HYDROGEN MEASUREMENTS
This is a map of data obtained by the epithermal neutron spectrometer (NS). Blue indicates low counts, and red indicates high counts. This data can be used to infer the presence of hydrogen. The counts received by the NS are inversely proportional to the amount of hydrogen, so that in fact, blue denotes areas of high concentrations of hydrogen.
In the polar regions, the hydrogen concentrations are associated with water ice. Elsewhere, at lower latitudes, the hydrogen detected is thought to be mainly from the solar wind. Water ice exists at the poles at the bottom of permanently-shadowed craters, in the form of pockets buried beneath 50 cm or so of dry regolith (a mixture of fine dust and rocky material produced by meteorite impacts). Current estimates are that about 3 billion metric tons of water ice exist at each of the poles.
The NS can detect hydrogen (water) to a depth of half a meter (1.5 feet). Meteor impacts over the last 2 billion years have tilled the soil to a depth of two meters, so that it is possible that water ice may exist two meters deep. If the water is in the form of ice crystals mixed with the regolith, pure water-ice deposits could potentially exist at much greater depths. Further analysis, as well as data from the Gamma Ray Spectrometer, will help mission scientists determine the precise distribution of water ice.
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