Global distribution of neutrons from Mars: Results from Mars Odyssey

Global distributions of thermal, epithermal, and fast neutron fluxes have been mapped during late southern summer/northern winter using the Mars Odyssey Neutron Spectrometer. These fluxes are selectively sensitive to the vertical and lateral spatial distributions of H and CO₂ in the uppermost meter of the martian surface. Poleward of ±60° latitude is terrain rich in hydrogen, probably H₂O ice buried beneath tens of centimeter-thick hydrogen-poor soil. The central portion of the north polar cap is covered by a thick CO₂ layer, as is the residual south polar cap. Portions of the low to middle latitudes indicate subsurface deposits of chemically and/or physically bound H₂O and/or OH.