Russian Aviation and Space Agency

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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
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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
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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
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HEND was designed for detection of high energy
neutrons from the Martian surface
HEND has three detectors of neutrons based on
proportional counters 3He with thick (LD), medium
(MD) and thin (SD) moderators, one scintillation
detector for fast neutrons IN/SC and detector for
anti-coincidence OUT/SC
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Sensitivity and Energy Ranges of HEND
Detectors LD 10.0 eV - 1.0
MeV MD 0.4 eV -100.0 keV
SD 0.4 eV - 1.0 keV IN/SC/N
850 keV 15,0 MeV IN/SC/G 60 keV 2.0 MeV
OUT/SC 30 keV 1.0 MeV
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OBSERVATIONS 45 days mapping of Mars
Neutrons 0.4 eV 100 keV
Neutrons 0.4 eV 1 keV
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OBSERVATIONS 45 days mapping of Mars
Neutrons 10 eV 1 MeV
Neutrons 850 keV 15 MeV
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COMPARISON HEND and NS
Epithermal neutrons registered by NS
Epithermal neutrons registered by HEND
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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.

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FEMENOLOGIAL RESULTS

• 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 Seth(S) 9.7?106km2 (South of -60
  latitude).
• Another depression, but with much smaller area
  Seth(N) 5106 km2 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

• 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 Seth(S) 2.5?106 km2 (South of -60
  latitude).
• A significant depression, but with much larger
  area Seth(N) ?107 km2 is observed above the
  Northern hemisphere
• The largest deficit in neutron flux is equal 3.3
  times

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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.
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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
SO2 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.