Donald Savage
Headquarters, Washington
(Phone: 202/358-1547)

Mary Hardin
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/354-0344)

Heather Enos
University of Arizona, Tucson, Ariz.
(Phone: 520-621-8279)

RELEASE: 02-99

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://mars.jpl.nasa.gov/odyssey/ and
http://grs.lpl.arizona.edu.