OPP 9615276 Harvey Abstract This award supports continuation of the Antarctic Search for Meteorites (ANSMET) for the 97/98, 98/99, and 99/2000 austral summer field seasons in Antarctica. Since 1976, ANSMET has recovered more than 7800 meteorite specimens from locations along the Transantarctic Mountains. Over the next three years, systematic searches will be conducted in regions known to contain meteorites and reconnaissance work will be conducted to discover new concentrations. During the 1997-98 field season work will be done in the Pecora Escarpment-LaPaz Icefields region, where several small ice fields remain unsearched and earlier reconnaissance located significant concentrations. During the 1998-99 field season the southern Walcott N?v? region will be visited, where more than 1500 meteorites have already been recovered and many more remain. During the 1999-00 field season several ice fields in the Dominion Range- Grosvenor Mountains- Scott Glacier region will be visited, where previous reconnaissance and incomplete systematic searching promise significant meteorite recoveries. Antarctica is the world's premier meteorite hunting-ground for two reasons. Although meteorites fall in a random fashion all over the globe, the likelihood of finding a meteorite is enhanced if the background material is plain and the accumulation rate of terrestrial sediment is low. Consequently the East Antarctic Ice Sheet, provides an ideal background for meteorite recovery. This allows the recovery of meteorites without bias toward types that look most different from earth rocks (a problem on the other continents) and without bias toward larger sizes. But another factor may be equally important. As the East Antarctic Ice Sheet flows toward the margins of the continent, it's progress is occasionally blocked by mountains or obstructions below the surface of the ice. In these areas, old deep ice is pushed to the surface and can become stagnant, with very little outf low and consistent, slow inflow. When such places are exposed to strong katabatic winds, massive deflation results, removing large volumes of ice and preventing accumulation of snow while leaving a lag deposit of meteorites on the surface. These areas exhibit a balance between inflow, outflow and deflation, all of which are intimately tied to environmental change during recent Antarctic history. Over significant stretches of time large concentrations of meteorites can develop, as high as 1 per square meter. Terrestrial exposure ages of meteorites suggest that some of these ice surfaces are very old. Antarctica is by far the best place on Earth to search for meteorites, and the ANSMET program has proven to be reliable and cost effective. Continued recovery of Antarctic meteorites is important for several reasons. These samples have been the only reliable source of new, non-microscopic extraterrestrial material since the Apollo project, and will continue to be until future planetary sample-return missions develop (none are currently scheduled for launch). These samples provide essential "ground- truth" about the composition of asteroids, planets and other bodies of our solar system. Studies of these materials have fundamentally changed our understanding of the solar system, greatly extending our knowledge of the materials and conditions present in the nebula from which our solar system was born 4.556 billion years ago. ANSMET meteorites provide samples of asteroids ranging from primitive bodies unchanged since the formation of the solar system to complex, miniature planets, where both traditional and exotic geological activity has taken place. Other ANSMET samples proved, against the conventional wisdom, that some meteorites actually represent planetary materials, delivered to us from the Moon and Mars. ANSMET meteorites have even promoted the discovery that meteorites can be used to do astronomy, through the study of isotopically anomalous grains that could only have evolved in a different stellar environment.
