High-Resolution Image

This figure shows changes in temperature in the Moon's sub-surface layer, the so-called "lunar regolith", plotted versus depth in the regolith at 80 degrees south latitude near south pole. The differences are with respect to a simple baseline profile that assumes a constant incoming solar heating of current level, while the 2 curves shown are adjustments to that baseline that would be measured for 2 scenarios of varying solar input. A reduction of 2W/m2 and 4W/m2 during the Maunder Minimum are used in scenario 1 (blue) and scenario 2 (red) respectively.

As lunar regolith is a good insulator, sub-surface temperature only responds to long-term variations of solar forcing, and records the history of lunar climate. Because of characteristics of the time delay in heat transport, the current lunar climate is directly related to historical variations of total solar irradiance (TSI). The e-folding penetration depth depends on the thermal properties of regolith and the time scale of variations of TSI. The depth where the maximum difference of temperature occurs determines the time scale of variations in TSI. The magnitude of the temperature difference from the baseline temperature gives the strength of variations in TSI. Thus, the historical variations of TSI can be derived from current lunar climate – borehole temperature profiles.

(submitted by Robert Cahalan & Guoyong Wen UMBC-GEST)