Matching Mars to Meteorites
|Opportunity bounced off this rock called "Bounce", the only rock in sight, and landed abruptly in Eagle Crater. The rock abrasion tool has left it drill marks on the rock.|
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.
|Major investigated regions of Antarctica where meteors have been successfully identified. At any given moment, the interplanetary sample transit works out to about one Martian meteorite landing on Earth each month. Scientists had thought it took a serious wallop to instigate these interplanetary exchanges. Impacts of this size and larger occur every 200,000 years or so on Mars. Yet research now finds that craters as small as 1.9 miles (3 kilometers) wide on Mars could have been the starting points for meteorite launches towards Earth. |
Credit: JSC/NASA Meteor Program
"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.
|This meteorite, EETA79001, a basalt lava rock nearly indistinguishable from many Earth rocks, provided the first strong proof that meteorites could come from Mars. Originally weighing nearly 8 kilograms (17.6 pounds), it was collected in 1979 in the Elephant Moraine area of Antarctica. |
Credit:NASA/JSC/JPL/Lunar Planetary Institute
Spirit and Opportunity have now sent about 24,000 images of Mars back to Earth. The Lion King panorama (banner) 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.