PYTS 395B – Detecting Ice on the Moon 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

PYTS 395B – Detecting Ice on the Moon 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?

PYTS 395B – Detecting Ice on the Moon 3

PYTS 395B – Detecting Ice on the Moon 4

Feldman et al., 1998

PYTS 395B – Detecting Ice on the Moon 5

Bussey et al., 1999

PYTS 395B – Detecting Ice on the Moon 6

Margot et al., 1999

PYTS 395B – Detecting Ice on the Moon 7

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

PYTS 395B – Detecting Ice on the Moon 8

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

PYTS 395B – Detecting Ice on the Moon 9

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?