Scientists have been studying a lagoon in southern Spain called La Esperanza to better understand the wet-to-dry transition that occurred on Mars. La Esperanza is an example of a temporary, or “ephemeral,” water body that fills up during periods of heavy rainfall and then dries out completely during periods of drought.
A new study proposes focusing on “time-resolved analogs” – dynamic and similar Earth environments where changes can be analyzed over many years – in the ongoing search for signs of life on Mars. Alberto Fairén, a Cornell University visiting scientist in astronomy, led an investigation in the extremely salty Tirez lagoon in central Spain, which had experienced alternating dry and wet periods for two decades before reaching total desiccation in 2015.
The key findings: If life existed on Mars when it had liquid water on its surface, its desiccation did not necessarily imply that life had vanished forever. Furthermore, lipids, such as fatty acids or their derivatives, are more resistant to degradation and should be prioritized in the search for life in a waterless world.
We conclude that any possible early ecosystems on Mars most likely collapsed when liquid water vanished, 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.
Alberto Fairén
When studying Mars, Fairén’s team concentrated on areas that had water ponds before drying up during the Noachian (around 4 billion years ago) and Hesperian (3.7 to 3 billion years ago) periods. Over the course of 25 years, they closely monitored Tirez’s gradual desiccation, using it as an opportunity to better understand the evolution of microbial communities in small, dried-out lagoons. Tirez samples were collected and analyzed in 2002, when the lagoon was in its early stages of desiccation, and again in 2021, when it was completely dry.
By studying La Esperanza, researchers hope to gain insights into how similar features on Mars may have formed and evolved over time. In particular, they are interested in studying how the sediment deposited by water in the lagoon changes over time, as well as how microbial life may have interacted with the changing conditions.
“We conclude that any possible early ecosystems on Mars most likely collapsed when liquid water vanished,” 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.”
Fairén stated that the group will continue to monitor Tirez, 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.
The study of La Esperanza is part of a broader effort to better understand the potential for past or present life on Mars, as well as to develop strategies for exploring the planet more effectively in the future.
