Deep Impact observations of the north pole (June 2 and 9, 2009) separated by one week, or 1/4 of a lunar day reveal variations in the strength of the OH/H2O absorptions with time-of-day. For example, a mare unit (‘M’) is observed in the morning on June 2, but by June 9 is at local noon. Similarly, a highland unit (‘H’) begins at noon and rotates to evening on June 9. A significant change in the strength of the OH/H2O absorptions is observed, for example, for the highland unit, which has weaker/narrow absorptions near noon (red) and stronger/broader absorptions by evening (blue). Taken together these Deep Impact data show a systematic change with water loss from morning to noon, recovery through the afternoon, and a return to steady state by evening. This cycle requires a daytime source for rehydration and is therefore consistent with solar wind.
NASA/University of Maryland