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Mars
Rover Finds Rock Resembling
Meteorites That Fell to Earth
NASA's Opportunity rover has examined an odd volcanic rock on the
plains of Mars' Meridiani Planum region with a composition unlike
anything seen on Mars before, but scientists have found similarities
to meteorites that fell to Earth.
"We think we have
a rock similar to something found on Earth," said Dr. Benton
Clark of Lockheed Martin Space Systems, Denver, science-team member
for the Opportunity and Spirit rovers on Mars. The similarity seen
in data from Opportunity's alpha particle X-ray spectrometer "gives
us a way of understanding 'Bounce Rock' better," he said. Bounce
Rock is the name given to the odd, football-sized rock because Opportunity
struck it while bouncing to a stop inside protective airbags on landing
day.
The resemblance helps resolve a paradox about the meteorites, too.
Bubbles of gas trapped in them match the recipe of martian atmosphere
so closely that scientists have been confident for years that these
rocks originated from Mars. But examination of rocks on Mars with
orbiters and surface missions had never found anything like them,
until now.
"There is a striking similarity in spectra,"
said Christian Schroeder, a rover science-team collaborator from the
University of Mainz, Germany, which supplied both Mars rovers' Moessbauer
spectrometer instruments for identifying iron-bearing minerals.
Mars Exploration Rover scientists described two such meteorites in
particular during a Mars Exploration Rover news conference at NASA's
Jet Propulsion Laboratory, Pasadena, Calif. One rock, named Shergotty,
was found in India in 1865 and it gave its name to a class of meteorites
called shergottites. A shergottite named EETA79001 was found in Antarctica
in 1979 and has an elemental composition even closer to Bounce Rock's.
Those two and nearly 30 other meteorites found on Earth are believed
to have been ejected from Mars by the impacts of large asteroids or
comets hitting Mars.
Opportunity's miniature thermal emission spectrometer indicates that
the main ingredient in Bounce Rock is a volcanic mineral called pyroxene,
said science-team collaborator Deanne Rogers of Arizona State University,
Tempe. The Moessbauer spectrometer also identified pyroxene in the
rock. The high proportion of pyroxene makes it unlike not only any
other rock studied by Opportunity or Spirit, but also unlike the volcanic
deposits mapped extensively around Mars by a similar spectrometer
on NASA's Mars Global Surveyor orbiter, Rogers said.
Thermal infrared imaging by another orbiter, Mars Odyssey, suggests
a possible origin for Bounce Rock. An impact crater about 25 kilometers
wide (16 miles wide) lies about 50 kilometers (31 miles) southwest
of Opportunity. The images show that some rocks thrown outward by
the impact that formed that crater flew as far as the distance to
the rover. "Some of us think Bounce Rock could have been ejected
from this crater," Rogers said.
Opportunity is driving eastward, toward a crater dubbed "Endurance"
that might offer access to thicker exposures of bedrock than the rover
has been able to examine so far. With new software to improve mobility
performance, the rover may reach Endurance within two weeks, said
JPL's Jan Chodas, flight software manager for both Mars Exploration
Rovers.
Mission controllers at JPL successfully sent new versions of flight
software to both rovers.
A parting look at the small crater in which Opportunity landed is
part of a full 360-degree color panorama released at the news conference.
The view combines about 600 individual frames from the rover's panoramic
camera, said science-team collaborator Jason Soderblom of Cornell
University, Ithaca, N.Y. It is called the Lion King panorama because
it was taken from a high-ground viewpoint at the edge of the crater,
like the high-ground viewpoint used by animal characters in the Lion
King story.
The panorama gives a good sense of how wind has uncovered the outcrop
at the upwind side of the crater and deposited sand in the downwind
side of the crater and bright martian dust in the wind shadow of the
crater, Soderblom commented. On the wide plain outside the crater
lies Bounce Rock.
JPL, a division of the California Institute of Technology in Pasadena,
manages the Mars Exploration Rover project for NASA's Office of Space
Science, Washington, D.C. Images and additional information about
the project are available from JPL athttp://marsrovers.jpl.nasa.gov
and from Cornell University, Ithaca, N.Y., athttp://athena.cornell.edu.
© CONTACTO Magazine
Published on April 29, 2004
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