Scientists probe fresh Martian meteorite 

Rock holds clues to Red Planet’s atmosphere and surface conditions

A meteorite that streaked to Earth in a blazing fireball over the Moroccan desert is one of the freshest samples of the Red Planet’s surface and atmosphere that scientists have ever seen.

MARTIAN METEORITE This 1.1-kilogram chunk of the Tissint Martian meteorite shows distinct charring from Earth’s atmosphere and pockets of black glass that contain trapped gas from Mars. Natural History Museum, London

Desert nomads recovered fragments of the Tissint meteorite, one of just five from Mars that have been seen during their descent, after it landed early in the morning of July 18, 2011. The space rock resembles a meteorite found in Antarctica in 1980 that was the first to show strong evidence of its Martian origin. But unlike other Martian meteorites that have sat on Earth’s surface for tens or hundreds of years before being discovered, Tissint hasn’t had much time to be altered by terrestrial influences.

“It’s really a great sample if you’re interested in studying something that has more or less been delivered straight from Mars, uncontaminated, to the Earth,” says planetary scientist Carl Agee of the University of New Mexico.

Other scientists agree but don’t rule out contamination entirely. “It sat around the desert for months,” says planetary scientist Harry McSween Jr. of the University of Tennessee, and the meteorite probably wasn’t collected under sterile conditions. “Nevertheless, it’s an interesting sample, in that it is probably less altered than others we have that weren’t collected immediately.”  

The meteorite provides evidence of weathering that occurred on Mars’ surface, says Hasnaa Chennaoui Aoudjehane, a geologist at Hassan II University in Casablanca, Morocco, and lead author of the report on the rock, published online October 11 in Science. “It’s really the first time that can be shown in a Martian meteorite excluding any terrestrial contamination,” she says. The team’s findings are in line with observations of Mars made by NASA spacecraft and rovers.

The new report suggests the meteorite formed from Martian lava rock that was worn down by weathering, possibly by liquid water. Then, about 700,000 years ago, something impacted the Red Planet and blasted a piece of that rock into space, on an ultimate collision course with Earth.

Tissint is a type of meteorite known as a shergottite, composed of volcanic rock rich in the elements iron and magnesium. The shiny black coating on the meteorite chunks betrays the roasting they underwent in the Earth’s atmosphere. The rocky interior is punctuated by black glassy bubbles and channels, formed when the impact on Mars created a shock wave that melted small pockets of rock. These glass bubbles contain a treasure trove of trapped Martian atmospheric gas and surface minerals.

“It’s sort of like having a little Martian environment tucked away inside that meteorite,” Agee says.

Many groups are studying Tissint, and much of the exciting research on this meteorite is yet to come, scientists say. But for Chennaoui Aoudjehane, a native of Morocco, the rock has a deeper meaning: “This meteorite is important for me and for my country,” she says.

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