Marsha A. Presley

Abstract: A line-heat source apparatus was assembled for the purpose of measuring thermal conductivities of particulate samples under low pressures of a carbon dioxide atmosphere. The primary result of this project is the compilation of the first comprehensive suite of measurements of the dependence of thermal conductivity on particle size. The thermal conductivity increases with increasing particle size and atmospheric pressure. In particular, over the range of Martian atmospheric pressures, from 1 to 7 torr, the thermal conductivity was found to be empirically related to approximately the square root of the particle diameter and the square of the cubed root of the atmospheric pressure. At the average pressure of the Martian surface (6 torr) the thermal conductivity varies from 0.011 W/m K, for particles less than 11 μm in diameter, to 0.11 W/m K, for particles 900 μm in diameter. These results differ significantly from the particle size dependence estimated for Mars from previous measurements, except for 200-μm particles, whose thermal conductivity is 0.053 W/m K. The thermal conductivities of larger particles are lower than the previous estimate, by 40% at 900 μm, and the thermal conductivities of smaller particles are higher than the previous estimate, by 60% at 11 μm. These newer estimates agree with other lines of evidence from Martian atmospheric and surficial processes and lead to improved particle size estimates for most of the planet's surface.

TL;DR: A review of the methodology available for the study of thermal conductivity of particulate materials, with an emphasis on low atmospheric pressures, and an assessment of the dependability of the data previously reported is presented in this article.

TL;DR: In this article, the effects of bulk density and particle size sorting on the thermal conductivity of particulate materials under Martian atmospheric pressures are discussed and preliminary measurements of the results are presented and discussed.

TL;DR: The Mars Microprobe Mission (MPM) as mentioned in this paper is the second of the New Millennium Program's technology development missions to planetary bodies and consists of two identical penetrators that will impact the surface at ∼190 m/s and penetrate up to 0.6 m. They will land within 1 to 10 km of each other and ∼50 km from the Polar Lander on the south polar layered terrain.

TL;DR: In this article, a line-heat source apparatus was used to measure thermal conductivities of natural fluvial and eolian particulate sediments under low pressures of a carbon dioxide atmosphere.