Mars is a dry, dusty planet, but evidence is mounting that water once flowed freely at its surface. Now, researchers have found patterns in Martian sediments that suggest the planet once had a cyclical climate similar to Earth’s. The study, which furthers our understanding of Mars’s history and its suitability for life, was published in Nature.
Unlike Earth, where plate tectonics constantly erases and reshapes landscapes, Mars has preserved fossilized rivers and lakes dating back billions of years. Since 2012, NASA’s Curiosity rover has been exploring these remnants, uncovering traces of simple organic molecules. The emergence of primitive life-forms hinges on specific environmental conditions that facilitate the spontaneous organization of water-soluble molecules into more complex organic compounds.
“Understanding the past environments on Mars is crucial for assessing its potential habitability and whether life ever existed there,” said planetary scientist William Rapin from the French National Center for Scientific Research, lead author of the study. “We have known that early Mars had wet areas but didn’t know much about how the water behaved over different periods or what it might mean to the planet’s ability to host and [control the] evolution of life on it.”
Rapin and his colleagues used data from the Curiosity rover to study Gale crater—a dry lake named after an amateur Australian astronomer who observed Mars in the late 19th century. Using data from Curiosity’s Mastcam and ChemCam, which photograph and measure rocks on the surface, the team spotted honeycomb-shaped sulfate deposits in sediments dating back 3.8–3.6 billion years, a period that roughly marked a transition in weathering process and environment on Mars.
Some of the deposits had cracks that likely formed as the sediments dried, whereas others had a hexagonal shape. The latter resemble patterns seen in landscapes on Earth that experience seasonal drying and wetting, Rapin explained.
“These salt deposits represent the first fossil evidence of a sustained, cyclical Martian climate that experienced both dry and wet seasons,” Rapin said. Previous lab experiments on Earth mimicking this cyclic climate have shown this kind of environment to be ideal for molecules to repeatedly interact, which is crucial for forming life’s building blocks, including RNA.
A Landscape for Life
Such wet-dry cycles could have been favorable for the emergence of life on Mars during the Noachian-Hesperian transition period, around 3.6–3.8 billion years ago. This period might have been more habitable than the earlier Noachian eon, which had perennially wet environments, Rapin explained.
That interpretation, which is based on existing theories about Mars, and the methodology used in the study are robust, said Robin Wordsworth, a planetary scientist at Harvard University. “The findings are consistent with the idea that Mars had episodic periods of wet and dry conditions rather than being perpetually warm and wet,” he said.
However, given the limited data on Gale crater’s past conditions, Wordsworth believes more studies must follow to further solidify this study’s conclusions. “The challenge in linking surface observations on Mars to climate scenarios and origin of life scenarios is you need multiple sources of information,” he said. Understanding the chemistry of ancient Martian fluids is crucial for assessing whether organic compounds could have formed and been preserved, he added.
—Vijay Shankar Balakrishnan (@VijaySciWri), Science Writer