A Global Thermal Conductivity Model for Lunar Regolith at Low Temperatures

Although some of the coldest surface temperatures in the entire Solar System are found near the poles of our own Moon, the thermophysical properties of lunar regolith at these ultracold temperatures (i.e., below similar to 150 K) are not well understood. Standard lunar thermal models generally match the surface temperatures observed by global orbital remote sensing data but are inconsistent with infrared data collected from ultracold polar terrain. We build upon previous theoretical work on the low-temperature physics of lunar regolith to introduce a global thermal conductivity model consistent with the temperature trends observed by the Diviner Lunar Radiometer Experiment (Diviner). This updated thermophysical model primarily affects nighttime surface temperatures, subsurface temperatures at high latitudes, and permanently shadowed regions (PSRs). An additional outcome of this thermophysical model is the ability to accommodate the surface temperature trends observed by Diviner both in warm low latitudes and cold high latitudes. Subsurface temperatures in near-polar craters are similar to 5-10 K warmer than previous thermal models, and cooler nighttime surface temperatures are observed globally. Model results of PSRs reveal larger surface temperature amplitudes (as observed by Diviner) and steeper geothermal gradients. A comprehensive understanding of lunar regolith's low-temperature thermal behavior is an essential step in modeling the potential location and quantity of cold trapped volatiles in the lunar south pole. Here, we hope to provide theoretical support and motivation for more complete low-temperature thermal conductivity laboratory measurements.

Automated summary

This study introduces a global thermal conductivity model that can better explain the temperature trends in polar regions of the Moon, providing more accurate theoretical support for the Diviner experiment. Additionally, the model shows higher subsurface temperatures and steeper geothermal gradients.