Thermal diffusivity of lunar rocks under atmospheric and vacuum conditions

Abstract

Thermal diffusivity, k, of three lunar rocks (10049 and 10069; Type A, Apollo 11 and 14311; Apollo 14) and a terrestrial basalt (alkaline olivine basalt, Oki-doˆgo, Japan) was measured under one atmosphere and in vacuum conditions (10 −3 ∼ 10 −5 mmHg) in the temperature range from 85 to 850°K. The semi-empirical curve of k =A + B/T +CT 3 is fitted to the data in each condition. The porosity of rocks strongly affects the thermal diffusivity at low temperature ( T ≲ 500°K) in vacuum condition. At 150°K, thermal diffusivity of lunar rocks with porosity of 5.5% (10049) and 11% (10069) at one atmosphere is about 1.7 and 3.2 times of that in vacuum, respectively. The difference between the values at one atmosphere and those in vacuum decreases as the temperature increases. Measurements of k should be made at gas pressures at least lower than 10 −3 mmHg to estimate the value under lunar surface conditions.