Meteorite left Earth then landed back down after round trip to space

Most of the meteorites found on Earth come from asteroids, but a few come from other bodies like Mars and the moon. Now, researchers say they have discovered a new kind - a rock originally from Earth that went to space then came back

The meteorite NWA 13188 seems to have travelled to space and back
Albert Jambon

A meteorite found in the Sahara desert in Morocco may have originated on Earth, before being blasted into space and returning from orbit thousands of years later. If confirmed, this boomerang space rock would be the first of its kind we know about.

Almost all the meteorites we have found come from asteroids, but a tiny fraction are from planetary bodies, such as Mars and the moon. These come from violent impacts that launch debris into space before later falling to Earth. Astronomers have shown that debris from similar impacts on Earth may also have fallen back to its home planet, but we have yet to find a compelling sample.

Now, Jérôme Gattacceca at the French National Centre for Scientific Research and his colleagues think they may have found a 600-gram meteorite from Earth. The rock, called NWA 13188, has the same chemical make-up as volcanic rock from our planet. It also has a thin layer of melted crust consistent with an impact and contains isotopes of elements that only form when an object has been bombarded with cosmic rays in space.

“It’s a meteorite from the Earth that has spent time in space, between 2000 and a few tens of thousands of years,” Gattacceca told the Goldschmidt geochemistry conference in Lyon, France, on 11 July.

NWA 13188 was originally found in the Sahara desert by a Bedouin group, which scours the landscape for potential meteorites to sell, so its exact location is unknown. It was certified as a meteorite by the Meteoritical Society in 2021, but was classified as “ungrouped” because its origin couldn’t be determined.

When Gattacceca and his team examined the rock, they found it had a similar chemical make-up to rocks on Earth, such as the same oxygen isotope fingerprint, as well as geological structures made at the boundary between tectonic plates, which only Earth has because other planets have no plate tectonics.

They then looked for evidence of irradiation from cosmic rays, which produce elements like beryllium-3 and helium-10 in asteroids. The levels of these elements were lower than in other meteorites, but were still significantly higher than any material found on Earth. This suggests that NWA 13188 spent a brief period outside Earth’s magnetic field, from a few thousand to possibly up to 100,000 years, says Gattacceca.

But not everyone agrees. “When you’re claiming extraordinary hypotheses, you need extraordinary evidence to back it up. I am still unconvinced,” says Philippe Claeys at the Free University of Brussels (VUB) in Belgium.

The lack of a known impact crater, which Gattacceca estimates should be around 20 kilometres wide, counts against it, says Claeys. “When you have an impact crater that young, you would have an impact melt that is still ‘hot and smoking’ — it would be really hard to miss.”

Gattacceca and his team are now trying to determine the age of the meteorite more accurately, using argon and carbon dating, which will help them narrow down a potential source.

There is also a question of whether the object can even be called a meteorite if it comes from Earth and only orbits for a relatively short time. There are many other rocks that reach high in Earth’s atmosphere from processes like volcanic eruptions, says Stepan Chernonozhkin at the University of Leoben in Austria. “If you define an Earth meteorite, you’re stretching the definition of meteorite.”