Mars salt deposit discovery points to a new place to hunt for life's ancient traces

TEMPE, Ariz. – Scientists using a Mars-orbiting camera designed and operated at Arizona State University's Mars Space Flight Facility have discovered the first evidence for deposits of chloride minerals - salts - in numerous places on Mars. These deposits, say the scientists, show where water was once abundant and may also provide evidence for the existence of former Martian life.

A team of scientists led by Mikki Osterloo, of the University of Hawaii, used data from the Thermal Emission Imaging System (THEMIS) on NASA's Mars Odyssey orbiter to discover and map the Martian chloride deposits. The Jet Propulsion Laboratory in Pasadena, Calif., manages the Mars Odyssey mission for NASA's Science Mission Directorate.

Developed at Arizona State University, THEMIS is a multi-wavelength camera that takes images in five visual bands and 10 infrared ones. At infrared wavelengths, the smallest details THEMIS can see on the Martian surface are 330 feet (100 meters) wide.

The scientists found about 200 individual places in the Martian southern hemisphere that show spectral characteristics consistent with chloride minerals. These salt deposits occur in the middle to low latitudes all around the planet within ancient, heavily cratered terrain. The team's report appears in the March 21, 2008 issue of the scientific journal Science.

The team includes Philip Christensen, Joshua Bandfield, and Alice Baldridge of Arizona State University; Victoria Hamilton and Scott Anderson of the University of Hawaii; Timothy Glotch of Stony Brook University; and Livio Tornabene of the University of Arizona.

Lead author Osterloo found the sites by looking through thousands of THEMIS images processed to reveal, in false colors, compositional differences on the Martian surface. As she explains, "I started noting these sites because they showed up bright blue in one set of images, green in a second set, and yellow-orange in a third."

Says team member Christensen, "THEMIS gives us a good look at the thermal infrared, the best part of the spectrum for identifying salt minerals by remote sensing from orbit."

When plotted on a global map of Mars, the chloride sites appeared only in the southern highlands, the most ancient rocks on Mars.

Lay of the Land

Christensen goes on to characterize the sites' geological setting. "Many of the deposits lie in basins with channels leading into them," he says. "This is the kind of feature, like salt-pan deposits on Earth, that's consistent with water flowing in over a long time."

Christensen, a Regents' Professor of Geological Sciences at ASU's School of Earth and Space Exploration in the College of Liberal Arts and Sciences, designed THEMIS and is the instrument's principal investigator.