ICE: On The Moon Lindsay Johannessen PTYS 395 All photos courtesy of Vasavada el at., Feldman et al., Margot et al.,

Ice: How would water ice get to the Moon? - Impactors: Comets, Meteors ect… These would have a great amount (or release a great amount) of water ice onto the Moon. - Solar Wind Sputtering: creating water ice in the exopshere.

What happens to this water ice when its deposited there? - They bounce around for a while until one of the following happens: - Bounce around the exopshere in ballistic trajectories for however long they can survive (being destroyed in a number of ways like photodissociation, solar-induced desorption etc…) - Eventually land in a safe, permanently shaded area of the North or South pole regions of the Moon.

- Studies show that approximately 20 – 50% of accumulated water deposits on the Moon should be settled as ice. - Here, we see the evaporation rate as a function of temperature

Where can this water ice form? - Subsurface ice is referenced to be stable within 2° of latitude from the poles, meter- thick ice will be located no further than 13° from the poles (Vasavada et al.) - Only in constantly shadowed areas will this water ice have a chance to accumulate (crater floors and walls, crescent shadow regions).

Shadowing on the Moon - In this image, we see how the effective shadow on the left side could potentially house water ice in the crater walls and shadowed floor. (Image not of polar region)

If there is ice, how much could be there? - Approximately 1850 km² around each polar region. (3700 km² in entirety) - Possible depth of up to 2 meters in certain accumulations. - All in all, each region could contain up to 3 X 10⁹ metric tons of water ice. - Possible depths reach to that under a regolith layer of up to 40 cm.

What are the theories? (How did we find out?) - First, we see what areas are permanently shaded on the Moon. - Analyze data taken from the LP spacecraft measuring hydrogen detection from a neutron spectrometer in polar regions. - Compare data collected from other known icy bodies, such as Comets and meteors.

Survival… - If there is water ice on the moon, under what circumstances would it need to ‘survive’? - Constant shadowing from solar radiation - Protection by a regolith layer - It is necessary to have a good understanding of the topography of the Moon’s poles. - Scientists use a dual radar inferometer to measure slopes of lunar topography.

Discrepancies: - Different researchers predict different latitudes for stable water ice at the poles: - Vasavada et al. say no more than 2°. - Nozette et al. say up to 2.5°, in agreement with Margot et al. and Feldman et al. - Shadowed regions versus hydrogen data? - South pole regions have more constantly shadowed regions than the north. - However, north pole regions have more hydrogen data.

- This implies that the hydrogen in the north polar regions may not be associated with any kind of water ice. South Pole regionsNorth Pole regions

More discrepancies… - Can we really detect further than one meter through regolith? - Are there Layers? Cold traps have been pixilated in white (north pole at top, south at bottom.

Current Studies: - LCROSS (Lunar Crater Observation and Sensing Satellite) will be launched this October. It will send out a probe into one of the possible icy areas of the Moon and a flyby secondary craft will gather data from the impact.