Water vapor, whence comest thou.

During a 14-hour period on Mar. 7, 1971, the Apollo 14 ALSEP suprathermal ion detector experiment (SIDE) observed an intense, prolonged series of bursts of 48.6-eV ions at the lunar surface. The SIDE mass analyzer showed the mass per unit charge of these ions to be characteristic of water vapor if singly ionized. The event was also observed by the SIDE total ion detectors (TIDs) at the Apollo 14 site and at Apollo 12 (located 183 km to the west). The TID data from SIDE 14 indicate that the energy spectrum was narrower than the 20-eV interval between energy channels. Ion spectra due to the LM exhaust gases are shown to be readily identified by the SIDE and are distinctly different in character from the spectra obtained on March 7. Detailed consideration of other possible sources of water, including the Apollo 14 CSM, leads to the conclusion that the water vapor did not come from a man-made source. Also, it is estimated that the event may have involved a quantity of water much greater than that which has been artificially introduced into the lunar environment. Consequently, it appears to be of lunar origin.