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Surprising Thermophysical Properties of CM Carbonaceous Chondrites

Presentation #402.04 in the session “Asteroids: Bennu and Ryugu 1”.

Published onOct 26, 2020
Surprising Thermophysical Properties of CM Carbonaceous Chondrites

Measurements of the low-temperature thermodynamic and physical properties of meteorites provide fundamental data for understanding asteroids and other small bodies. CM carbonaceous chondrites represent a class of primitive meteorites that record substantial chemical information concerning the evolution of volatile-rich materials in the early solar system. We have measured the thermal conductivity, heat capacity and thermal expansion of six CM2 carbonaceous chondrites (Murchison, Murray, Cold Bokkeveld, Northwest Africa 7309, Jbilet Winselwan, and Aguas Zarcas) at low temperatures (5-300 K), which span the range of possible surface temperatures in the asteroid belt and outer solar system. 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. However, the specimens exhibit an unexpected substantial negative thermal expansion (NTE) over the range 210–240 K followed by pronounced positive expansion over 240–300 K. This transition has not been seen in anhydrous CV or CO carbonaceous chondrites. The broad NTE behavior in CMs centered at ~ 235 K produced by serpentine-group phyllosilicates is likely an important factor in the evolution of serpentine-rich mineralogy asteroids in response to the physical environment of the inner solar system. We conclude that serpentine-rich near earth object (NEO) parent bodies are likely to be subjected to stronger physical weathering, degradation of surface strength properties, and increased dust production. This increased relative stress in the inner solar system may also lead to a more rapid breakup of phyllosilicate rich asteroid parent bodies in the NEO population.

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