NASA 2001 Mars Odyssey page 1 Workshop HEND Russian Aviation and Space Agency Institute for Space Research Signatures of ground water from maps of neutron leakage flux measured by HEND Workshop “The First year of HEND operations on the NASA Odyssey Mars Orbiter” Moscow, Russia May 20-22, 2002

NASA 2001 Mars Odyssey page 2 Workshop HEND Russian Aviation and Space Agency Institute for Space Research M.Litvak, D.Anfimov, A.Kozyrev, I. Mitrofanov and A.Sanin (1 W.Boynton, D.Hamara and C.Shinohara (2 R.S.Saunders (3 1) Institute for Space Research, Moscow, Russia 2) University of Arizona, Tucson, USA 3) JPL, Pasadena, USA

NASA 2001 Mars Odyssey page 3 Workshop HEND Russian Aviation and Space Agency Institute for Space Research Galactic Cosmic Rays freely propagates through thin Martian atmosphere and produce neutrons, gamma-rays and X-rays in the 2-3 meters subsurface layer Their flux and energy spectra manifest the elementary composition of the “red planet” subsurface

NASA 2001 Mars Odyssey page 4 Workshop HEND Russian Aviation and Space Agency Institute for Space Research HEND was designed for detection of high energy neutrons from the Martian surface HEND has three detectors of neutrons based on proportional counters 3 He with thick (LD), medium (MD) and thin (SD) moderators, one scintillation detector for fast neutrons IN/SC and detector for anti-coincidence OUT/SC

NASA 2001 Mars Odyssey page 5 Workshop HEND Russian Aviation and Space Agency Institute for Space Research Sensitivity and Energy Ranges of HEND Detectors: LD: 10.0 eV MeV MD: 0.4 eV keV SD: 0.4 eV keV IN/SC/N: 850 keV – 15,0 MeV IN/SC/G:60 keV – 2.0 MeV OUT/SC:30 keV – 1.0 MeV

NASA 2001 Mars Odyssey page 6 Workshop HEND Russian Aviation and Space Agency Institute for Space Research Neutrons [0.4 eV – 100 keV]Neutrons [0.4 eV – 1 keV] OBSERVATIONS: 45 days mapping of Mars

NASA 2001 Mars Odyssey page 7 Workshop HEND Russian Aviation and Space Agency Institute for Space Research Neutrons [10 eV – 1 MeV]Neutrons [850 keV – 15 MeV] OBSERVATIONS: 45 days mapping of Mars

NASA 2001 Mars Odyssey page 8 Workshop HEND Russian Aviation and Space Agency Institute for Space Research COMPARISON: HEND and NS Epithermal neutrons registered by NS Epithermal neutrons registered by HEND

NASA 2001 Mars Odyssey page 9 Workshop HEND Russian Aviation and Space Agency Institute for Space Research RELIABILITY OF MEASUREMENTS Epithertmal neutrons   All proportional counters maps demonstrate the similar features.   All maps features are reproduced for different periods of measurements.   There is good correspondence between HEND epithermal neutrons maps and NS epithermal neutron map. Fast neutrons   The map created for Stilben detector demonstrates the similar features on South and around Tharsis Montes region as seen in proportional counters.   All map features are reproduced for different periods of measurements.

NASA 2001 Mars Odyssey page 10 Workshop HEND Russian Aviation and Space Agency Institute for Space Research Epithermal neutrons  The maximal counts rate is observed South-East from Tharsis Montes in the region around the point with coordinates (270°, -30°).   A huge depression is detected above the very large province at the Southern hemisphere with area S eth (S) ≈ 9.7· ּ 10 6 km 2 (South of -60° latitude).   Another depression, but with much smaller area S eth (N) ≈ 5·10 6 km 2 is observed in the Northern hemisphere to the North from Alba Patera around the point with coordinates (240°, +60°)   The lagest deficit in neutron flux is equal 10 times FEMENOLOGIAL RESULTS Fast neutrons  The maximal counts rate is observed South-East from Tharsis Montes in the region around the point with coordinates (270°, -30°).   A significant depression is detected above the small province at the Southern hemisphere with area S eth (S) ≈ 2.5· ּ 10 6 km 2 (South of -60° latitude).   A significant depression, but with much larger area S eth (N) ≈ ּ 10 7 km 2 is observed above the Northern hemisphere   The largest deficit in neutron flux is equal 3.3 times

NASA 2001 Mars Odyssey page 11 Workshop HEND Russian Aviation and Space Agency Institute for Space Research COMPARISON WITH EARTH MOON The maximal deficit of neutron flux seen on the Moon is less then 1.5 times. In case of Mars this value may reach 10 times.

NASA 2001 Mars Odyssey page 12 Workshop HEND Russian Aviation and Space Agency Institute for Space Research MODEL INTERPRETATIONS South pole Comparison of two deficits (3.3 and 10 times) of fast and epithermal neutron fluxes may be explained as following: We see layered subsurface which consists of layer of water ice positioned in the subsurface below a dry layer of SO 2 with the thickness ~70 cm North pole The deficit of fast neutron flux and the absence of significant deficit of epithermal neutron flux above North pole may be explained as following: We see homogeneous subsurface layer which contains about 5 percent of water.