The Porosity of Asteroids and Meteorites: First Results from the Vatican Collection.

Details The Porosity of Asteroids and Meteorites: First Results from the Vatican Collection. The Porosity of Asteroids and Meteorites: First Results from the Vatican Collection.

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.1044b&link_type=abstract

American Astronomical Society, DPS meeting #28, #10.44; Bulletin of the American Astronomical Society, Vol. 28, p.1106

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Spacecraft determined densities exist for Ida (2.6 +/- 0.5), Phobos (1.53 +/- 0.1), and Deimos-(1.34 +/- 0.83). These data have been used to suggest possible candidate compositions for these bodies and asteroids in general. We have begun a systematic measurement of densities and porosities of meteorites, including types never before measured, starting with 40 meteorites from the Vatican Observatory collection. Our technique utilizes a modified Archimedean method (non- contaminating 40 micron glass spheres substituting for a fluid) to determine bulk density and a custom helium pycnometer to determine grain density and thus porosity. Our early results have significantly increased the meager knowledge of meteorite density and porosity. Carbonaceous chondrites generally have porosities of 20% but their densities vary strongly with type. Orgueil (CI) has a bulk density of 1.58 +/- 0.01, significantly lower than any previously published meteorite density. Its porosity is 26% +/- 8. Other carbonaceous chondrites measured include Ornans (CO3), bulk density 2.36 +/- 0.03; Allende (CV3), bulk density 2.92 +/- 0.01, porosity 21 +/- 2%; and Vigarano, (CV3) bulk density 3.18 +/- 0.04. Porosities of ordinary chondrites rarely exceed 15%, and show a systematic decrease with weathering. There appears to be no correlation between porosity and petrographic type. Mesosiderite bulk densities range from 4 to 4.5, and pallasites cluster around 5.0, in the limited sample measured to date. If these densities are proper analogs for asteroid materials, the asteroids measured to date must have significant macro-porosity, void spaces that do not show up on meter to centimeter size scales of the meteorites. For instance, at least 15-20% additional macroporsity is required to make Ida out of H chondrite material. These studies can provide further important clues to asteroid internal structure.

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