Mars meteorite hints at what’s hiding under the dust

The bulk of rocks on the surface of Mars probably look a lot like Black Beauty: "dark, messy, and beautiful," says Jack Mustard. (Credit: Lapis Ruber/Flickr)

A meteorite that’s more than 4 billion years old offers a clue to what’s beneath the red dust on Mars.

Discovered in the Moroccan desert, the meteorite (NWA 7034) is like no other rock ever found on Earth. But a new spectroscopic analysis suggests rocks just like it may cover vast swaths of Mars.

Martian meteorite NWA 7034
Designated Northwest Africa (NWA) 7034, and nicknamed “Black Beauty,” the Martian meteorite weighs approximately 11 ounces (320 grams). View larger. (Credit: NASA)

The meteorite’s measurements are a spot-on match with orbital measurements of the Martian dark plains, areas where the planet’s coating of red dust is thin and the rocks beneath are exposed, scientists say.

The findings suggest the meteorite, nicknamed Black Beauty, is representative of the “bulk background” of rocks on the Martian surface, says Kevin Cannon, a graduate student at Brown University and lead author of a new paper published in the journal Icarus.

When scientists started analyzing Black Beauty in 2011, they knew they had something special. Its chemical makeup confirmed that it was a castaway from Mars, but it was unlike any Martian meteorite ever found.

Annoyingly different

Before Black Beauty, all the Martian rocks found on Earth were classified as SNC meteorites (shergottites, nakhlites, or chassignites). They’re mainly igneous rocks made of cooled volcanic material.

But Black Beauty is a breccia, a mashup of different rock types welded together in a basaltic matrix. It contains sedimentary components that match the chemical makeup of rocks analyzed by the Mars rovers. Scientists concluded that it is a piece of Martian crust—the first such sample to make it to Earth.

Cannon and coauthor Jack Mustard thought Black Beauty might help to clear up a longstanding enigma: the spectral signal from SNC meteorites never quite match with remotely sensed specra from the Martian surface.

“Most samples from Mars are somewhat similar to spacecraft measurements,” Mustard says, “but annoyingly different.”

So after acquiring a chip of Black Beauty from Carl Agee at the University of New Mexico, Cannon and Mustard used a variety of spectroscopic techniques to analyze it. The work included use of a hyperspectral imaging system developed by Headwall photonics, a Massachusetts-based company. The device enabled detailed spectral imaging of the entire sample.

“Other techniques give us measurements of a dime-sized spot,” Cannon says. “What we wanted to do was get an average for the entire sample. That overall measurement was what ended up matching the orbital data.”

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The spectral match helps put a face on the dark plains, suggesting that the regions are dominated by brecciated rocks similar to Black Beauty. Because the dark plains are dust-poor regions, they’re thought to be representative of what hides beneath the red dust on much of the rest of the planet.

“This is showing that if you went to Mars and picked up a chunk of crust, you’d expect it to be heavily beat up, battered, broken apart, and put back together,” Cannon says.

That the surface of Mars would be rich in breccias like Black Beauty makes a lot of sense, given what we know about Mars, the researchers say.

“Mars is punctured by over 400,000 impact craters greater than 1 km (.6 miles) in diameter . . . ,” they write. “Because brecciation is a natural consequence of impacts, it is expected that material similar to NWA 7034 has accumulated on Mars over time.”

In other words, Mustard says, the bulk of rocks on the surface of Mars probably look a lot like Black Beauty: “dark, messy, and beautiful.”

Source: Brown University