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Lunar and Planetary Institute

LPI Contributes to Solving Moon Mystery

June 13, 2018

Apollo heat flow experiment


In a new study published in the Journal of Geophysical Research: Planets, 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 landing sites 15 and 17. 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 probe deployment and measurement methodologies.

For more information, visit:

Examination of the Longā€Term Subsurface Warming Observed at the Apollo 15 and 17 Sites Utilizing the Newly Restored Heat Flow Experiment Data From 1975 to 1977

Scientists solve lunar mystery with aid of missing Moon tapes

ALSEP Document Repository

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