The Curiosity rover has discovered hexagonal patterns in ancient mud on the Red Planet, which hints at cyclical wet and dry periods and boosts chances Mars once hosted life
By Alex Wilkins
9 August 2023
Mars may once have had seasons
NASA/USGS
Ancient Mars had seasonal weather similar to Earth’s, with alternating wet and dry seasons, according to mud patterns discovered by NASA’s Curiosity rover. These seasonal cycles may have helped form some of the more complex building blocks for life, such as RNA and basic proteins.
There is ample evidence that Mars once had liquid water in the form of lakes and rivers, but it was unclear whether these came from one-off events, such as meteor impacts or volcanic eruptions melting ice, or whether they were tied to a more global weather cycle.
Now, William Rapin at the University of Toulouse, France, and his colleagues have examined images from Curiosity and found a distinctive pattern of hexagonal ridges in mud from the Gale crater, a former lake, which they say can only be formed from repeated wet and dry environments, each lasting around a Martian year or less.
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“It’s the first time we can show that the climate sustained hydrological change seasonally, or wet and dry seasons,” says Rapin. “We knew the Earth had them, but we didn’t know of any other planets that did. Now we know Mars had seasons.”
The researchers think the ridges were originally cracks in mud that have dried out. The cracks, which tend to intersect at specific angles, would have been filled in by flooding and minerals. Some of this material would have been washed away, but a more resilient mix of mud and rock would have remained, forming the ridges. “Only a seasonal climate – something with high frequency, geologically speaking – can produce those cracks in the mud that got fossilised,” says Rapin.