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.
6-26-98 DEA
#9867