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Contact: Jim Danneskiold
jdanneskiold{at}lanl.gov
505-667-1640
DOE/Los Alamos National Laboratory

Los Alamos makes first map of ice on Mars
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February 15, 2003

DENVER, COLO. -- Lurking just beneath the surface of Mars is enough 
water to cover the entire planet ankle-deep, says Los Alamos National
Laboratory scientist Bill Feldman.

Feldman on Saturday released the first global map of hydrogen 
distribution identified by instruments aboard NASA's Mars Odyssey 
spacecraft and offered initial minimum estimates of the total amount 
of water stored near the Martian surface. His presentation came at the 
annual meeting of the American Association for the Advancement of 
Science in Denver.

For nearly a year, Los Alamos' neutron spectrometer has been carefully
mapping the hydrogen content of the planet's surface by measuring 
changes in neutrons given off by soil, an indicator of hydrogen likely 
in the form of water-ice, within about 35 degrees latitude of the 
north and south poles. A color map is available at
http://www.lanl.gov/worldview/news/pdf/MarsWater.pdf online.

"It's becoming increasingly clear that Mars has enough water to 
support future human exploration," Feldman said. "In fact, there's 
enough to cover the entire planet to a depth of at least five inches, 
and we've only analyzed the top few feet of soil."

The new map is based on views of the red planet through more than half 
a Martian year of 687 Earth days, so researchers have been able to see 
both poles without obstruction by the seasonal polar caps of frozen 
carbon dioxide, dry ice. From about 55 degrees latitude to the poles, 
Mars has extensive deposits of soils that are rich in water-ice, 
bearing an average of 50 percent water by mass. In other words, 
Feldman said, a typical pound of soil scooped up in those polar 
regions would yield an average of half a pound of water if it were 
baked in an oven.

The tell-tale traces of hydrogen, and therefore the presence of 
hydrated minerals, also are found in lower concentrations closer to 
Mars' equator, ranging from two- to 10-percent water by mass. 
Surprisingly, two large areas, one within Arabia Terra, the 
1,900-mile-wide Martian desert, and another on the opposite side of 
the planet, show indications of relatively large concentrations of 
sub-surface hydrogen.

"The big reason we're so confident now is that we have an absolute
calibration of our results," Feldman said. He and his Los Alamos 
colleagues recently compared their neutron spectrometer readings as 
Odyssey flew over the north pole during early spring, when the dry-ice 
ground cover was thickest, against simulations of the spectrometer's 
response to a thick layer of pure dry ice. This allowed them to 
calibrate the Odyssey readings with a known Martian soil type.

"We're sure there's dry-ice precipitation at the poles because the
temperature of the ground cover is within the range for dry ice. And 
we can tell how thick the icecaps are, from the measured intensity of 
hydrogen gamma rays coming from underneath the icecaps," Feldman said. 
"We went from thick dry ice to a low-hydrogen abundance calibration 
when we applied our 'neutron ruler' at Mars' equatorial latitudes. We 
were surprised to see such huge amounts of hydrogen at those lower 
latitudes: close to 10 percent in some places."

How did water vapor get into the subsurface soils and into rocks 
farther beneath the surface of Mars? The effort to answer that 
question and to reconstruct the Martian hydrologic cycle will occupy 
Feldman and his colleagues for years to come.

Hydrogen is only absorbed chemically near rock surfaces, but Mars 
geology appears to be rich in minerals as zeolites, clays and 
magnesium sulfate, all of which can retain significant amounts of 
water.

"This is material that has absorbed the hydrogen chemically and has 
retained it for millions of years," Feldman explained.

The team also studied meteor craters more than 250 miles across such 
as Schiaparelli and discovered that the water content in the crater's 
center is reduced.

Scientists are attracted to two possible theories of how all that 
water got into the Martian soils and rocks.

The vast water icecaps at the poles may be the source. The thickness 
of the icecaps themselves may be enough to bottle up geothermal heat 
from below, increasing the temperature at the bottom and melting the 
bottom layer of the icecaps, which then could feed a global water 
table.

On the other hand, there is evidence that about a million years or so 
ago, Mars' axis was tilted about 35 degrees, which might have caused 
the polar icecaps to evaporate and briefly create enough water in the 
atmosphere to make ice stable planet-wide. The resultant thick layer 
of frost may then have combined chemically with hydrogen-hungry soils 
and rocks.

"We're not ready yet to precisely describe the abundance and 
stratigraphy of these deposits at high latitudes, but the neutron 
spectrometer shows water ice close to the surface in many locations, 
and buried elsewhere beneath several inches of dry soils," Feldman 
said. "Some theories predict these deposits may extend a half mile or 
more beneath the surface; if so, their total water content may be 
sufficient to account for the missing water budget of Mars."

In fact, a team of Los Alamos scientists has begun a research project 
to interpret the Mars Odyssey data and their ramifications for the 
history of Mars' climate. The project is funded through the Laboratory 
Directed Research and Development program -- which funds innovative 
science with a portion of the Laboratory's operating budget -- and 
seeks to develop a global Martian hydrology model, using vast amounts 
of remote sensing data, topography maps and experimental results on 
water loading of minerals.

Researchers working with Feldman on the Odyssey project include Tom
Prettyman, Bob Tokar, Kurt Moore, Herb Funsten, David Lawrence and 
Richard Elphic.

Los Alamos' neutron spectrometer, a more sensitive version of the 
instrument that found water ice on the moon five years ago, is one 
component of the gamma-ray spectrometer suite of instruments aboard 
Odyssey. Prof. William V.  Boynton of the University of Arizona leads 
the gamma-ray spectrometer team.

The neutron spectrometer looks for neutrons generated when cosmic rays 
slam into the nuclei of atoms on the planet's surface, ejecting 
neutrons skyward with enough energy to reach the Odyssey spacecraft 
250 miles above the surface. Elements create their own unique 
distribution of neutron energy -- fast, thermal or epithermal -- and 
these neutron flux signatures indicate what elements make up the soil 
and how they are distributed. Thermal neutrons are low-energy neutrons 
in thermal contact with the soil; epithermal neutrons are 
intermediate, scattering down in energy after bouncing off soil 
material; and fast neutrons are the highest-energy neutrons produced 
in the interaction between high-energy galactic cosmic rays and the 
soil.

By looking for a decrease in epithermal neutron flux, researchers can 
locate hydrogen. Hydrogen in the soil efficiently absorbs the energy 
from neutrons, reducing their flux in the surface and also the flux 
that escapes the surface to space where it is detected by the 
spectrometer. Since hydrogen is likely in the form of water-ice at 
high latitudes, the spectrometer can measure directly, a yard or so 
deep into the Martian surface, the amount of ice and how it changes 
with the seasons.

Mars Odyssey was launched from Cape Canaveral Air Force Station in 
April 2001 and arrived in Martian orbit in late October 2001. During 
the rest of the spacecraft's 917-day science mission, Los Alamos' 
neutron spectrometer will continue to improve the hydrogen map and 
solve more Martian moisture mysteries.

Jet Propulsion Laboratory, a division of the California Institute of
Technology in Pasadena, manages the Mars Odyssey mission for NASA's 
Office of Space Science in Washington, D.C. Investigators at Arizona 
State University in Tempe, the University of Arizona in Tucson and 
NASA's Johnson Space Center, Houston, operate the science instruments. 
Additional science partners are located at the Russian Aviation and 
Space Agency and at Los Alamos National Laboratories, New Mexico. 
Lockheed Martin Astronautics, Denver, the prime contractor for the 
project, developed and built the orbiter. Mission operations are 
conducted jointly from Lockheed Martin and from JPL.

                                     ###

Los Alamos National Laboratory is operated by the University of 
California for the National Nuclear Security Administration (NNSA) of 
the U.S.  Department of Energy and works in partnership with NNSA's 
Sandia and Lawrence Livermore national laboratories to support NNSA in 
its mission.

Los Alamos enhances global security by ensuring safety and confidence 
in the U.S. nuclear stockpile, developing technologies to reduce 
threats from weapons of mass destruction and improving the 
environmental and nuclear materials legacy of the cold war. Los 
Alamos' capabilities assist the nation in addressing energy, 
environment, infrastructure and biological security problems

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