A neutron spectrometer, designed and built at Los Alamos and flown aboard NASA's Mars Odyssey, has been mapping the Red planet for the past three months for hydrogen, an indicator of water-ice. This week Bill Feldman, Los Alamos' principal investigator for the neutron spectrometer, unveils data and detailed maps of the hydrogen-rich Martian terrain at the American Geophysical Union conference in Washington D.C.
The results also appear in the May 31 issue of Science magazine.
"The surface soils of Mars are rich in hydrogen," said Feldman. "Soil extending 60 degrees from the Martian poles contain from 35 percent to 100 percent of water-ice buried beneath a shallow overburden of hydrogen-poor soil. Although scientists have known that water ice is stable close to the surface in these regions, our new measurements are the first to give the amount of near-surface water on Mars.
"The amount of water present on Mars is sufficiently large that it can support future human exploration activities," Feldman continued. "We have anticipated these results for 17 years and are excited that all of our wishes and hard work have been fulfilled."
The neutron spectrometer maps show that the large region that extends from the poles to within about 50 degrees of the equator contains Mars' most abundant reservoirs of hydrogen, or water ice. The large expanses at low to middle latitudes of Mars also contain significant amounts of hydrogen, which are most likely deposits of chemically and/or physically bound water and/or hydroxyl radicals – one hydrogen atom bound to one oxygen atom.
The neutron spectrometer data are supported by simultaneous measurements made using Mars Odyssey's gamma-ray spectrometer, operated by the University of Arizona.
Los Alamos' neutron spectrometer began mapping the Martian surface while it was summer in the south and winter in the north. It revealed the extent to which the northern and southern polar caps are covered in a thick layer of carbon dioxide, or dry ice. During winter, the carbon dioxide layers extend from the poles to within about 60 degrees of the equator because the dry ice frost settles out of the atmosphere when temperatures fall about 186 degrees below zero Fahrenheit. During the warmer summer the carbon dioxide layer evaporates completely in the north but remains as a thick cover of the residual polar cap in the south.
The first successful attempt to measure the global distribution of neutrons about a planetary body was made using a similar neutron spectrometer aboard Lunar Prospector. Comparisons between the lunar and Martian neutron spectrometer data reveal that Mars' soil is richer in hydrogen than is the moon's soil by more than several factors of 10 to several factors of 1,000.
Los Alamos neutron spectrometer will continue to measure neutrons that leak outward from the upper meter of the Martian soil for several more years. Mars Odyssey's orbit is such that the entire planet's surface is sampled in four-degree longitudinal increments weekly.
Scientists will use these data not only to determine the amount of water on Mars, but to map the basaltic lava cover, measure the seasonal variation of dry-ice frost that covers both poles during their winter months and help interpret data from the gamma-ray spectrometer to determine the quantity and composition of the most abundant elements on the planet.
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EDITORS' NOTE: Photographs for news use are available at: http://www.lanl.gov/orgs/pa/News/MarsOdyssey.html online.
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Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health, and global security concerns.