NASA’s Mars Odyssey spacecraft is revealing new details
about the intriguing, dynamic character of the frozen layers
now known to dominate the high northern latitudes of Mars.
The implications have a bearing on science strategies for
future missions in the search of habitats.

Odyssey’s neutron and gamma ray sensors tracked seasonal
changes as layers of “dry ice” (carbon-dioxide frost or
snow) accumulated during northern Mars’ winter and then
dissipated in the spring, exposing a soil layer rich in
water ice, the Martian counterpart to permafrost.
Researchers used measurements of Martian neutrons, combined
with height measurements from the laser altimeter on another
NASA spacecraft, Mars Global Surveyor, to monitor the amount
of dry ice during the northern winter and spring seasons.

“Once the carbon-dioxide layer disappears, we see even more
water ice in northern latitudes than Odyssey found last year
in southern latitudes,” said Odyssey’s Dr. Igor Mitrofanov
of the Russian Space Research Institute, Moscow, lead author
of a paper in the June 27 issue of the journal Science. “In
some places, the water-ice content is more than 90 percent
by volume,” he said. Mitrofanov and co-authors used the
changing nature of the relief of these regions, measured
more than two years ago by the Global Surveyor’s laser
altimeter science team, to explore the implications of the

  • 27 June 2003: Morphology and Composition of the Surface of Mars: Mars Odyssey THEMIS Results, Science
  • 27 June 2003: CO2 Snow Depth and Subsurface Water-Ice Abundance in the Northern Hemisphere of Mars, Science
  • 27 June 2003: The Surface of Mars: Not Just Dust and Rocks, Science
  • Mars Odyssey’s trio of instruments, the gamma ray
    spectrometer suite, can identify elements in the top meter
    (three feet) or so of Mars’ surface. Mars Global Surveyor’s
    laser altimeter is precise enough to monitor meter-scale
    changes in the thickness of the seasonal frost, which can
    accumulate to depths greater than a meter. The new findings
    show a correlation in the springtime between Odyssey’s
    detection of dissipating carbon dioxide in latitudes pole
    ward of 65 degrees north and Global Surveyor’s measurement
    of the thinning of the frost layer in prior years.

    “Odyssey’s high-energy neutron detector allows us to measure
    the thickness of carbon- dioxide at lower latitudes, where
    Global Surveyor’s altimeter does not have enough
    sensitivity,” Mitrofanov said. “On the other hand, the
    neutron detector loses sensitivity to measure carbon-dioxide
    thickness greater than one meter, where the altimeter
    obtained reliable data. Working together, we can examine the
    whole range of dry ice snow accumulations,” he said.

    “The synergy between the measurements from our two ‘eyes in
    the skies of Mars’ has enabled these new findings about the
    nature of near-surface frozen materials, and suggests
    compelling places to visit in future missions in order to
    understand habitats on Mars,” said Dr. Jim Garvin, NASA’s
    Lead Scientist for Mars Exploration.

    Another report, to be published in the Journal of
    Geophysical Research-Planets, combines measurements from
    Odyssey and Global Surveyor to provide indications of how
    densely the winter layer of carbon-dioxide frost or snow is
    packed at northern latitudes greater than 85 degrees. The
    Odyssey data are used to estimate the mass of the deposit,
    which can then be compared with the thickness to obtain a
    density. The dry ice layer appears to have a fluffy texture,
    like freshly fallen snow, according to the report by Dr.
    William Feldman of Los Alamos National Laboratory, N.M., and
    11 co-authors. The study also found once the dry ice
    disappears, the remaining surface near the pole is composed
    almost entirely of water ice.

    “Mars is constantly changing,” said Dr. Jeffrey Plaut, Mars
    Odyssey project scientist at JPL. “With Mars Odyssey, we
    plan to examine these dynamics through additional seasons,
    to watch how the winter accumulations of carbon dioxide on
    each pole interact with the atmosphere in the current
    climate regime,” he said.

    Mitrofanov’s co-authors include researchers at the Institute
    for Space Research, Russian Academy of Science, Moscow; MIT,
    Cambridge, Mass.; NASA’s Headquarters and Goddard Space
    Flight Center (GSFC), Greenbelt, Md.; and TechSource, Santa
    Fe, N.M. Feldman’s co-authors include researchers at New
    Mexico State University, Las Cruces; Cornell University,
    Ithaca, N.Y.; and Observatoire Midi-Pyrenees, Toulouse,

    JPL manages the Mars Odyssey and Global Surveyor missions
    for NASA’s Office of Space Science, Washington.
    Investigators at Arizona State University, the University of
    Arizona, and NASA’s Johnson Space Center, Houston, built and
    operate Odyssey science instruments. The Russian Aviation
    and Space Agency supplied the high-energy neutron detector
    and Los Alamos National Laboratory supplied the neutron
    spectrometer. GSFC supplied Global Surveyor’s laser
    altimeter. Information about NASA’s Mars exploration program
    is available on the Internet at: