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Mercury (and the Moon) possesses a tenuous atmosphere

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. Evidence for ice in polar craters of Mercury Evidence for ice at lunar poles

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Mercury (and the Moon) possesses a tenuous atmosphere

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  1. 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

  2. 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?

  3. Feldman et al., 1998

  4. Bussey et al., 1999

  5. Margot et al., 1999

  6. 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

  7. 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

  8. 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?

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