Mission News

Water Abundances Change with Time of Day
Changes in the amounts of water and hydroxyl on the moon's north pole

Observations from NASA's Deep Impact mission of the moon's north pole from June 2 to 9, 2009 reveal changes in the amounts of water and hydroxyl. In the week between these datasets, the moon had rotated 90 degrees (one-quarter of a lunar day). For example, a volcanic mare terrain (labeled '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.

Deep Impact observed a significant change in the strength of a water and hydroxyl signature as the moon rotated around. The highland unit, for example, has a weaker signal near noon (red) and a stronger signal by evening (blue). Taken together, the data show a systematic change in water loss from morning to noon, recovery through the afternoon, and a return to a steady state by evening. This daytime cycle suggests that hydrogen ions in the solar wind may be a source for re-hydration.

Credit: NASA/JPL-Caltech/University of Maryland

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