Lunar Regolith Temperature as a Monitor of the Radiation Budget of Earth
Shaopeng Huang [shaopeng@umich.edu], Dept. of Geological Sciences, University of Michigan, Ann Arbor

Results from several spacecraft missions have greatly improved our understanding of the climate system of Earth. However, accurately detecting changes in solar irradiance and in the albedo and emission of Earth remains a challenging task. Lunar regolith temperatures may comprise important clues to deepening our understanding of the radiation budget of Earth. Locked in synchronous rotation, the Moon keeps one hemisphere (far-side) away from Earth and the other half (near-side) to Earth. Surface temperature on the far-side of the Moon is entirely controlled by solar irradiance, and is a faithful reflection of the solar radiation imposed on terrestrial climate system. On the near-side of the Moon, however, lunar surface temperature reflects changes both in incoming solar irradiance and in the outgoing energy flux from Earth. A review of six historical temperature time series at Apollo 15 landing site reveals that while daytime near-side temperature is controlled principally by direct solar irradiance, nighttime temperature is affected mainly by the reflected radiation and emission from Earth. Additionally, analysis of subsurface temperature measurements from boreholes on the Moon can extend the length of the lunar surface temperature history. Our understanding of temperature change of Earth prior to the existence of direct instrumental records relies on temperature proxies such as tree-rings, pollen, corals, isotopic ratios of atmosphere as preserved in ice cores or sediments, and borehole temperatures. Because of the absence of life and atmosphere on the Moon, subsurface temperature is the only known index that can be used for a reconstruction of a lunar surface temperature history.