The most dramatic findings so far from NASA’s twin Mars
rovers — telltale evidence for a wet and possibly habitable
environment in the arid planet’s past — passed rigorous
scientific scrutiny for publication in a major research journal.

Eleven reports by 122 authors in Friday’s issue of the
journal Science present results from Opportunity’s three-
month prime mission, fleshing out headline discoveries
revealed earlier.

Opportunity bounced to an airbag-cushioned landing on Jan.
24. It is exploring a region called Meridiani Planum, halfway
around Mars from where its twin, Spirit, landed three weeks
earlier. Sedimentary rocks Opportunity examined, “clearly
preserve a record of environmental conditions different from
any on Mars today,” report 50 rover-team scientists led by
Dr. Steve Squyres of Cornell University, Ithaca, N.Y. and Dr.
Ray Arvidson of Washington University, St. Louis, Mo.

“Liquid water was once intermittently present at the Martian
surface at Meridiani, and at times it saturated the
subsurface. Because liquid water is a key prerequisite for
life, we infer conditions at Meridiani may have been
habitable for some period of time in Martian history,”
according to Squires, Arvidson and other co-authors.

“Formal review and publication this week of these amazing
discoveries further strengthens the need for continued
exploration by orbiters, surface robots, sample-return
missions and human explorers. There are more exciting
discoveries awaiting us on the red planet,” said Dr. Michael
Meyer, chief scientist for Mars exploration at NASA
Headquarters, Washington.

Opportunity and Spirit have driven a combined 5.75 kilometers
(3.57 miles), nearly five times their mission-success goal.
They continue in good health after operating more than three
times as long as the three-month prime missions for which
they were designed.

NASA’s rover team makes the resulting scientific discoveries
available quickly to the public and the science community.
One type of evidence that Meridiani was wet is the
composition of rocks there.

The rocks have a high and variable ratio of bromine to
chlorine; indicating “the past presence of large amounts of
water,” write Dr. Rudi Rieder and Dr. Ralf Gellert of Max-
Planck-Institute for Chemistry, Mainz, Germany, and co-
authors. Their paper and another by Dr. Phil Christensen of
Arizona State University, Tempe, and collaborators report an
abundance of sulfur-rich minerals in the rocks, another clue
to a watery past. Clinching the case is identification of a
hydrated iron-sulfate salt called jarosite in the rocks, as
reported by Dr. Goestar Klingelhoefer of the University of
Mainz, and Dr. Richard Morris of NASA’s Johnson Space Center,
Houston, and co-authors.

Structures within the rocks add more evidence according to
Dr. Ken Herkenhoff of the U.S. Geological Survey, Flagstaff,
Ariz., and co-authors. Plentiful cavities, about the size of
shirt buttons, indicate crystals formed inside the rocks then
dissolved. Minerals carried by water formed peppercorn-size
gray spheres, nicknamed “blueberries,” that are embedded in
the rocks. Certain angled patterns of fine layers in some
rocks tell experts a flowing body of surface water shaped the
sediments that became the rocks.

Several characteristics of the rocks suggest water came and
went repeatedly, as it does in some shallow lakes in desert
environments on Earth. That fluctuation, plus the water’s
possible high acidity and saltiness, would have posed
challenges to life, but not necessarily insurmountable ones,
according to researchers. If life ever did exist at
Meridiani, the type of rocks found there could be good
preservers of fossils, according to Squyres, Dr. John
Grotzinger of the Massachusetts Institute of Technology,
Cambridge, and co-authors.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., has
managed the Mars Exploration Rover project since it began in
2000. Images and additional information about the rovers and
their discoveries are available on the Internet at:

http://www.nasa.gov/vision/universe/solarsystem/mer_main.html

Information about NASA and agency programs is available on
the Web at:

http://www.nasa.gov

Science Special Issue: Opportunity at Meridiani Planum 3 December 2004