[meteorite-list] Matching Mars to Meteorites

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:14 2004
Message-ID: <200404161625.JAA28892_at_zagami.jpl.nasa.gov>

http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=924

Matching Mars to Meteorites
By Leslie Mullen
Astrobiology Magazine
April 16, 2004

NASA reported Wednesday that a rock on
Mars seems to be very similar in composition to
a meteorite that once fell to Earth.

The meteorite, discovered in Antarctica in 1979
and labeled EETA79001-B, was known to be
from Mars because of gases preserved in glassy
material in the rock. These gases matched the
atmospheric composition of Mars measured by
the Viking mission.

EETA79001 was launched into space from Mars
600,000 years ago, after an asteroid impact
tossed it high enough to escape Martian gravity.
The meteor is actually composed of two rocks
fused together, the "A" and "B" portions. The
"A" portion of the meteorite does not match the
mineralogy of the rock analyzed on Mars.

The Mars rock that is similar to EETA79001-B
is "Bounce" rock, the rock that the airbagged
rover struck while it rolled to a stop.
Opportunity used its Rock Abrasion Tool to
grind away at the surface of Bounce rock, and
the spectral signature of the underlying layer
shows a composition of 69 percent pyroxene, 20
percent plagioclase, and 11 percent olivine.

This mineral composition differs from the
Meridiani Plains where the rock is situated, so
scientists think it must have come from elsewhere.
And unlike the Meridiani Plains, Bounce rock is
completely lacking in hematite.

Bounce rock is also different from the basalt
that dominates the geology of Mars. Basalt has
much more plagioclase and less pyroxene than
Bounce rock has.

"The Gusev rocks that they're measuring with
Spirit are very similar to the global basalts,
but this rock is very different," says Deanne
Rogers of Arizona State University.

Because Bounce rock is lying on the surface, it
is likely part of the impact debris that
emanates outwards from a nearby crater. Dr.
Benton Clark of Lockheed Martin Corporation
says it probably was deposited in its current
position long after water was on the surface of Mars.

"What we have thought all along is that the aqueous period in
that area is fairly old, dating back to the earlier times on Mars,
and so this may be additional evidence relevant to that," says
Clark.

There are some spectral differences between Bounce rock and
EETA79001-B, largely due to differences in the type and
abundance of pyroxene. This indicates the two rocks didn't
come from the same impact event, but perhaps had similar
formation conditions or came from similar source regions.

Over 22,000 meteorites have been collected on Earth, but only
30 are of Martian origin. The science team compared Bounce
rock to the Shergotty Mars meteorite, which was found in India
in 1865. Shergotty had some mineral similarities to Bounce rock,
but was not as close a match as EETA79001-B.

In addition to the analysis of Bounce rock, the science team
reported that Spirit and Opportunity paused in their exertions to
receive new software updates. Spirit will now continue its drive
to Columbia Hills, and because the new software enhances the
rovers' mobility it should allow Spirit to drive much further each
sol. Opportunity has dug a trench at the Anatolia fracture site,
and it will now continue its work on the trench and then
afterwards continue its drive to the Endurance crater.

The new software also added a deep-sleep mode to the rovers,
and this should resolve the heater that is stuck in the "on"
position on the Opportunity rover. In addition, the software
should mitigate the memory problem Spirit had on sol 18.

Spirit and Opportunity have now sent about 24,000 images of
Mars back to Earth. The Lion King panorama is a mosaic
composed of 600 images and 6 different filters. The panorama
shows Eagle crater, the lander, and the tracks made by the
Opportunity rover as it investigated the crater and then finally
drove out onto the Meridiani Plain.

"It's a wonderful recap of the mission thus far," says Jason
Soderblom of Cornell University.
Received on Fri 16 Apr 2004 12:25:30 PM PDT