Thermal and Illumination Environments of Lunar Pits and Caves: Models and Observations From the Diviner Lunar Radiometer Experiment

• Published in: Geophysical research letters 2022-07, Vol.49 (14), p.n/a
• Main Authors: Horvath, Tyler, Hayne, Paul O., Paige, David A.
• Format: Article
• Language: English
• Subjects: Astronauts; Black body radiation; Blackbody; Caves; Computer applications; diviner; Equator; Lunar maria; Lunar spacecraft; Lunar surface; Moon; Night; Pits; Radiative equilibrium; Radiometers; Regolith; remote sensing; space exploration; Spacecraft; Temperature; Temperature variations; Thermal emission; Thermal environments; thermal modeling; Thermophysical models; Thermophysical properties; Tubes
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL099710

Lunar collapse pits may provide access to subsurface lava tubes of unknown extent. We present Diviner Lunar Radiometer measurements showing that the Mare Tranquillitatis and Mare Ingenii pits exhibit elevated thermal emission during the night, ∼100 K warmer than the surrounding surface. Using these data, along with computational thermophysical models, we characterize the thermal environment inside pits and potential caves. Near the equator, peak day‐time temperatures on regolith‐covered pit floors can potentially reach >420 K, whereas temperatures beyond the opening in permanent shadow would maintain a nearly constant temperature of ∼290 K, similar to that of a blackbody cavity in radiative equilibrium. Thermal IR measurements such as those of Diviner can readily detect pit thermal signatures but would be insensitive to the existence of caves they may host, as the latter would only induce a 0.1 K increase to night‐time temperatures of the overlying surface. Plain Language Summary Since the discovery of pits on the Moon by JAXA's SELENE spacecraft in 2009, there has been interest in whether they provide access to caves that could be explored by rovers and astronauts. These features are likely created by the ceiling of a lava tube (or more generally, cave) collapsing. Using data from the Diviner instrument aboard the Lunar Reconnaissance Orbiter, which has been continuously measuring the temperature of the lunar surface for over 11 years, we thoroughly characterized the environment of one prominent pit. Located in Mare Tranquillitatis, the pit's thermal environment is more hospitable compared to anywhere else on the Moon, with temperatures varying minimally around a comfortable 17°C (or 63° F) wherever the Sun does not shine directly. If a cave extends from a pit such as this, it too would maintain this comfortable temperature throughout its length, varying by less than 1°C over an entire lunar day. Although we cannot be completely certain of a cave's existence through remote observations, such features would open the door for future exploration and habitation on the Moon: they could provide shelter from dramatic temperature variations present elsewhere on the lunar surface. Key Points Lunar pits stay warmer than the surface during the night, with the floor maintaining temperatures >230 K according to computational models Caves stemming from lunar pits would behave like blackbody cavities at ∼290 K and have nearly invariable temperatures far from the opening