Thursday, March 13, 2014

Martian Meteorites Source Found?

Martian meteorite
The Los Angeles meteorite, found in California's Mojave Desert, has proven to be a chunk of Mars known as a shergottite. The scale cube is 1 cm on a side.
Copyright 2000 Ron Baalke.

Where did the Martian meteorites called shergottites come from? A team of European researchers believe their launch pad was a fresh-looking 58-km-wide crater punched into ancient terrain less than 5 million years ago.

Imagine walking into a room full of geologists, plunking a box full of rocks on a table, and asking them to figure out where on Earth your samples came from.

That's the challenge facing the researchers who study meteorites from the planet Mars. The count of Martian stones now totals about 150, representing 69 discrete falls on Earth. All igneous rocks, they fall into three compositional clans known as shergottites, nakhlites, and chassignites — named for an archetype within each group. (There's one oddball, an ancient rock known as ALH 84001, that has gotten a lot of attention in past years.)

The rocks themselves are old. However, they were blasted from the Martian surface in the geologically recent past, based on how long they were exposed to cosmic rays in space before reaching Earth: 11 million years ago for the nakhlites and chassignites, and just 1 to 5 million years ago for the shergottites.

So where'd they come from? That question has dogged planetary geologists for decades. But they've now got powerful new tools — three heavily instrumented orbiters around Mars — to try to identify the interplanetary launch pads. Several researchers have suggested young-looking Martian craters as possibilities in the past.

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Source: Sky and Telescope Magazine.

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