An observation of lunar nighttime ions
Schneider, Henry Emil
Freeman, John W.
Master of Science
The Rice University Suprathermal Ion Detector Experiment deployed on Apollo missions 12, 14, and 15 regularly observes ion events all through the lunar night. The ion events are most often less than 4 hours in duration, and usually less than one hour. The energy spectra of the events vary from mono-energetic at 25 eV/q to 5 eV/q to fairly broad. The energy represented may range from 25 eV/q to 15 eV/q. There is some indication that the peak energy of the events increases from 5 eV/q at local sunset to 75 eV/q at about 3 days before local sunrise and then decreases to 25 eV/q 1 day before the sunrise terminator crossing. The ion energies are generally less than the solar wind and the ion flux (1 ions/cm -sec-ster) is down by 2 orders of magnitude from the solar wind. Ion activity increases in the period 1 to 6 days prior to local sunrise with a peak at 2 to 3 days before sunrise. There is also a weak secondary activity peak 3 to 4 days after local sunset. Data from the Apollo 12 SIDE has not been looked at yet. The Apollo 14 and Apollo 15 SIDE 's both exhibit the same activity profile. This fact suggests a local lunar time dependence rather than a position in orbit for the occurrence of these events.