The Distribution of Hydrogen on Mars Bill Feldman

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The Distribution of Hydrogen on Mars Bill
Feldman
A major goal of the NASA and ESA space programs
is to find evidence for extraterrestrial life.
A prime requirement for the genesis and support
of life as we know it is water. A determination
of the distribution of water on Mars has
therefore been a prime objective of all missions
to Mars.
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Key Science Questions
What is the Water Inventory on Mars What is the
Geographic Distribution of Martian Water What
is the Form of Water on Mars Is there an Aquifer
What does the Water Abundance Distribution
Tell us about Climate Change on Mars
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Topography Map
Northern Plains
Olympus Mons
Valles Marinaris
Tharsis
Hellas Basin
Argyre
Southern Highlands
Mars Orbiter Laser Altimeter
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RiverbedsonMars
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This view of Gusev shows that Mars surface is
heterogeneous and dry
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Once an Ocean on Mars?
Where is All the Water Now?

• Hidden Ice
• Escaped the planet
• Chemically incorporated
• Deep down hydrosphere

Topography MOLA Team
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Movement of H2O and Ice by Obliquity
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The process of learning anything about planets is
not exact. One must first choose to measure a
quantity that is related to a phenomenon of
interest. One then chooses a model of the
environment that allows the translation of that
measurement to physical reality. Oftentimes the
chosen model does not mirror the actual
environment and/or contains parameters that are
not known. The only way out of this predicament
is to compare the new measurements with those
made using other methods in the hopes of getting
a clearer picture of the actual physical
conditions on and below the ground.
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Natural radiation from planetary bodies can
be used to determine the composition of their
outermost layers
Gamma rays (Fe, Mg, Ti, Si, O, Al, Ca, K, Th, U)
g
Thermal and epithermal neutrons (H, C, GdSm)
Cosmic ray
g
Fast neutron ltAtomic numbergt
g
Inelastic collision
Neutron capture
Th
Moderation (neutrons loose energy in successive
collisions, eventually achieving thermal
equilibrium with the surface)
Natural radioactivity
Fast neutrons
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Simulated Neutron leakage energy spectra for a
range of soil water content
Flux x Energy
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• The Mars Odyssey Neutron Spectrometer (MONS) was
  designed to detect and map deposits of hydrogen
  on Mars.
• The detector measures escaping neutron currents
  in three energy ranges, Thermal, Epithermal, and
  Fast.
• These currents can be used to constrain three
  parameters of a simple 1-D model of
  Water-Equivalent Hydrogen (WEH) distributions if
  the elemental composition of matrix soil material
  is known.
• These parameters are the WEH content of an upper
  layer, Wup, the thickness of this layer, D, and
  the WEH content of an assumed semi-infinite lower
  layer, Wdown.
• Our analysis proceeds in two steps the first
  assumes only one layer, D 0, which gives a
  lower bound to the WEH abundance, and the second
  expands to two layers.

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Spirit Wheel Track from Tyrone to
Winterhavenshowing white evaporite layer covered
by dust
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Water-Equivalent Hydrogen abundance of the lower
layer in a two-layer model of the near surface
regolith
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Polar projections of the WEH content of the lower
layer with a low abundance cutoff of 5 weight .
The region south of -75º is omitted to avoid
contamination by high thermal neutron currents
from the south polar residual, CO2-covered
water-ice cap
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Observed WEH near the equator is consistent with
recharge
from the atmosphere
Distribution of WEH observed using MONS
-60 0 60
H2O in atmosphere is centered north of the
equator
Latitude
-60 0 60
Atmospheric H2O emplacement using Ames MGCM -
close to the observed pattern of WEH
-60 0 60
180
-180
Longitude
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• Peak WEH is in the north
• Cut off from south residual cap by deep boundary
  canyons.

Solis Planum and Tempe Terra
Argyre and Xanthe Terra
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Comparison between longitude scans of the WEH of
the lower layer, and burial depths for five
latitudes between 60º and 70º north and south
latitudes. These scans can be separated into
three longitudinal sectors. Each has a relative
maximum and relative minimum in WEH(dn), and a
relatively flat portion, identified by the
horizontal lines.
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Anticorrelation between WEH (down) and burial
depth The correlation is good with a zero-depth
asymptote of WEH0.92
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Mangold, Icarus, 2005
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Beacon Valley, Marchant et al., 2002
60.7o N, -2.9o E, Mars Mangold et al., 2002
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Mellon et al., 2007
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HiRISE image of patterned ground at 69º N and
130º E.
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Burial Depth MONS Thermal- Epithermal Data
Patterned Ground Mangold et al., 2004
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Icy textures

• Sand vs. ice-wedge polygons, evidence of freeze
  thaw, deformation of icy material

Ice lenses
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Summary of Single-Layer Results

• Mars has two distinct domains of hydrogen large
  deposits at high latitudes and more modest, yet
  significant deposits near the equator.
• 2. Atmospheric H2O is concentrated generally
  north of the equator.
• WEH is found preferentially on north-facing
  slopes of northern
• portions of highest terrain in the southern
  highlands.
• 4. The pattern of H2O deposition predicted by
  the Ames MGCM is
• generally similar to the observed
  distribution of WEH.
• 5. WEH near the equator appears to be delivered
  through the
• atmosphere, not an aquifer fed by the southern
  water-ice cap.
• 6. At high latitudes, WEH is high and most
  likely exists as water ice.

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Summary of Two-Layer Results

• 1. The WEH abundance of the top layer is in the
  range between 1 and 5 by mass, but is generally
  closer to 2 by mass on average.
• 2. The WEH abundance in the lower layer generally
  increases with increasing latitude between 55o
  and 75o. The lone exception is in Scandia Colles
  in the north and Promethei Terrae in the south.
• 3. The apparent burial depth decreases with
  increasing latitude poleward of 60o in both
  hemispheres.
• 4. Zonal bands of high apparent burial depth at
  /- 60o are consistent with a transition from WEH
  contained in hydrous minerals at lower latitudes,
  to WEH in water ice and water of hydration at
  higher latitudes.
• 5. The anticorrelation between WEH (down) and
  Depth at high latitudes suggests that average
  regolith pore volumes decrease with increasing
  depth.