THERMOPHYSICAL PROPERTIES OF LUNAR IRREGULAR MARE PATCHES

Irregular mare patches (IMPs) are small lunar volcanic features that appear geologically young compared with surrounding ancient mare basalts. Some properties of the IMPs (e.g., preservation of topographic relief and surface texture, low number of impact craters) suggest that they are the result of recent volcanism (within the past 100 Myr), which is inconsistent with existing thermal evolution models that predict that lunar volcanism halted more than 1 Gyr ago. Other studies have proposed that they formed contemporaneously with the surrounding maria in which they reside, and appear young due to their unique physical properties (i.e., high porosity) resulting from their eruption dynamics (i.e., volatile-rich magmatic foam). In this work, we investigate the thermophysical properties of eight of the largest lunar IMPs (Ina, Sosigenes, Cauchy-5, Maskelyne, Nubium, Ross-E-1, Maclear-2, and Arago-5) using data from the Diviner Lunar Radiometer Experiment on the Lunar Reconnaissance Orbiter. We find that, in general, the IMPs have lower thermal inertia than nearby locations in the maria. Additionally, the large IMP Ina has notably lower thermal inertia than the other IMPs, displaying values similar to those observed at lunar pyroclastic deposits. It is unclear why Ina stands out from the other IMPs; however, it may result from observational limitations due to the small sizes of many of the IMPs. The low thermal inertia at the IMPs suggests fine-grained material that is less consolidated or contains fewer small rocks than typical regolith. This could be consistent with a number of proposed formation mechanisms, including the magmatic foam, pyroclastic, and episodic outgassing hypotheses.