Temperatures near the lunar poles and their correlation with hydrogen
predicted by LEND
Abstract
The lunar polar regions offer permanently shadowed regions (PSRs)
representing the only regions which are cold enough for water ice to
accumulate on the surface. The Lunar Exploration Neutron Detector (LEND)
aboard the Lunar Reconnaissance Orbiter (LRO) has mapped the polar
regions for their hydrogen abundance which possibly resides there in the
form of water ice. Neutron Suppression Regions (NSRs) are regions of
excessive hydrogen concentrations and were previously identified using
LEND data. At each pole we applied thermal modeling at three NSRs and
one unclassified region to evaluate the correlation between hydrogen
concentrations and temperatures. Our thermal model delivers temperature
estimates for the surface and for 29 layers in the sub-surface down to 2
m depth. As anticipated, we find the three south polar NSRs which are
coincident with PSRs in agreement with locations of hydrogen abundance
and their respective (near-)surface temperatures. Water ice is suspected
to be present in the upper ≈19 cm layer of regolith. The three north
polar NSRs however lie in non-PSR areas and are counter-intuitive as
such that most surfaces reach temperatures that are too high for water
ice to exist. However, we found that these areas offer ideal conditions
for ice pumping and suggest water ice to depths down to ≈35-65 cm. These
depths are observable by LEND and can, at least in part, explain the
existence and shape of the observed hydrogen signal. Although we can
substantiate the anticipated correlation between hydrogen abundance and
temperature the converse argument cannot be made.