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Water History, Rock Composition Among Latest Findings A Year After Mars

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov

Contact: Diane Ainsworth

FOR IMMEDIATE RELEASE                            June 29, 1998

WATER HISTORY, ROCK COMPOSITION AMONG LATEST FINDINGS A YEAR AFTER MARS
PATHFINDER

       A year after the landing of Mars Pathfinder, mission scientists say
that data from the spacecraft paint two strikingly different pictures of the
role of water on the red planet, and yield surprising conclusions about the
composition of rocks at the landing site.

       "Many of the things that we said last summer during the excitement
after the landing have held up well," said Dr. Matthew Golombek, Pathfinder
project scientist at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA.
"But we have now had more time to study the data and are coming up with some
new conclusions."

       Similar to on-going science results from NASA's Mars Global Surveyor
spacecraft currently in orbit around Mars, Pathfinder data suggest that the
planet may have been awash in water three billion to 4.5 billion years ago.
The immediate vicinity of the Pathfinder landing site, however, appears to
have been dry and unchanged for the past two billion years.

       Several clues from Pathfinder data point to a wet and warm early
history on Mars, according to Golombek. Magnetized dust particles and the
possible presence of rocks that are conglomerates of smaller rocks, pebbles
and soil suggest copious water in the distant past. In addition, the bulk of
the landing site appears to have been deposited by large volumes of water,
and the hills on the horizon known as Twin Peaks appear to be streamlined
islands shaped by water.

       But Pathfinder images also suggest that the landing site is
essentially unchanged since catastrophic flooding sent rocks tumbling across
the plain two billion years ago. "Since then this locale has been dry and
static," he said.

       While the area appears to have been untouched by water for eons, wind
appears to have been steadily eroding rocks at the landing site. Analysis of
Pathfinder images shows that about about three to five centimeters (one to
two inches) of material has been stripped away from the surface by wind,
Golombek noted.

       "Overall, this site has experienced a net erosion in recent times,"
said Golombek. "There are other places on Mars that are net 'sinks,' or
places where dust ends up being deposited. Amazonis Planitia, for example,
probably has about one to two meters (three to six feet) of fine, powdery
dust that you would sink into if you stepped on it."

       Chemical analysis of a number of rocks by the alpha proton X-ray
spectrometer (APXS) instrument on Pathfinder's mobile Sojourner rover,
meanwhile, reveals an unexpected composition that scientists are still
trying to explain.

       The current assessment of data from this instrument suggests that all
of the rocks studied by the rover resemble a type of volcanic rock with a
high silicon content known on Earth as andesite, covered with a fine layer
of dust. All of the rocks appear to be chemically far different from
meteorites discovered on Earth that are believed to have come from Mars.

       "The APXS tells us that all of these rocks are the same thing with
different amounts of dust on them," said Golombek. "But images suggest that
there are different types of rocks. We don't yet know how to reconcile
this."

       When molten magma oozes up from a planet's mantle onto the surface of
the outer crust, it usually freezes into igneous rock of a type that
geologists call a basalt. This is typical on the floors of Earth's oceans,
as well as on the maria of the Moon and in many regions of Mercury and
Venus. By contrast, andesites typically form on Earth in tectonically active
regions when magma rises into pockets within the crust, where some of its
iron and magnesium-rich components are removed, leaving rock with a higher
silicon content. "We don't believe that Mars has had plate tectonics, so
these andesites must have formed by a different mechanism," Golombek said.

       The rocks studied by Pathfinder most closely resemble andesites found
in Iceland and the Galapagos Islands, tectonic spreading centers where
plates are being pushed apart, said Dr. Joy Crisp, an investigation
scientist on the spectrometer experiment at JPL. Andesites from these areas
have a different chemical signature from andesites formed at subduction
zones, mostly because wet ocean sediments carry more water down into the
mantle at the subduction zones. "On Mars, where the water content is
probably lower and there is no evidence of subduction, we would expect a
closer chemical similarity to Iceland andesites," said Crisp.

       The Martian rocks may have other origins, however. They could be
sedimentary and influenced by water processes; they could be formed by
melting processes resulting from a meteor impact; or, a third alternative is
that the rocks might be basaltic, but covered by a silicon-rich weathering
coating. "In any event, the presence of andesites on Mars is a surprise, if
it is borne out as we study the data further," said Crisp. "Most rocks on
Mars are expected to be basalts lower in silicon. If these are in fact
andesites, they are probably not very abundant."

       Pathfinder scientists are looking forward to more data from the
Thermal Emission Spectrometer instrument on the Mars Global Surveyor to
reveal more about the chemical composition of the planet's surface,
especially once the orbiting spacecraft begins its prime circular mapping
mission in spring 1999.

       In other recent Pathfinder science findings, Dr. Steven Metzger of
the University of Nevada found direct evidence of gusting winds called "dust
devils" in images from Pathfinder's lander. Such dust devils had been seen
in some Viking orbiter images and inferred from measurements of atmospheric
pressure and winds by other instruments on the Pathfinder lander, but were
not spotted in actual surface images until Metzger's discovery.

       JPL planetary scientist Dr. Diana Blaney has been using data from
Pathfinder, other spacecraft missions and ground-based observations to study
weathering on Mars. Her work suggests that Mars is uniformly covered by a
fine coating of dust formed by an unusual process involving meteor impacts
and volcanic gases that add sulfur.

       NASA's next Mars missions, the 1998 Mars Climate Orbiter and Mars
Polar Lander, are in testing now for launch in December and January,
respectively. Whereas Pathfinder's science focus was on exploring rocks with
its mobile robotic geologist, the Mars Polar Lander will focus on a search
for water under the planet's surface, equipped with a robot arm that will
dig into the soil at the landing site near the planet's south pole.

       Launched on December 4, 1996, Pathfinder reached Mars on July 4,
1997, directly entering the planet's atmosphere and bouncing on inflated
airbags as a technology demonstration of a new way to deliver a lander and
rover to Mars. The lander operated nearly three times its design lifetime of
30 days, while the rover operated 12 times its design lifetime of seven
days.

       During the mission, the spacecraft relayed an unprecedented 2.3
gigabits of data, including 16,500 images from the lander's camera, 550
images from the rover camera, 16 chemical analyses of rocks and soil, and
8.5 million measurements of atmospheric pressure, temperature and wind.

       Mars Pathfinder was designed, built and operated by JPL for NASA's
Office of Space Science, Washington, DC. JPL is a division of the California
Institute of Technology, Pasadena, CA.

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