Mathematics – Logic
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusm.p11a..05h&link_type=abstract
American Geophysical Union, Spring Meeting 2004, abstract #P11A-05
Mathematics
Logic
5102 Acoustic Properties, 6022 Impact Phenomena, 6205 Asteroids And Meteoroids
Scientific paper
Elastic properties of asteroids govern much of their response to impact events, and are germane to impact mitigation and exploitation strategies. However, elastic wave velocities have been one of the least explored physical quantities of meteorites. Velocities measured to date (roughly 30 determinations) show a wide range for both compression and shear wave velocities and a strong dependence upon porosity. We have measured compressional and shear wave velocities in 72 meteorites. Meteorites were measured in the form of slabs as commonly found in collections. Pieces with two roughly parallel flat sides are required to accommodate the velocity transducers' shape. Each measurement was made three times at different positions to improve statistics and to test for sample variation. Bulk densities were measured with a modified Archimedean method using ~1 mm-diameter glass beads. Porosities were measured for 9 specimens in a commercial He pycnometer. Porosities for other meteorites measured were taken from literature sources. Bulk and grain densities and porosities were generally found to be consistent with previous work, although rare large discrepancies were found. Seismic velocities were also found to be generally similar to previously obtained values. Various relationships have been quantified; velocity vs. fall date, class, petrologic type, porosity, bulk density, and darkness. Derived relationships were generally restricted to only the data obtained for ordinary chondrites, as they constituted the largest sampled population (and presumably represent the bulk of the undifferentiated asteroids). Falls from the last 50 years exhibit a smaller range of velocities indicating that older samples have experienced variable subtle weathering effects (probably crack propagation vs. filling pores by secondary minerals) from exposure to the Earth's atmosphere. This indicates that meteorite physical property studies as proxies for asteroidal properties must be restricted to the freshest possible material, and that recently fallen meteorites must be curated in inert atmospheres. Velocities inversely correlate to porosities as found in previous work, but were also found to correlate (inversely) to petrologic type in contrast to previous work. Possible darkening due to weathering complicates interpreting the observed correlation between velocity and the darkness of a meteorite (presumed to be related to shock history).
Hildebrand Alan Russell
Hons M. S.
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