Mercury (and the Moon) possesses a tenuous atmosphere

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• Mercury (and the Moon) possesses a tenuous
  atmosphere

Calcium now also seen at Mercury

• Sodium emission at the Moon and Mercury shows
  temporal changes
• Stirring of regolith by small impacts

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• Evidence for ice in polar craters of Mercury
• Evidence for ice at lunar poles
• Clementine bi-static radar
• Lunar prospector neutron
• Evidence for ice at poles of Mercury
• VLA radar returns

• Sungrazing comets
• Kreutz group
• Source of water?

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Feldman et al., 1998
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Bussey et al., 1999
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Margot et al., 1999
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• Modeling (Vasavada et al. 1999) shows
  temperatures in permanently shadowed craters are
  very low
• These cold traps are favored condensation sites

Vasavada et al., 1999
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• Water leaves cold traps by sublimation
• 5-15 returns on Mercury
• 20-50 returns on the Moon
• The rest is lost
• Water can be delivered by meteors and comets
• For Mercury these rates have been estimated
• Balance exists if Tice is 113K

Killen et al., 1997
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• Lunar cold traps dry compared to Mercury
• Recent comet impact?
• Polar inconsistency?
• More H in lunar north pole
• More permanent shadows in lunar south pole
• Burial depth differences
• Dispersed grains?