition and fused crust suggest an extraterrestrial -- origin probably Mars. Space scientists think ALH 84001 was blasted off the Martian surface by an impacting body 14-18 million years ago, based upon its exposure to cosmic rays while circling the sun, edging ever closer to earth.
The composition of ALH 84001 tells us curious facts about its place of origin. First, it contains carbonate minerals deposited by water. Second, the carbonate grains are banded, implying the parent rock formation was washed by water more than once. Third, and most interesting, chemists have found traces of molecules called PAHs, based on interconnected benzene rings. Three sources have been proposed for these PAHs:
- Terrestrial contamination
- Prebiotic activity on the planet of origin
- PAH-bearing comets and/or asteroids impacting the parent planet.
Terrestrial contamination has always been a problem in analyzing meteorites, but great care has been taken in recent years, especially with the Antarctic lode of meteorites. In view of these precautions, it seems rather likely that somewhere "out there" life is brewing. (Anonymous; "A Chip Off the Old Mars," Sky and Telescope, 90:12, July 1995.)
Reference: See also: Incredible Life for the interesting history of past "discoveries of life in meteorites. This book is described here.