The neutron and gamma-ray spectrometers aboard Mars Odyssey are being used to map the Martian near-surface water-equivalent hydrogen abundance. At the present time, analyses of neutron flux intensities in three distinct energy bands are providing the major source of our current knowledge of the hydrogen distribution because of their enhanced sensitivity. After just more than half a Martian year, we have been able to view both poles of Mars without obstruction by the seasonal dry ice polar cap. This view has revealed extensive deposits of water-ice rich soils that average about 50 weight percent by mass poleward of about 55deg. Although our present information is not sufficient to provide a unique description of the abundance and stratigraphy of these deposits, parts of each 600 km-diameter footprint of the neutron spectrometer appear to contain water ice within a few cm of the surface and other parts appear to be buried beneath 10 to 20 cm of relatively dessicated soils. Water-equivalent hydrogen is also present at mid-latitudes. The distribution maximizes in Arabia Terra and its antipode but spans the range between 2% and 11% by mass. All of the enhanced deposits extend to, or just below the surface and generally occur south of the dichotomy boundary.

We will show the first global maps of hydrogen on Mars at this talk and provide minimum estimates from them of the total amount of water that is stored at and below the surface of Mars. These estimates depend on assumptions of how these deposits were emplaced and retained. However, if, as some theories predict, they extend to 1 km beneath the surface, their total water content may be sufficient to account for the missing water budget of Mars.