Global Distribution of Neutrons from Mars: Results from Mars Odyssey

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 CO2 in the uppermost meter of the martian surface. Poleward of +/-60 degrees 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.

Introduction to the 4th Mars Polar Science and Exploration Conference special issue: Five top questions in Mars polar science

“…These theoretical expectations appear consistent with measurements of the near-surface (top ∼0.5 m) regolith hydrogen abundance made by the Mars Odyssey Gamma Ray Spectrometer (GRS) (Boynton et al, 2002;Feldman et al, 2002). The GRS data are usually interpreted in the context of a simple 2-layer model, wherein ice-rich (>60% by volume) regolith is assumed to underlie a desiccated layer of variable thickness.…”

Searching for signatures of life on Mars: an Fe-isotope perspective

“…The gamma ray spectrometer onboard NASA's Odyssey spacecraft has also detected abundant hydrogen within the 1 m subsurface regions beyond 60 8N and S of the equator (e.g. Feldman et al 2002). The hydrogen atoms have been interpreted to be present as H 2 O constituting a large subsurface reservoir of water on Mars.…”

Scalloped terrains in the Peneus and Amphitrites Paterae region of Mars as observed by HiRISE

“…In 2002, GRS data, which are directly dependent on the concentrations of hydrogen, and therefore almost certainly upon the concentration of water, within roughly one meter of the surface, showed the presence of extensive ground ice within this upper meter above $50°latitude in both hemispheres (Feldman et al, 2002;Boynton et al, 2002;Mitrofanov et al, 2002); concentrations typically range from $2 to 5 wt% at $40°l atitude to $20 wt% at 60°latitude, generally increasing polewards . Ice-stability models, which are consistent with the GRS observations, show that ground ice within a meter, or less, of the surface should generally be stable above 45-55°lat-itude (e.g., Mellon and Jakosky, 1993;Allen and Kanner, 2007).…”