Hayne, Paul - Thermal Inertia of the Moon from Diviner Lunar Radiometer Measurements

Thermal inertia is a quantity that characterizes a material’s resistance to changes in temperature. In remote sensing, thermal inertia is often used to infer physical properties of planetary surfaces by observing temperature oscillations occurring on known time scales. Unconsolidated particulate materials such as the lunar regolith tend to have low thermal inertia, and consolidated materials such as boulders and bedrock tend to have high thermal inertia. Long-period temperature oscillations (such as seasonal cycles) sense greater depths than short-period oscillations (such as a lunar eclipse); this allows retrieval of depth profiles of thermal inertia. Thus, it is possible to derive information about the history and present state of a geologic unit by measuring its temperature variations on various time scales. While the Moon’s temperature has been measured for nearly a century, the Diviner Lunar Radiometer provides a dataset of unprecedented accuracy and coverage, as well as spatial and temporal resolution. We used Diviner data spanning nearly five years (60 lunar diurnal cycles) to constrain models of regolith thermal inertia, and mapped the results at a resolution of 128 pixels per degree from -70 to +70 degrees latitude. As we will show, the results clearly differentiate old and young craters by their relative thermal inertia values, and show regional and global patterns indicating the imprint of regolith formation by impacts over time. This new dataset has potential applications to a broad range of problems in lunar science, and the technique is widely applicable to airless bodies throughout the Solar System.