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
changes.
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,
France.
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:
