Allan Hills 84001

 
 

Sample Collection


ALH84001 was found by geologist Bobbie Score during a snowmobile ride on December 27th, 1984 in the Far Western Icefield of Allan Hills. It was recognized as a most unusual rock, and was the first Antarctic meteorite to be processed from the 1984-5 field season. Field notes describe it as a highly shocked greyish-green achondrite with a 90% fusion crust. Where the fusion crust had spalled away the interior showed a uniform coarse-grained rock with a blocky texture. Preliminary laboratory investigations revealed the sample had a “shocked appearance” and patches of brown iron-rich carbonate were noted. At this time the sample was classified as a diogenite. It was only six years later that its true identity would be recognized, when electron microprobe analysis established it was a SNC meteorite and hence potentially of Martian origin (SNC is an acronym for three meteorites believed to have originated on Mars - Shergotty, Nakhla and Chassigny). Further evidence of a martian origin for ALH84001 comes from the chemical composition of gases inside black beads of glass-like material (maskelynite) that had bubbled up when the rock was ejected from Mars by a violent shock. The gases matched the Martian atmosphere perfectly as measured by the Viking space craft which sampled the atmosphere in 1976.


Section Headings: Sample Collection, Mineralogy, Isotope Characteristics, Life on Mars?, Timeline, Explore ALH84001

 

Outer surface of 84001 showing brown fusion crust and green interior (width 17.5 cm, weight 1.9 kg)

Cut surface of 84001 (cube is 1 cm across)

Allan Hills 84001 has become an iconic sample for the virtual microscope team. It was one of the first extra-terrestrial samples we worked on and is arguably one of the rarest, being one of only a few Martian meteorites. The story of 84001 follows on the next few pages and is based on descriptions compiled by Rhawn Joseph, and Charles Meyer of NASA


The sample received international recognition when, in 1996, a team of scientists from NASA reported evidence for ancient bacterial life on Mars - using ALH84001.

all photographs courtesy of NASA

Allan Hills

Antarctica