Mars may now be a dry and barren desert, but new evidence has emerged that this was not always the case and that the climate is changing, perhaps seasonally, in ways that could support the emergence of life. The pattern of hexagons in Gale Crater points to a history of repeated cycles of wet and dry conditions, allowing minerals to dry out between wet periods, creating distinct formations that have since been fossilized in the rock.

“We observe centimeter-scale polygonal ridges excavated by sulfate enrichments attached to Y-shaped joints that capture cracks formed in fresh mud by repeated wet-dry cycles of regular density,” wrote a team led by geochemist William Repin of Sabatier Fields University. in France.

“Instead of sporadic hydrological activity caused by impacts or volcanoes, our findings point to a persistent, cyclical, possibly seasonal, climate on early Mars.”

The consequences of this go beyond a more Earth-like climate. They add weight to the evidence that conditions on early Mars supported the emergence of biochemistry, the molecular basis of life.

Because the surface of Mars has not been replenished by tectonic activities, it preserves an extensive geological record of Martian history dating back to 4.3 billion years ago. In this record, we find plenty of evidence of a wet past, with lakes, rivers and oceans glistening on the Martian surface years ago.

Putting together the hydroclimate of early Mars is a little more difficult. But Repin and his team have shown that it is possible if you know how to take care of it. At the floor of Gale Crater, where the Curiosity rover explored, they found a series of well-preserved hexagonal patterns in sedimentary rocks rich in calcium and magnesium salts, spanning two time periods from about 3.6-3.8 billion years ago. It is known as Noisian and Hesperian.

Based on what we’ve seen here on Earth, we know the types of processes that can create these patterns in a dry basin. And after examining the options, the researchers concluded that the most likely explanation was drying out of the wet mud.

And not just one-time drying. Wet, drying mud cracks in T-sections. Aging during repeated drying cycles creates Y-shaped crack intersections, resulting in a hexagonal pattern.

The concentration of salts in the patterned rock is also much higher than in the bedrock, indicating that salts are depositing there – possibly as brine seeps from the silt and then evaporates, leaving the salt behind.

Finally, the thickness of the patterned rock indicates that regular wet-dry conditions existed on Mars for a long period of time, from thousands of years to possibly millions of years.

We don’t yet have evidence of microbial life on Mars, but these cyclical conditions would be suitable for organizing organic molecules into complex compounds. We know that there are organic molecules on Mars, and they’re probably common. Weather cycles are another piece of the sustainability puzzle.

“Addition of direct evidence from the repeated series of wet-dry cycles presented here supports the conclusion that conditions in ancient Gale Crater favored prebiotic polymerization processes,” the researchers wrote.

“Our findings suggest that the transitional period from Noachian to Hesperian may have been favorable for the emergence of life—perhaps more favorable than the early Noachian eon, with the potential for a persistent wet surface environment.” Source