By Cheryl Pellerin
USINFO Staff Writer

This is the first article in a two-part series on the international exploration of Mars.

Washington – After a long and heartbreaking history of failed attempts by several nations to reach and explore the fourth planet from the sun, a range of instruments on or orbiting Mars is helping international scientists understand the Red Planet’s composition and structure and the history and fate of its water supply.

These mechanized planetary explorers include NASA’s long-lived robotic rovers Spirit and Opportunity; NASA’s Mars Odyssey orbiter, whose global observations target the planet’s climate and geologic history; and the European Space Agency's (ESA) Mars Express spacecraft, which carries a radar instrument built by NASA and Agenzia Spaziale Italiana (ASI), the Italian space agency.

Mars Express, launched in 2003, is the first non-U.S. mission to reach Mars.

“Last week, we completed the 38th Lunar and Planetary Science Conference in Houston,” said David Beaty, chief scientist for the Mars Program at NASA’s Jet Propulsion Laboratory (JPL) in California, in a March 20 USINFO interview, “and the Mars exploration program is showing outstanding progress.”

Three missions now at Mars have completed their planned primary objectives and are in extended mission phases. “All three keep generating new discoveries,” he said.

Another mission, NASA’s Mars Reconnaissance Orbiter, launched in 2005 to search for evidence that water persisted on the Mars’ surface for a long period of time, “entered its primary mapping phase four months ago and has been returning spectacular data,” Beaty said. “These results dominated the conference.”

Less than a year after the orbiter arrived at Mars and four months since its science phase began, instruments aboard the spacecraft are making good on the promise to advance fundamental knowledge of the planet.

ROVER EXPLORATIONS

While driving toward the side of a Martian mound called McCool Hill, the wheels of NASA's Mars Exploration Rover Spirit churned up the largest amount of bright soil discovered so far in a mission that now has lasted more than three years – far surpassing the 90 days originally planned.

"This material could have been left behind by water that dissolved these minerals underground, then came to the surface and evaporated,” said Ray Arvidson of Washington University in Missouri, deputy principal investigator for NASA's twin rovers, Spirit and Opportunity, “or it could be a volcanic deposit formed around ancient gas vents."

Determining which theory is correct will strengthen understanding of the environmental history of the Columbia Hills region that Spirit has been exploring since a few months after landing in 2004. But investigating the soil is a challenge for the rover team because loose material could trap the rover.

The bright white and yellow material was hidden under a layer of normal-looking soil until Spirit's wheels churned it up while struggling to cross a patch of unexpectedly soft soil nearly a year ago.

Spirit measured the material’s composition and mineralogy and found that it is sulfur-rich and consists of sulfate salts associated with iron, and probably calcium. Researchers will watch for more patches of the soil.

On the other side of Mars, Opportunity is exploring the edges of Victoria Crater, a bowl about 800 meters across. Cliff-like promontories alternate with more gradually sloped alcoves around the scalloped rim. The impact that dug the crater exposed previously buried layers.

WATER ON MARS

Understanding the history and fate of water on Mars is critical to determining whether Mars ever has supported life, because all known life depends on liquid water.

That job is among the tasks assigned to the Mars advanced radar for subsurface and ionospheric sounding (MARSIS), whose new measurements of Mars' southern polar region indicate extensive frozen water. MARSIS also is mapping the thickness of similar layered deposits at the northern polar region.

"The amount of water [the south polar layered deposits] contain has been estimated before, but never with the level of confidence this radar makes possible," said Jeffrey Plaut of JPL and co-principal investigator for the radar, in a March 15 statement.

NASA and ASI jointly developed the MARSIS instrument, which is aboard the Mars Express orbiter. The instrument was developed under the scientific supervision of the University of Rome "La Sapienza" in partnership with JPL and the University of Iowa.

The polar region contains enough frozen water to cover the planet in a liquid layer about 11 meters deep. The new estimate comes from mapping the ice’s thickness.

The Mars Express orbiter's radar instrument has made more than 300 virtual slices through layered deposits covering the pole to map the ice. The radar sees through icy layers to the lower boundary, which is as deep as 3.7 kilometers below the surface. Detecting the shape of the ground surface beneath the ice deposits provides information about even deeper structures of Mars.

Polar layered deposits hold most of the known water on Mars, though other areas of the planet seem to have been very wet at times in the past.

More information about NASA’s Mars exploration program is available on the agency’s Web site.

For additional information on U.S. support for space exploration, see Science and Technology.