In a new study, researchers, including Dr. Walter Kiefer at the Lunar and Planetary Institute (LPI), recovered and restored unarchived data from the Apollo heat flow experiment (HFE) conducted on the Moon in the 1970s. The newfound data filled in the missing gaps which aided researchers in pinpointing the cause of the warming observed on the lunar surface.
The Apollo HFE was conducted at the Apollo 15 and 17 landing sites. Heat flow probes were deployed as part of the Apollo Lunar Surface Experiments Package (ALSEP). The probes monitored surface and subsurface temperature at different depths from 1971 to 1977. The original HFE investigators noted the temperature of the regolith rose gradually through December 1974 at both sites. The restored data showed the subsurface warming continued until the end of observations in 1977. The new study concludes that the astronauts’ activities caused the regolith to become slightly darker. As a result, solar heat absorbed by the regolith increased slightly on average, which produced the observed warming. This study has implications for future lunar-landing missions and will influence our approach to heat flow probe deployment and measurement methodologies.