Presentation #114.01 in the session MBAs: Physical Characteristics, Part 1.
Over the past five years we have measured the physical properties of meteorites in classes closely associated with asteroids and other solar system bodies that have been sampled or are soon to be closely studied by spacecraft missions. Following our previous measurements of density and porosity, we now have data for heat capacity and thermal conductivity, measured over the temperature range of 5 K – 300 K, from which thermal inertia and thermal diffusivity can be calculated. For many samples we have also measured the coefficient of thermal expansion as a function of temperature over this range. These temperatures are especially relevant for main belt and outer solar system objects, and deeply shadowed lunar regions.
Our results for CM meteorites (close analogs to asteroids Bennu and Ryugu) and iron meteorites (an important constituent of asteroid Psyche) are now published. Work on lunar and martian meteorites are in process. We report here on the most important results that have come from our measurements.
1. Thermal conductivity of these meteorites is strongly suppressed compared to the conductivity of pure crystals, almost certainly reflecting the heavily fractured nature of these samples.
2. Thermal properties are very strong functions of temperature in the range measured. Thermal diffusivities and inertias at asteroidal surface temperatures (circa 200 K) may be half or less of what would be measured at room temperature.
3. CM materials show a significant negative thermal expansion behavior between 200–250 K upon heating.
4. A similar negative thermal expansion, but smaller in magnitude, is found for lunar meteorites at temperatures below 50 K.
Our results have already been shown to be important for understanding the physical state of asteroidal surfaces. They have important applications in the modeling of the thermal evolution of these bodies and their observed infrared emission, and can factor into our understanding of how they respond to Yarkovsky and YORP forces.