Over the past few years, the Curiosity rover has dug up clues suggesting that Mars’s Gale Crater once hosted a liquid-water lake.
Now, a new report says that the lake may have been long-lasting and chemically diverse—two qualities that suggest, if the lake were on Earth, that it would have supported a rich diversity of microbial life.
In a paper published in Science last week, Joel Hurowitz of Stony Brook University describes an ancient lake that was chemically divided, with oxygen-poor water in deeper parts of the lake and oxygen-rich water closer to the surface. Different microbes thrive at different oxygen concentrations, meaning each layer of the lake would have been capable of supporting a different form of microbial life.
The analysis of the crater’s layers of sediment and chemical contents also suggest the planet would have been warm enough during the period spanning 3.1 to 3.8 billion years ago to support an aquatic lake more or less continuously. The rover has now traveled more than 100 meters vertically up the lake bed, allowing the team to say with more certainty that the lake was sustained for a long period of time.
Since the scientists are studying rocks that are billions of years old on a planet a hundred million miles away, it can be difficult to detect the subtle signatures left by the lake. “I think [Hurowitz’s] seminal contribution is the chemistry,” said Raymond Arvidson, a scientist on the Curiosity mission who did not contribute to the new paper.
The precise data from the rover allowed the mission team to understand “the detailed and very nuanced changes in chemistry within the lake and changes in the environment over time,” said Ashwin Vasavada, a project scientist at NASA’s Jet Propulsion lab and a co-author of the paper. “I’m impressed with the level of detail that our [scientific equipment] was able to extract from these rocks,” he said.
The rover landed in Gale Crater in 2012 with the aim of determining whether the planet had ever been habitable to life found on Earth. Curiosity landed at the foot of a five-kilometer tall mountain containing tens of millions of years of climate data locked in its layers of sediment—an ideal window into Mars’ climatic history. In 2014 and 2015, John Grotzinger of Caltech used data from Curiosity to argue that Gale Crater contained a liquid-water lake at some point between 3.1 and 3.8 billion years ago. He also characterized the physical makeup of the crater, determining, among other things, the ages of the layers. Hurowitz developed his theory by matching the chemical data to Grotzinger’s physical model.
These new findings suggest that Mars once supported a range of chemical environments that may have shared more in common with present-day Earth than scientists previously believed. “The more we look at Mars the more complicated it becomes and the more interesting it becomes,” Arvidson said. “And the more it looks like portions of the lake were habitable 3.18 to 3.8 billion years ago.”