Posted on behalf of Rick Lovett.
A meteorite that fell to Earth last July in Morocco has proven to be a rare chunk of Mars.
Only a handful of Martian meteorites are known, and only five (counting the new find) come from meteorites that were seen falling. That’s important because it tells scientists how long the meteorite has been lying on the ground, and, therefore, how much contamination it might have picked up. In this case, about a dozen pieces (such as the one shown, right), totalling several kilograms, were recovered from Morocco in late December.
“Because it’s only been on the ground for six months or less, it hasn’t been exposed to much contamination,” says Chris Herd, a planetary geologist specializing in meteorites at the University of Alberta in Edmonton, Canada. Herd is chairman of an international meteoritics committee that yesterday certified the rocks as coming from Mars and approved their name — Tissint — in honour of the village near which they were found.
The find is particularly important because it marks the first time a Martian meteorite has been collected from a witnessed fall since 1962 — when scientists were a lot less skilled than they are today in preventing contamination, Herd says.
The rocks were identified as martian by looking at their oxygen isotope ratios. “All Martian meteorites are offset in the composition of oxygen isotopes from rocks on the Earth and other places,” Herd explains. Further analysis will help scientists to trace the rocks, which are volcanic, back to the magmas that formed them. That in turn should help to reveal more about conditions in the Martian mantle.
Herd notes that the rocks may have been sitting on the Martian surface for hundreds of millions of years before they were blasted into space. “In that time, maybe water percolated through them,” he says. “We don’t know yet.”
And, he adds, “there’s an extremely outside chance that we might be able to find organic matter. Biological matter would be an extreme long shot, but again, because the rock is so fresh, there’s a bigger potential to look for those kinds of things and separate them from Earth contaminants.”
“This is an incredibly exciting find,” says Steve Squyres, a geologist at Cornell University in Ithaca, New York, who heads the science component of the current Mars rover explorations. “A lot of good science is going to come out of it.”
But igneous rocks aren’t the ideal choice for studies about the “big questions” regarding Mars, which are “climate, habitability, and life”, he adds. “The kinds of rocks that are most likely to preserve that kind of information are sedimentary rocks.”
Unfortunately, these aren’t the type of rocks most likely to survive the journey from Mars to Earth, because they’re relatively soft. “They fall apart easily,” he says. “And the process of hitting Mars with an asteroid, blasting rocks into space, and having them fall into the desert [on Earth] is fairly violent.”
This emphasizes the importance of a Mars sample-return mission, he says. “The Martian rocks we most seek we can’t expect nature to deliver to us,” he says. “We’re going to have to go and get them ourselves.”
Image: Department of Earth and Atmospheric Sciences, University of Alberta