Physics
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....14044m&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #14044
Physics
Scientific paper
Maps of neutron emission from Mars will be presented based on data from the High Energy Neutron Detector (HEND) onboard “2001 Mars Odyssey”. HEND uses the classical technique of neutron detection. It contains three detectors with similar He3 proportional counters and different layers of moderation encapsulation, which cover the broad energy range of epithermal neutrons from 0.4 eV up to 1 MeV, and one sthylbene scintillation detector with 15 energy channels from 0.85 MeV up to >15 MeV. HEND is part of the Gamma-Ray Spectrometer suite together with the high purity Ge detector from University of Arizona in Tucson and the neutron spectrometer from Los Alamos National Laboratory. HEND operates synchronously with the GRS suite and has the same accumulation time intervals of about 20 seconds for pixelization. Neutron data were accumulated for the summer season in both the Northern and Southern hemisphere. The summer-time map of Mars displays two regions of strong depression of epithermal neutrons poleward from 55°-60° N and 60° S. Joint analysis of data for thermal, epithermal and high energy neutrons and for 2.2 MeV nuclear line of D indicates that this depression corresponds to the presence of an ice-rich layer with 35%-50% water below the top dryer layer 20-30 g/cm2 with about 3% of water. The summer-time map shows that Northern Permafrost and Southern Permafrost Regions cover together about 15% of the total Martian surface. In the north the content of water shows correlation with local elevation. The origin of permafrost with very high content of water is a major problem for geology and climatology of Mars. There are two additional regions of low abundance of epithermal neutrons: Arabia Moisture Region around 30° E and 10° N and Memnonia Moisture Region about antipodal to the first one at 200° E and 15° S. The content of water at these regions is about 5-7% by weight, which is close to the upper limit for chemically bound water in the soil. It is difficult to justify the alternative form of water in these equatorial regions, free ice, because ice is not expected to survive at the equatorial latitudes. The origin of water at these two moisture regions is discussed.
Boynton William
Drake Dan
Hamara Dave
Kozyrev A. S.
Litvak Maxim L.
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