Earth’s driest place shows why it may be harder than we thought to find signs of life on Mars

By Ashley Strickland, CNN

Finding potential evidence of life on Mars may be more difficult than expected, according to new research.

Missions such as the Perseverance and Curiosity rovers are each equipped with a suite of scientific instruments that can analyze rock and dust samples and collect data about the red planet. But those instruments currently sitting on Mars, as well as those designed for future missions, may not be sensitive enough to detect biosignatures, or signs of existing or ancient life.

To test the capabilities of these scientific tools, researchers went to Chile’s Atacama Desert, the driest place on Earth and the world’s oldest desert. The arid desert has long been considered a Mars analog for scientists — even more so when researchers came across the desert’s Red Stone Jurassic fossil delta. The 100 million-year-old riverbed resembles Jezero Crater and its ancient river delta on Mars.

The Perseverance rover is currently exploring the crater and delta, the site of a lake and a river more than 3 billion years ago, to search for signs of ancient life and collect samples. The soil and rocks collected by Perseverance will eventually be returned to Earth in the 2030s by the NASA and European Space Agency’s Mars Sample Return campaign.

A team of researchers explored the Red Stone site in northern Chile to see how it compared with Jezero Crater and discovered it was geologically similar, comprised of sandstone and clay, as well as hematite — the same iron oxide that gives Mars its distinct red hue.

Mars-like conditions on Earth

The researchers collected samples from the riverbed and tested them using sensitive laboratory equipment. When pushed to the brink of their detection limits, the lab equipment analysis revealed a mixture of biosignatures that came from both extinct and living microorganisms. Although incredibly dry, Red Stone is near the ocean, where fog rolls in to provide water for microbial life.

Many of the microbe DNA sequences came from an unidentifiable “dark microbiome” — a nickname given to the genetic material of previously unknown microorganisms. The researchers coined the term because it’s similar to dark matter — a hypothetical form of matter in the universe that remains unidentified.

The researchers took things a step further by testing four scientific instruments designed to explore the red planet on samples they collected from the ancient riverbed. Although highly sophisticated, the instruments were barely able to detect any molecular signatures — proving that the tools may not be sensitive enough to accurately detect biosignatures.

The study published Tuesday in the journal Nature Communications.

Detecting life will require advanced tools

Mars missions have been searching for signs of life on the red planet since the first Viking landers arrived on Mars in the 1970s. The more advanced instruments on NASA’s subsequent rover missions have detected simple organic molecules, but the molecules may have been created through chemical reactions unrelated to life.

If life existed on Mars billions of years ago, only low levels of organic matter are expected to remain, which means that identifying past signs of life on Mars will be incredibly difficult with current technology, according to the study.

“The chance of obtaining false negatives in the search for life on Mars highlights the need for more powerful tools,” said lead study author Dr. Armando Azua-Bustos, a research scientist at the Center of Astrobiology in Madrid.

The study’s findings support the goals of the Mars Sample Return program, a multimission effort that will deliver Martian rocks and soils to Earth, where scientists can analyze them using state-of-the-art lab equipment to look for unequivocal signs of life.

“Our results stress the importance in returning samples to Earth for conclusively addressing whether life ever existed on Mars,” the researchers wrote in the study.

Care will need to be taken when evaluating the first Martian samples returned to Earth, wrote Carol Stoker, a staff planetary scientist at NASA Ames Research Center in Mountain View, California, in a Comment article accompanying the study. Stoker was not involved in the research.

“Any biological activity in these samples presumably took place billions of years ago, and only a few small samples can be brought to Earth for study,” Stoker wrote. “It remains to be seen if unambiguous signatures of life can be found in those limited samples. We must be cautious about interpreting absence of strong evidence of life as evidence of its absence!”

One of the instruments tested will travel to Mars aboard the first European rover, named Rosalind Franklin, which is expected to launch to the red planet by 2028.

“(It) will carry a drill with the unprecedented capability of reaching down to a depth of 2 meters (6.6 feet) to analyze sediments better protected against the harsh conditions on the Martian surface,” said study coauthor Alberto G. Fairén, research scientist at the Center of Astrobiology in Madrid and visiting scientist in Cornell University’s department of astronomy, in a statement.

“If biosignatures are better preserved at depth, which we expect, there will be more abundance and diversity, and better preservation of biosignatures, in those deep samples. Our instruments in the rover will therefore have more chances to detect them.”

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