When the Tirez Lagoon in central Spain dried up for more than 20 years and completely dried out in 2015, the arid landscape began to resemble arid Martian plains. That similarity, it turns out, could be useful: Researchers are looking at the microbial inhabitants of the recently deceased lagoon to find out what might have happened to hypothetical life on Mars when the salty lakes dried up billions of years ago.
“The take-home message is that if life existed on Mars when the planet had liquid water on the surface, the global desiccation of Mars would not necessarily have meant that life was gone for good,” says Alberto G. Fairén , an astrobiologist at the Spanish Astrobiological Center in Madrid.
Analysis of microbes in Tirez soil samples from 2002 and 2021 for a study in Scientific Reports, Fairén and his colleagues found that single-celled organisms called prokaryotes had adapted to thrive in extremely dry sediments. These results suggest that microbes that evolved in wetter conditions could have persisted after the Red Planet dried out. The researchers also measured traces of fatty acids, called lipids, that form in cell membranes in the 2021 samples — and the team confirmed that these long-lasting molecules would be a good target when looking for signs of earlier life on other planets.
Astrobiologists often study extreme Earth environments that can resemble those of other planets. However, the Tirez team says their new study presents the first long-term “time analog” of environmental change on another world. Researchers were interested in the lagoon’s high salt concentration as a proxy for Jupiter’s moon Europa, which some have hypothesized might harbor life. But in 2020, Fairén got the idea to instead use the decades worth of lagoon data to learn about early lakes on Mars.
Because this type of research helps researchers understand distant worlds, it can also be useful closer to home. Time analogs raise “an interesting idea — that we need to explore more not only to understand Mars, but also our own planet,” said Nathalie Cabrol, chief scientist at the SETI Institute, which focuses on the search for extraterrestrial intelligence. Cabrol, who was not involved in the study, says there is a “great need” for research into how quickly Earth’s biospheres are changing due to climate change.
Fairén’s team is currently planning two new time analog studies. First, as Spain’s long dry spell ends, Fairén hopes to measure how Tirez’s microbes react to water re-entering the lagoon. Second, he wants to study ecological changes in polar environments where ice is melting faster and faster, to compare them to the period when Mars lost its surface ice. He is confident that such research will inspire other scientists to take advantage of changing environments for their own studies – to learn more about life on Earth and beyond.