Mars may have been habitable millions of years later than we thought

Analysis of minerals in a Martian meteorite suggest that the planet may have begun to be hospitable for life 30 million years later than previously thought

By Chen Ly

Deformations in a small mineral grain from a Martian meteorite hint that habitable conditions on Mars could have arisen later than we thought.

Billions of years ago, the inner solar system went through a phase of intense asteroid strikes known as the Late Heavy Bombardment. Previous analysis of meteorites suggest these impacts stopped on Mars 4.48 million years ago, allowing the planet to develop conditions that may have been advantageous for life by about 4.2 billion years ago.

Now there’s evidence to suggest that this period of bombardment may have actually ended millions of years later than thought.

Aaron Cavosie at Curtin University in Australia and his colleagues analysed 66 grains of zircon from a Martian meteorite called Northwest Africa 7034. It has been colloquially named “Black Beauty” due to its dark colour, and was once part of the Martian crust.

“To give you a sense of scale, you could set several of the grains side by side across the width of a human hair,” says Cavosie. “They are about 40 or 50 micrometres across.”

Out of the 66, the team found one zircon grain showed signs of impact damage. “We saw these little planes or lines, that we call twins, where the shock pressures were so high that atoms in zircon literally were rearranged and into a different direction in the grain,” says Cavosie.

The shock deformations found in the zircon grain are extremely similar to those reported in the three largest impact sites in the world, including the Chicxulub crater left behind from the asteroid wiped out the dinosaurs, he says.

The team dated the sample back to around 4.45 billion years ago, which suggests that large asteroid strikes continued 30 million years later than the proposed end of asteroid bombardment. This in turn suggests that the window of habitability on Mars may have started later than 4.2 billion years ago, because the planet’s surface needed to cool down enough to potentially support life.

“The process that made this zircon is unique to meteorite impact,” says Cavosie. While more evidence of shocked zircons dating back to this period would be welcome, there only needs to be one good example to display evidence of bombardment, he says.

Journal reference: Science Advances, DOI: 10.1126/sciadv.abl7497

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