Other
Scientific paper
Jan 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998nvmi.conf...29f&link_type=abstract
Workshop on New Views of the Moon: Integrated Remotely Sensed, Geophysical, and Sample Datasets, p. 29
Other
Craters, Hydrogen, Ice, Water, Lunar Crust, Lunar Composition, Lunar Geology, Lunar Resources, Lunar Surface, Fast Neutrons, Lunar Prospector, Neutron Spectrometers, Solar Wind
Scientific paper
Although several theories have been proposed to explain the origin of the Moon, the present consensus favors birth initiated by a giant impact of the proto-Earth by a Mars-sized planetoid. If correct, the Moon was born depleted in volatiles, including H. Hydrogen embedded in regolith grains has been found in returned samples. This observation has been explained in terms of solar wind implantation, thereby providing one of several indicators of soil maturity. It has also long been speculated that H has been delivered to the Moon in the form of water ice by comets and asteroids. If the amount delivered in any one impact is sufficiently small so that a thick atmosphere does not form, then a sizable fraction (about 20%) will migrate to both poles through an exospheric transport process. In this case, if water molecules encounter spots that are sufficiently cold (primarily within permanently shaded craters near both poles), they will plate the surface where they can remain stably trapped for eons if the rate of loss due to a variety of processes does not overwhelm the rate of deposition. However, many comets are sufficiently large that a collisionally thick atmosphere should form. The migration of water molecules for these events has not been modeled, so the efficiency of deposition and the structure of the resultant deposits are not known. Many searches for deposits of water ice near both lunar poles have been conducted using radar backscatter data. To date, no such deposits have been found. A recent analysis of epithermal neutron data measured using the Lunar Prospector neutron spectrometer has provided a positive identification of enhanced deposits of H near both poles. Although a likely interpretation of these deposits is in terms of water-ice trapped within permanently shaded craters, other interpretations that of the migration of solar wind H cannot be ruled out at this time. A preliminary analysis of fast neutron data, also measured using the Lunar Prospector neutron spectrometer, provides only an upper limit to the signature expected for surface deposits of H near the poles. A consistent interpretation of all three datasets (epithermal neutrons, radar backscatter, and fast neutrons) is possible if water ice does indeed reside in permanently shaded craters near both poles, but is buried beneath a few tens of centimeters of dry regolith. We will discuss the neutron measurements and their interpretation. We will also discuss advances that can be made by correlating Lunar Prospector data with information returned using other techniques to define the total area contained within permanently shaded craters near both poles.
Barraclough Bruce L.
Binder Alan B.
Elphic Rick C.
Feldman William C.
Lawrence D. Jr. J.
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