 |
| Titel |
Lunar Polar Areas of Water-Rich Permafrost According to LEND/LRO Data |
| VerfasserIn |
Igor Mitrofanov, Maxim Litvak, Anton Sanin |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250049980
|
|
|
|
|
|
| Zusammenfassung |
| Introduction: Discovery of “New Polar Moon”. The main signature of
“New Polar Moon” is the presence of rather high content of water and
another volatiles in the polar regolith. The first possible detection
of water ice in polar craters has been claimed by the radar team of
Clementine mission. Non-direct evidence for the presence of water ice
in polar regolith was provided by Lunar Prospector Neutron
Spectrometer (LPNS), as extended suppressions of neutrons emission
around lunar poles. The first direct detection of H2O and/or OH in the
top layer of polar regolith was performed by IR mapping spectrometer
M3 onboard Chandraiaan-1 mission, but IR data characterizes the upper
most layer of few microns only.
The final proof for the presence of local areas with high content of
water and another volatiles at lunar poles has been recently provided
by direct measurements of NASA’s LRO and LCROSS missions: orbital
neutron telescope LEND of LRO has identified the crater of Cabeus, as
the most promising impact site with high content of hydrogen, and
instruments onboard LRO and LCROSS have measured direct signatures of
water, H2 and another volatiles in the plume material from the
artificial impact crater.
Observations: local water-rich areas at lunar poles, as Neutron
Suppression Regions (NSRs). Currently available neutron data from LEND
allowes identification of several local areas around both lunar poles,
which might have rather high content of water ice about several
percent by mass within 1 meter of the subsurface. They are detected
as Neutron Suppression Regions, or NSRs.
Questions to be addressed about “New Polar Moon”: There are several
questions about water-linked processes at recently found NSRs, which
shall be addressed in the presented talk:
(1) Which combination of physical conditions is necessary for a local
area at lunar pole to become NSR with permanent water ice in the
shallow subsurface? Initially one thought that permanent shadow could
be a sufficient condition for deposition and preservation of water ice
in regolith. Current experimental data does not support such a simple
idea; many PSRs do not manifest suppression of epithermal neutrons,
and there are cases, when NSR have illuminated surface.
(2) What is the origin of water in NSRs? One hypothesis assumes that
water was delivered to the Moon by comets. The hypothesis of “comet
water” was generically related with the model of PSRs, as “cold traps”
for water vapor from the post-impact transient atmosphere. “Comet
water” was delivered in separate impact episodes, and one has to
explain current location of water in NSRs by time history of these
events. The second hypothesis proposes that lunar water is
continuously produced in chemical reactions in regolith between
implanted protons of solar wind and oxygen of the soil.
(3) Which process could transport water molecules over the surface
from the place of initial release to the site of deposition? Detection
of local NSRs with enhancement of hydrogen and/or water points out
that there should be some mechanism of “horizontal migration”, which
delivers molecules toward some particular places of deposition on the
lunar surface..
(4) How could water propagate down to lunar subsurface? The presence
of water in the regolith in sun-lit conditions points out that ice is
the most likely preserved in the permanently cold layer of permafrost,
which is covered by dry regolith, which temperature varies according
to diurnal cycle of solar irradiation. Some kind of “vertical
migration” transport should be considered for explanation of NSR
formation, which brings water from the surface down to cold layer of
permafrost. |
|
|
|
|
|
|