Transcript ICE: On The Moon - Lunar and Planetary Laboratory

ICE:
On The Moon
Lindsay Johannessen
PTYS 395
All photos courtesy of
Vasavada el at., Feldman et al., Margot et al.,
www.nasa.gov, www.psrd.hawaii.edu,
http://apollo.sese.asu.edu
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, meterthick 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 regions
North 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.