The surprising thermal properties of CM carbonaceous chondrites

1C. P. Opeil,2,3D. T. Britt,4R. J. Macke,4G. J. Consolmagno
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13556]
1Department of Physics, Boston College, 140 Commonwealth Ave., Chestnut Hill, Massachusetts, 02467 USA
2Department of Physics, University of Central Florida, 4111 Libra Dr., Orlando, Florida, 32816 USA
3The Center of Lunar and Asteroid Surface Science, 12354 Research Pkwy Suite 214, Orlando, Florida, 32826 USA
4Vatican Observatory, V‐00120 Vatican City State
Published by arrangement with John Wiley & Sons

Measurements of the low‐temperature thermodynamic and physical properties of meteorites provide fundamental data for the study and understanding of asteroids and other small bodies. Of particular interest are the CM carbonaceous chondrites, which represent a class of primitive meteorites that record substantial chemical information concerning the evolution of volatile‐rich materials in the early solar system. Most CM chondrites are petrographic type 2 and contain anhydrous minerals such as olivine and pyroxene, along with abundant hydrous phyllosilicates contained in the meteorite matrix interspersed between the chondrules. Using a Quantum Design Physical Property Measurement System, we have measured the thermal conductivity, heat capacity, and thermal expansion of five CM2 carbonaceous chondrites (Murchison, Murray, Cold Bokkeveld, Northwest Africa 7309, Jbilet Winselwan) at low temperatures (5–300 K) which span the range of possible surface temperatures in the asteroid belt and outer solar system. The thermal expansion measurements show a substantial and unexpected decrease in CM2 volume as temperature increases from 210 to 240 K followed by a rapid increase in CM2 volume as temperature rises from 240 to 300 K. This transition has not been seen in anhydrous CV or CO carbonaceous chondrites. Thermal diffusivity and thermal inertia as a function of temperature are calculated from measurements of density, thermal conductivity, and heat capacity. Our thermal diffusivity results compare well with previous estimates for similar meteorites, where conductivity was derived from diffusivity measurements and modeled heat capacities; our new values are of higher precision and cover a wider range of temperatures.

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