Lunar heat flow: Regional prospective of the Apollo landing sites

Abstract

AbstractWe reexamine the Apollo Heat Flow Experiment in light of new orbital data. Using three‐dimensional thermal conduction models, we examine effects of crustal thickness, density, and radiogenic abundance on measured heat flow values at the Apollo 15 and 17 sites. These models show the importance of regional context on heat flux measurements. We find that measured heat flux can be greatly altered by deep subsurface radiogenic content and crustal density. However, total crustal thickness and the presence of a near‐surface radiogenic‐rich ejecta provide less leverage, representing only minor (<1.5 mW m−2) perturbations on surface heat flux. Using models of the crust implied by Gravity Recovery and Interior Laboratory results, we found that a roughly 9–13 mW m−2 mantle heat flux best approximate the observed heat flux. This equates to a total mantle heat production of 2.8–4.1 × 1011 W. These heat flow values could imply that the lunar interior is slightly less radiogenic than the Earth's mantle, perhaps implying that a considerable fraction of terrestrial mantle material was incorporated at the time of formation. These results may also imply that heat flux at the crust‐mantle boundary beneath the Procellarum potassium, rare earth element, and phosphorus (KREEP) Terrane (PKT) is anomalously elevated compared to the rest of the Moon. These results also suggest that a limited KREEP‐rich layer exists beneath the PKT crust. If a subcrustal KREEP‐rich layer extends below the Apollo 17 landing site, required mantle heat flux can drop to roughly 7 mW m−2, underlining the need for future heat flux measurements outside of the radiogenic‐rich PKT region.