GEOPHYSICS - Putting Meteorites on Ice

Every year, scientists put on their mittens and collect meteorites in Antarctica. Of the roughly 37,000 meteorites listed as of 2002, about 30,000 come from Antarctica or, to be precise, the ice sheets covering that continent. Antarctica is the best place to collect meteorites because they accumulate on blue ice fields, upstream of topographic barriers. Meteorites fall and become buried in the ice; the ice flows; the ice slows and is lifted up near a barrier; finally, wind ablation exhumes and concentrates the meteorites. Corti et al. explain how meteorites may also become trapped downstream of a barrier--specifically, Frontier Mountain, an 8-km-long granitic ridge in Northern Victoria Land. Geodetic data and laboratory simulations (using polydimethylsiloxane in
place of ice) show that the ice flow slows down and converges behind the mountain. Although katabatic winds do ablate the ice and expose the meteorites, the influence of the barrier on ice flow is crucial for corraling them in one place. Behind Frontier Mountain, the residence time of trapped meteorites would be as long as 60,000 years if there were no scientists (about 600 meteorites have been collected there in 12 years), and it is possible that downstream ice traps may be more effective than upstream ones in storing meteorites for long periods. -- Published like Editor's Choice, edited by Gilbert Chin - on SCIENCE VOL 302 31 OCTOBER 2003.