Apollo lunar heat flow experiment revisited: A critical reassessment of the in situ thermal conductivity determination
Article first published online: 20 NOV 2010
Copyright 2010 by the American Geophysical Union.
Journal of Geophysical Research: Planets (1991–2012)
Volume 115, Issue E11, November 2010
How to Cite
2010), Apollo lunar heat flow experiment revisited: A critical reassessment of the in situ thermal conductivity determination, J. Geophys. Res., 115, E11005, doi:10.1029/2010JE003612., , and (
- Issue published online: 20 NOV 2010
- Article first published online: 20 NOV 2010
- Manuscript Accepted: 19 AUG 2010
- Manuscript Revised: 29 JUL 2010
- Manuscript Received: 29 MAR 2010
- heat flow;
- thermal conductivity
 Lunar heat flow was determined in situ during the Apollo 15 and 17 missions, but some uncertainty is connected to the value of the regolith's thermal conductivity, which enters as a linear factor into the heat flow calculation. Different approaches to determine the conductivity yielded discordant results, which led to a downward correction of the obtained heat flow values by 30%–50% subsequent to the publication of the first results. We have reinvestigated likely causes for the observed discrepancies and find that neither poor coupling between the probe and regolith nor axial heat loss can explain the obtained results. Rather, regolith compaction and compression likely caused a local increase of the regolith's thermal conductivity by a factor of 2–3 in a region which extends at least 2–5 cm from the borehole wall. We conclude that the corrected lunar heat flow values, which are based on thermal diffusivity estimates sampling a large portion of undisturbed regolith, represent robust results. Future in situ measurements of regolith thermal conductivity using active heating methods should take care to both minimize regolith disturbance during probe emplacement and maximize heating time to obtain reliable results. We find that for the Apollo measurements, heating times should have exceeded at least 100 h, and ideally 200 h.