Global Distribution of Neutrons from Mars: Results from Mars Odyssey

TLDR

Neutron fluxes map the vertical and lateral distribution of hydrogen and CO₂ in the top meter of Mars’s surface. Mapping of thermal, epithermal, and fast neutron fluxes reveals hydrogen‑rich terrain poleward of ±60° latitude, likely buried H₂O ice, thick CO₂ layers covering the central north polar cap and residual south polar cap, and subsurface H₂O/OH deposits at low to middle latitudes.

Abstract

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 CO 2 in the uppermost meter of the martian surface. Poleward of ±60° latitude is terrain rich in hydrogen, probably H 2 O ice buried beneath tens of centimeter-thick hydrogen-poor soil. The central portion of the north polar cap is covered by a thick CO 2 layer, as is the residual south polar cap. Portions of the low to middle latitudes indicate subsurface deposits of chemically and/or physically bound H 2 O and/or OH.