A 1.3-billion-year-old tiny fragment from a Martian meteorite has a surprising “cell-like” structure which may have once held water or accommodated colonies of microbes, researchers say. The findings, published in Astrobiology last month, add to the increasing evidence that beneath the surface, Mars had all the conditions for life to form and evolve.

Back in 1911, about 40 rocks fell near the Abu Hommos district of Alexandria, Egypt. (One of them reportedly fell on a dog.) To examine the signature meteorite of the group—named Nakhla—a trio of researchers led by Elias Chatzitheodoridis from National Technical University of Athens took high-resolution images of the fragment, revealing the atomic layers of the material within.

They found an unusual feature embedded deep in the rock: a conspicuous clay ovoid. “In many ways it resembled a fossilized biological cell from Earth but it was intriguing because it was undoubtedly from Mars,” study co-author Ian Lyon at the University of Manchester says in a news release. “Our research found that it probably wasn’t a cell but that it did once hold water—water that had been heated, probably as a result of an asteroid impact.”

The hollow space, at about 80 microns long and 60 microns wide, was far larger than most terrestrial bacteria on Earth. "Despite the extremely biomorphic overall shape of the ovoid, it is highly unlikely that it itself was an organism," Chatzitheodoridis tells Space.com. "However, it could have been formed directly by microorganisms, or it could trap organic material that came from elsewhere.”

Large asteroids smashing into Mars in the past could have produced long-lasting hydrothermal fields that could sustain life on the Red Planet, even in later epochs. “It’s not too cold, it’s not too harsh. Life as we know it, in the form of bacteria, for example, could be there,” Lyon says. “It’s about piecing together the case for life on Mars—it may have existed and in some form could exist still.”

The team is now investigating possible biosignatures on Nakhla.

Images: JPL/NASA