Spanish lagoon used to better understand wet-to-dry transition of Mars

Alberto Fairén, visiting scientist of astronomy at Cornell University, led an investigation in the extremely salty Tirez lagoon in central Spain, which had experienced alternating dry and wet periods over the course of two decades before reaching total desiccation in 2015.

The key findings: If life existed on Mars when the planet had liquid water on its surface, its desiccation would not have necessarily implied that life disappeared for good. In addition, lipids -- such as fatty acids or their derivatives -- have a higher resistance to degradation and should be preferred targets in the search for life in a waterless world.

When analyzing Mars, Fairén's research group focused particularly on locations that contained water ponds before drying up during the Noachian (around 4 billion years ago) and Hesperian (3.7 to 3 billion years ago) periods. They closely monitored Tirez's gradual desiccation over 25 years, using it as an opportunity to better understand the evolution of microbial communities in small, dried-out lagoons.

Samples from Tirez were collected and analyzed in 2002, during the early stages of desiccation, and again in 2021, when the lagoon was completely dry.

"We conclude that any possible early ecosystems on Mars probably collapsed when liquid water disappeared," Fairén said, "but the changing environment would have triggered global ecological successions, with hypothetical microorganisms evolving strategies similar to those of microorganisms living in Tirez now, adapted to thrive at very low water activity in the desiccated sediments."

The group will continue to monitor Tirez, Fairén said, noting that any changes in its status regarding water content would be of interest.

"It would be particularly interesting if the ongoing dry decade in central Spain would experience some alleviation and we could witness at least a partial comeback of the water table," he said. "That would allow us to extend even more our concept of the astrobiological time-analog for Mars, because the desiccation of Mars was a stepwise process.