Impact Crater Origin of Mars Meteorites Discovered

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Out of the thousands of craters scarring the face of Mars, one has emerged as the likely source of most of the Martian meteorites that have been recovered on Earth, a new study shows.

A piece of rock found its way all the way from Mars to a desert in northwest Africa. And now it has the potential to tell us all kinds of things about the Red Planet.

Researchers pinpoint Mojave Crater, a 34 mile (55 kilometer) wide basin on the planet’s equator, as the origin of the so-called “shergottites” meteorites, a family that includes about 75 percent of the roughly 150 known Martian meteorites.

The crater is located slightly north and east of Meridian Planum, where NASA’s Mars rover Opportunity landed in January 2004.

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Knowing where the meteorites came from would help scientists piecing together the history and evolution of Mars, the planet most like Earth in the solar system.

With clear evidence of past surface water, Mars remains a prime candidate in the search for life beyond Earth.

Researchers homed in on Mojave Crater as the source of the shergottites for several reasons. First, its large size means it was created by an impact powerful enough to launch debris into space. Based on the amount of cosmic ray exposure the meteorites experience in space, scientists estimate the rocks spent 5 million years in interplanetary space before reaching Earth.

The shergottites that have cosmic ray exposures of only about 1 million years broke apart during transit, exposing fresh surfaces and new interiors to radiation, planetary scientist Stephanie Werner, with the University of Oslo in Norway, theorizes in a paper published in this week’s Science.

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Second, Mojave Crater is relatively young, formed from an impact that took place less than 5 million years ago on terrain that is roughly 4.3 billion years old. That's the same age, the researchers say, as when the shergottites originally crystallized.

The third and final piece of evidence comes from a chemical analysis of the crater made from data collected by instruments aboard Europe’s Mars Express and NASA’s Mars Reconnaissance Orbiter satellites. Scientists found telltale chemical fingerprints of pyroxene and olivine in and around the crater, two minerals commonly present in the Martian meteorites.

“Only Mojave Crater combines the appropriate site mineralogy, size, and the young crater-formation age of less than 5 million years,” Werner wrote in an email to Discovery News.

“Additionally, the shergottite meteorites are igneous rocks which have formed at the depth of up to a few kilometers, thus most volcanic provinces can be excluded,” Werner added.

Not everyone agrees with the scientists’ conclusions.

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“The lines of evidence that they use are not widely accepted,” Carl Agee, director of University of New Mexico’s Institute of Meteoritics, told Discovery News.

Agee points to the age of shergottites, which Werner and colleagues claim are old.

“Most scientists who have studied the meteorites and done age-dating … have data that shows they are quite young, geologically speaking,” Agee said.

“That’s the heart of this story and that, in itself , already is a controversial position to take,” he said.

Combined with arguments about the chemical composition of the crater, among other factors, to conclude that it is a match “strikes me as somewhat speculative,” Agee said.

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