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"Cold Traps" and PSR Near South Pole of the Moon

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“COLD TRAPS” AND PSR NEAR SOUTH POLE OF THE MOON.
E A. Kozlova
1
, E. N. Lazarev
1
, A. A. Shangaraev
1
. Sternberg State Astronomical Institute, 119899, Mos-
cow, Russia; Email: katk@sai.msu.ru.
Introduction. It has long been known that in
the topographic depressions (for example in the
impact craters), located near the Moon’s poles,
there exist permanently shadowed regions (PSR)
[1] and the surface temperature in these regions
remain low for a prolonged period (billions of
years). Therefore, it was suggested that such re-
gions may contain volatiles such as water. Radar
studies [2] and detection of the regions of high
hydrogen content in the areas of impact craters,
made by Lunar Prospector spacecraft [3], con-
firmed these assumptions. Such craters as Shoe-
maker, Faustini, Shackleton, Haworth and Sver-
drup were called as the most likely candidates for
the role of “cold traps” for volatiles in the South
Pole region of the Moon. The most recent data
obtained by the neutron spectrometer of LEND
(LRO) showed the coincidence of the minima of
the neutron flux with areas of these craters [4].
Fig. 1. The illumination in the South Pole region
of the Moon. S – Shoemaker, F – Faustini, H
Haworth, Sc – Shackleton, Sv – Sverdrup, G – de
Gerlach.
“Cold traps” and PSR. The neutron spec-
trometer LEND aboard the LRO spacecraft has
detected an excess of hydrogen not only in the
PSR but outside them [4]. One possible explana-
tion of this may be that not only PSR can play
role of “cold traps”. The existence of volatiles in
the “cold traps” is determined by the tempera-
tures in these traps which are dependant on inso-
lation of given area. So PSR may not be a “cold
trap” if it is heated by an illuminated area. “Cold
traps” may also not be PSR if they are illuminated
by the Sun either when the Sun illuminates them
over a short period of time or at a low elevation
angle of the Sun above the Moon’s horizon.
We investigated the distribution of the tem-
perature and illumination in the South Pole region
of the Moon with data obtained by LRO (LOLA)
spacecraft [5].
Fig. 2. The distribution of maximum temperatures
in the South Pole area of the Moon.
Fig. 1 shows the “cold traps” (in blue) and
PSR (in red). The boundaries of the “cold traps”
are shown for T < 110 K (this is an upper tem-
perature limit for long-term presence of water ice
[6]). Fig. 2 shows the distribution of maximum
temperatures in the South Pole region of the
Moon.
All the above craters contain both PSR and
“cold traps”. At the same time PSR are situated
not only in craters but also between them: the
2039.pdf42nd Lunar and Planetary Science Conference (2011)
area between the Shoemaker crater and the Ha-
worth crater (area 1 on Fig. 1) is an example of
this. This area has been previously singled out as
permanently shadowed according to the
KAGUYA spacecraft data [7].
KAGUYA spacecraft data was applied for
three dimensional interpretation of the lunar
South Pole region relief (Fig. 3). PSR distribution
was superimposed with relief variation. There is
good correlation between illumination and relief
at this model and as follows from this model PSR
are located not only in the craters and on their
interior slopes but both between them and on the
outer ones respectively.
Fig. 3. 3D model of lunar South Pole region and
PSR superimposed.
The total area of PSR in the South Pole region
of the Moon is more than 600 sq. km. The total
area of “cold traps” exceeds this value and is
more than 800 sq. km.
References: [1]. Watson K. et al. (1961) JGR,
66, 3033. [2]. Margot J.L. et al., (1999) Science,
284, p.58-60. [3]. Feldman W.C. et al., (2001)
JGR, 102, 25565-25574. [4]. Mitrofanov I. G. et
al., (2010) Science, 330, 483-486. [5].
http://wwwpds.wustl.edu/ [6]. Vasavada A.R. et
al. (1999) Icarus, 141, 179-193. [7]. Kozlova
E.A. et. al (2010), Proceedings of ISLS2010, 183-
187.
2039.pdf42nd Lunar and Planetary Science Conference (2011)
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Hydrogen has been inferred to occur in enhanced concentrations within permanently shadowed regions and, hence, the coldest areas of the lunar poles. The Lunar Crater Observation and Sensing Satellite (LCROSS) mission was designed to detect hydrogen-bearing volatiles directly. Neutron flux measurements of the Moon’s south polar region from the Lunar Exploration Neutron Detector (LEND) on the Lunar Reconnaissance Orbiter (LRO) spacecraft were used to select the optimal impact site for LCROSS. LEND data show several regions where the epithermal neutron flux from the surface is suppressed, which is indicative of enhanced hydrogen content. These regions are not spatially coincident with permanently shadowed regions of the Moon. The LCROSS impact site inside the Cabeus crater demonstrates the highest hydrogen concentration in the lunar south polar region, corresponding to an estimated content of 0.5 to 4.0% water ice by weight, depending on the thickness of any overlying dry regolith layer. The distribution of hydrogen across the region is consistent with buried water ice from cometary impacts, hydrogen implantation from the solar wind, and/or other as yet unknown sources.
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