Mars, as we know it, is a frigid and lifeless world—but a new study reveals a fresh hint to a much more happening past.
NASA’s Curiosity rover has found an array of medallion-sized, hexagonal mud cracks on the terrains of Mars’ Gale Crater. The distinctive shape of these patterns suggests the Red Planet was once much balmier and that it cycled through wet and dry episodes for millions of years, per the study published last week in Nature. These conditions are theorized to lead to the emergence of life.
“It’s quite a unique formation,” says study author William Rapin, a planetary scientist at the French Research Institute in Astrophysics and Planetology, to Vice’s Becky Ferreira. “It’s the first time we’ve seen that on Mars, actually, and it tells us a lot of details on how the climate was working at the time.”
New discovery alert: I've spotted evidence that Mars had wet-dry cycles that could have led to conditions for microscopic life to form!— Curiosity Rover (@MarsCuriosity) August 9, 2023
More on the hexagonal shapes in these preserved mud cracks and what they tell my team: https://t.co/u83os6Jpoe pic.twitter.com/7hnles5yp6
In 2021, the rover snapped photos of the unusual patterns caked onto the ruddy landscape as it scaled the three-mile-high Mount Sharp in Gale Crater. These cracks resemble the polygonal formations found in salt flats on Earth, such as those in Death Valley, reports Phie Jacobs for Science. Since these ridges on Earth formed during periodic wet-dry seasons, the scientists suspect that Mars once had a similar climate.
These patterns aren’t the first evidence of liquid water on early Mars. The Red Planet’s surface is awash with deltas, gullies and sedimentary deposits that indicate water once flowed to sculpt such geological features. The new study, however, is the first to paint an episodic reel of Mars’ hydrological seasons.
When fresh fissures form on drying mud, they’re usually T-shaped, at least initially. They stay that way unless water regularly rehydrates the soil, softening their corners into Y-shaped junctions. For example, a collection of mud cracks bears a T-shaped patten further downhill on Mount Sharp, on the Old Soaker rock slab where Curiosity previously wandered. This network of four- and five-sided polygons suggests the surface was historically wet and dried out one time, for good. But in the area with the six-sided shapes, it seems that drying happened repeatedly.
“It’s impossible to make this hexagonal pattern without regular periods of wet and dry,” Rapin tells Science.
For liquid water to pool and flow on Mars, the planet had to be much warmer than it is today. Previously, scientists hypothesized that one-off events such as a volcanic eruption or an asteroid impact could have caused global temperatures to spike. But the polygonal patterns reported in the new study strengthen a different argument—that the warm chapter in Mars’ climate history was one that persisted for thousands to millions of years, with alternating flooding and drying events.
“Early Martian geology was not the result of a sudden transient warming event,” Ramses Ramirez, a planetary scientist at the University of Central Florida who was not involved in the study, says to Science.
The recurring bouts of wet and dry conditions could have unlocked life on Mars, says Rapin in a statement from NASA. For life to emerge on a planet, it requires just the right amount of liquid water—not too much and not too little, either. As it turns out, a series of wet and dry spells might be just what life needs.
“Wet-dry cycles are helpful—maybe even required—for the molecular evolution that could lead to life,” he says in the statement.
On-and-off periods of water on Mars might have cooked up favorable conditions for chemical reactions that assemble compounds into biomolecules. In particular, these reactions can produce nucleic acids, a crucial component of DNA that’s part of all life.
But these climate cycles alone could not create life, as Sidney Becker, a researcher at the Max Planck Institute of Molecular Physiology in Germany who was not involved in the research, tells Sky & Telescope’s Colin Stuart. Mars would have also needed proper conditions in the atmosphere and the ideal mineral composition to be habitable.
If Martian life flourished in the past, the evidence could be etched into the rocks on that quiet planet. Unlike Earth, Mars doesn’t have tectonic activity, so its planetary history is preserved in the geologic formations on its surface. In this way, studying Mars could help fill in the blanks about life’s emergence on Earth, Rapin says to Science. “We could go to Mars to help solve that mystery.”