(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 variety of scientific instruments that can analyze rock and dust samples and gather data about the Red Planet. But the instruments currently on Mars, as well as those designed for future missions, may not be sensitive enough to detect biosignatures, or signs of extant or ancient life.
To test the capabilities of these scientific tools, the 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 Martian analogue for scientists – even more so when scientists came across the desert’s Red Stone Jurassic fossil delta. The 100-million-year-old river bed resembles the 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 river more than 3 billion years ago, to look 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 NASA and the 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 to the Jezero crater and discovered that it was geologically similar, consisting 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 river bed and tested them with sensitive laboratory equipment. When pushed to the brink of their detection limits, the lab equipment analysis revealed a mix of biosignatures coming from both extinct and living microorganisms. Although incredibly dry, Red Stone is close to the ocean, where fog rolls in to provide water for microbial life.
Many of the microbe’s 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 resembles 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 river bed. Although highly sophisticated, the instruments were barely able to detect any molecular signatures—proving that the tools may not be sensitive enough to detect biosignatures accurately.
The study published Tuesday in the journal Nature Communications.
Detecting life will require advanced tools
Mars missions have searched 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 did exist on Mars billions of years ago, only low levels of organic matter are expected to remain, meaning it would be incredibly difficult to identify earlier signs of life on Mars with current technology, according to the study.
“The possibility of getting 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 researcher at the Center of Astrobiology in Madrid.
The study’s findings support the goals of the Mars Sample Return program, a multi-mission effort that will deliver rocks and soils from Mars to Earth, where scientists can analyze them using state-of-the-art laboratory equipment to look for unequivocal signs of life.
“Our results underscore the importance of returning samples to Earth to conclude whether life ever existed on Mars,” the researchers wrote in the study.
Care must be taken when evaluating the first Martian samples returned to Earth, Carol Stoker, a staff planetary scientist at NASA Ames Research Center in Mountain View, California, wrote in a commentary 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 whether unambiguous signatures of life can be found in the limited samples. We must be careful to interpret the absence of strong evidence of life as evidence of absence!”
One of the instruments tested will travel to Mars aboard the first European rover, called Rosalind Franklin, which is expected to launch to the Red Planet by 2028.
“(It) will carry a drill with the unprecedented ability to reach down to a depth of 2 meters (6.6 feet) to analyze sediments that are better protected from the harsh conditions of the Martian surface,” said study co-author Alberto G. Fairén, researcher. at the Center of Astrobiology in Madrid and visiting researcher at Cornell University’s Department of Astronomy, in a statement.
“If biosignatures are better preserved at depth, as we expect, there will be more abundance and diversity, and better preservation of biosignatures, in the deep samples. Our instruments in the rover will therefore have more chances to detect them.”