Nuclear track studies of the SNC meteorite ALH 84001

Details Nuclear track studies of the SNC meteorite ALH 84001 Nuclear track studies of the SNC meteorite ALH 84001

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29r.534s&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 534

Other

3

Meteoritic Composition, Oxygen Isotopes, Particle Tracks, Petrography, Shergottites, Cosmology, Ejecta, Mars (Planet), Mathematical Models, Shock Heating

Scientific paper

ALH 84001, classified initially as a diogenite, has recently been identified as a new unusual SNC meteorite based on petrographic and O isotopic composition. In fact, the unusual Xe isotopic composition of ALH 84001, with extremely high Xe-129/Xe-132, that did not match the expected signature in howardite, eucrite and diogenite (HED) meteorites, was also noted by Miura et al. In this study we have analyzed nuclear track records in several samples of ALH 84001 to determine the extent of its atmospheric ablation. Dynamical modeling suggests that martian ejecta that can give rise to SNC meteorites will enter the Earth only slightly above the Earth's escape velocity and the expected ablation loss is small (approximately 50%). This model is also consistent with the low exposure ages of the SNC meteorites. These suggestions were strengthened by the nuclear track and other cosmogenic data obtained for the shergottites. In the present work, we have studied cosmic-ray-produced nuclear track records in five samples of ALH 84001, taken from close to the fusion crust (approximately 0.5 cm away from the crust), and one sample from the interior region. Although radionuclide data rule out the possibility of a two stage exposure history for the shergottites, the same need not be true for the NC group. The possibility that ALH 84001 had a two-stage exposure history, with a significant production of cosmogenic nuclides during its exposure in martian regolith or in space before its final break-up, can be ascertained when additional data on cosmogenic stable and radionuclides become available.

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