You don’t need boots on the ground on Mars to learn about its geology. All you need is a rock from the Red Planet’s surface. And researchers can find them right here on Earth. Of tens of thousands meteorites discovered on Earth, less than 200 came from Mars.

Wait, rocks from Mars are found on Earth? Yep. Thanks to a thin atmosphere and weak gravity (about 38% of Earth’s), impacts can fling rocks off Mars’ surface and into space. Then, the rock needs to make its way to Earth. Which isn’t something that happens fast.

A rock tossed off the surface of Mars with enough velocity to escape can take millions of years to reach Earth.

In 2012, a meteorite was discovered in Algeria. Designated ‘Northwest Africa 7635,’ this meteorite is believed to have left Mars 1.1 million years ago. By studying the effects of cosmic radiation on the meteorites, researchers can come up with how long ago the meteorite left Mars’ surface. This particular meteorite was exposed to cosmic rays for the same time as 11 other meteorites.

“What we interpret from that is that all 11 were knocked off Mars at the same time,” says Marc Caffee, a member of the research team. “But this one was different than the others.”

‘Northwest Africa 7635’ is much older. The other ten meteorites were 500 million years old and were formed from cooling magma. ‘Northwest Africa 7635’ was much older at 2.4 billion years old.

Mars meteorite

‘Northwest Africa 7635’ weights just under 7 ounces and can easily fit in your hand. Credit: Mohammed Hmani.

“What this means is that for 2 billion years there’s been sort of a steady plume of magma in one location on the surface of Mars,” Caffee says. “We don’t have anything like that on Earth, where something is that stable for 2 billion years at a specific location.”

That’s because plate tectonics on Earth are constantly shaping the surface. On Mars, that doesn’t happen.

Take Olympus Mons for example. It holds the record for the largest volcano discovered in the solar system. The lack of plate tectonics allows volcanoes to grow to such sizes. It also makes it possible for a volcano like the one Northwest Africa 7635 to continuously erupt for billions of years.

The constant resurfacing, whether from volcanic activity or weather, makes finding Martian meteorites (and any meteorites) on Earth difficult. Barren landscapes like Antarctica and deserts across the world are the best places to find them. Each year, about 1,000 meteorites are found. Only a handful get scientists talking like this one.

“These meteorites are allowing us to conduct geologic science on the surface of Mars, and we haven’t even been there yet,” Caffee says.

As for where this meteorite came from on Mars? That’s still an open question. Meteorites from Mars can tell us broad things about Mars’ geology. But it’s going to take men and women on the ground to learn about specific areas of Mars.