Thermal Conductivities of Two Basaltic Achondrite Meteorites

Astronomy and Astrophysics – Astronomy

Scientific paper

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Scientific paper

In our ongoing survey of the physical properties of meteorites, we have measured the thermal conductivity for the basaltic achondrite meteorites Frankfort, a howardite likely to be typical of material on the surface of asteroid 4 Vesta, and Los Angeles, a shergottite believed to have originated on Mars, at temperatures ranging from 300K to 5K. From 300K to 100K, the conductivity of Frankfort decreases gradually from 1.6 to 1.2 W/mK; that of Los Angeles drops from 0.9 to 0.5 W/mK. At lower temperatures the thermal conductivity of both meteorites continues to drop, but more rapidly, to values below 0.1 W/mK at 10K. We find that for both meteorites the conductivity is significantly lower than would be expected from averaging the laboratory conductivities of their constituent minerals. These results are similar to results from measurements of ordinary chondrites (Opeil et al 2010, Icarus 208, 449). The monotonic decrease of conductivity with temperature over this range is different from the expected conductivity of pure minerals, which tend to vary as 1/T. This indicates that, in common with the ordinary chondrites, the conductivity we measure is controlled by the presence of shock-induced microcracks within the meteorites, which provide a barrier to the transmission of thermal energy via phonons. Thus these measurements may accurately describe the conductivity of material at the surfaces of their parent bodies. However results from surface samples may significantly underestimate the actual conductivity of material deeper in the parent bodies, depending on how characteristic the shock history of these meteorites reflects material still in place inside these bodies.

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