Odyssey Finds Water Ice in Abundance Under
Mars' Surface
May 28, 2002
Using instruments on NASA's 2001 Mars Odyssey spacecraft, surprised
scientists have found enormous quantities of buried treasure lying just
under the surface of Mars-enough water ice to fill Lake Michigan twice
over. And that may just be the tip of the iceberg.
"This is really amazing. This is the best direct evidence we have of
subsurface water ice on Mars. We were hopeful that we could find evidence
of ice, but what we have found is much more ice than we ever expected,"
said William Boynton, principal investigator for Odyssey's gamma ray spectrometer
suite at the University of Arizona, Tucson.
Scientists used Odyssey's gamma ray spectrometer instrument suite to
detect hydrogen, which indicated the presence of water ice in the upper
meter (three feet) of soil in a large region surrounding the planet's south
pole. "It may be better to characterize this layer as dirty ice rather
than as dirt containing ice," added Boynton. The detection of hydrogen
is based both on the intensity of gamma rays emitted by hydrogen, and by
the intensity of neutrons that are affected by hydrogen. The spacecraft's
high-energy neutron detector and the neutron spectrometer observed the
neutron intensity.
The amount of hydrogen detected indicates 20 to 50 percent ice by mass
in the lower layer. Because rock has a greater density than ice, this amount
is more than 50 percent water ice by volume. This means that if one heated
a full bucket of this ice-rich polar soil it would result in more than
half a bucket of water.
The gamma ray spectrometer suite is unique in that it senses the composition
below the surface to a depth as great as one meter. By combining the different
type of data from the instrument, the team has concluded the hydrogen is
not distributed uniformly over the upper meter but is much more concentrated
in a lower layer beneath the top-most surface.
The team also found that the hydrogen-rich regions are located in areas
that are known to be very cold and where ice should be stable. This relationship
between high hydrogen content with regions of predicted ice stability led
the team to conclude that the hydrogen is, in fact, in the form of ice.
The ice-rich layer is about 60 centimeters (two feet) beneath the surface
at 60 degrees south latitude, and gets to within about 30 centimeters (one
foot) of the surface at 75 degrees south latitude.
"Mars has surprised us again. The early results from the gamma ray spectrometer
team are better than we ever expected," said R. Stephen Saunders, Odyssey's
project scientist at NASA's Jet Propulsion Laboratory (JPL), Pasadena,
Calif. "In a few months, as we get into Martian summer in the northern
hemisphere, it will be exciting to see what lies beneath the cover of carbon
dioxide dry-ice as it disappears."
"The signature of buried hydrogen seen in the south polar area is also
seen in the north, but not in the areas close to the pole. This is because
the seasonal carbon dioxide (dry ice) frost covers the polar areas in winter.
As northern spring approaches, the latest neutron data indicate that the
frost is receding, revealing hydrogen-rich soil below," said William Feldman,
principal investigator for the neutron spectrometer at Los Alamos National
Laboratories, New Mexico.
"We have suspected for some time that Mars once had large amounts of
water near the surface. The big questions we are trying to answer are,
'where did all that water go?' and 'what are the implications for life?'
Measuring and mapping the icy soils in the polar regions of Mars as the
Odyssey team has done is an important piece of this puzzle, but we need
to continue searching, perhaps much deeper underground, for what happened
to the rest of the water we think Mars once had," said Jim Garvin, Mars
Program Scientist, NASA Headquarters, Washington.
Another new result from the neutron data is that large areas of Mars
at low to middle latitudes contain slightly enhanced amounts of hydrogen,
equivalent to several percent water by mass. Interpretation of this finding
is ongoing, but the team's preliminary hypothesis is that this relatively
small amount of hydrogen is more likely to be chemically bound to the minerals
in the soil, than to be in the form of water ice.
JPL manages the 2001 Mars Odyssey mission for NASA's Office of Space
Science, Washington. Investigators at Arizona State University, Tempe,
the University of Arizona, Tucson, and NASA's Johnson Space Center, Houston,
operate the science instruments. The gamma-ray spectrometer was provided
by the University of Arizona in collaboration with the Russian Aviation
and Space Agency, which provided the high-energy neutron detector, and
the Los Alamos National Laboratories, New Mexico, which provided the neutron
spectrometer. Lockheed Martin Astronautics, Denver, developed and built
the orbiter. Mission operations are conducted jointly from Lockheed Martin
and from JPL, a division of the California Institute of Technology in Pasadena.
Additional information about the 2001 Mars Odyssey and the gamma-ray
spectrometer is available on the Internet at: http://marsprogram.jpl.nasa.gov/odyssey/
and http://grs.lpl.arizona.edu
.
Mars
Mars
- "Russia
plans to put people on Mars." ... "Russian space
officials have announced an ambitious project to send people to Mars by
2015." ... "Leaders of the Russian space programme said the plan needed
international co-operation and they hoped to win support from both the
US National Aeronautics and Space Administration (Nasa) and the European
Space Agency (Esa)." -BBC
/News
- 
"Odyssey
Finds Water Ice in Abundance Under Mars' Surface."
-NASA.gov /Today
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Mars Odyssey Home Page." -NASA.gov
