A new look at Apollo 17 LEAM data: Nighttime dust activity in 1976

Abstract One of the unresolved enigmas from the Apollo era is the existence and characteristics of highly electrically charged dust floating above the lunar surface. Potential evidence for this hypothesized phenomenon came from the Lunar Ejecta and Meteorites (LEAM) experiment on Apollo 17. The LEAM instrument consisted of three sets of multi-coincidence dust sensors facing different directions. Recently, new arguments were raised ( O'Brien, 2011 ) that the signals recorded by LEAM may be caused by interferences from heater current switching, which occurred most frequently near sunrise and sunset. In order to shed light on this controversy a new look into the LEAM data was initiated within the Colorado Center for Lunar and Dust and Atmospheric Studies (CCLDAS) team of NASA's Lunar Science Institute (NLSI). The purpose of this analysis is to verify the earlier analysis by Berg et al. (1975) , and to find evidence for impacts of interplanetary meteoroids in the LEAM data available to us. A second goal is to find in the LEAM house keeping data evidence for excessive power switching and correlated signals in the LEAM science data. The original analysis by Berg et al. (1975) covered LEAM data during 22 lunations (~22 months) in 1973 and 1974. This data set is no longer available. For the present study, we had access to LEAM data for only about 5 lunations (140 days) in 1976. We analyzed the housekeeping data and observed excessive heating from about 24 h after sunrise until about 24 h before sunset. We defined sunrise and sunset when the LEAM temperature measurement reached −20 °C above which significant solar heating was apparent. For about 9 days around lunar noon the temperatures were so high that LEAM was switched off. During the times of excessive heating LEAM became very noisy. We limit our current analysis to about 24 h before sunset to about 24 h after sunrise when the LEAM temperatures were moderate