Mars rovers tasked with hunting for traces of biology can roll over microscopic life forms without smelling a thing, simply because their instruments are not up to the task.
A new study conducted in Earth’s oldest desert shows how current technology cannot always detect the signatures of life on our own planet’s surface. Let alone on Mars.
The researchers behind the study argue without improving our ability to identify long-dead ‘microbial dark matter‘, life on Mars will continue to elude us. Especially if the life we’re looking for existed billions of years ago when the planet was warmer and wetter than it is today.
Chile’s Atacama Desert has an ancient delta called the Red Rock, which contains sand and rock rich in hematite and mudstone. Geologically, this region is quite similar to parts of Mars, which is why astrobiologists often use it as a model for the Red Planet.
When researchers in Chile tested the redstone’s mineralogy with the best instruments available today, they uncovered some mysterious signs.
Almost 9 percent of the genetic sequences obtained using Next Generation Sequencing fell into the ‘unclassified’ category, while 40 percent of the remaining sequences could not be assigned to anything more specific than the highest of taxa, such as orders or domains.
Researchers from the Autonomous University of Chile (Universidad Autónoma de Chile) say their findings reveal “an unusually high degree of phylogenetic indeterminacy.”
The team has proposed a new concept to represent that uncertainty, what they call a “dark microbiome”. This term essentially refers to microorganisms that scientists can unknowingly detect via genetic sequencing exact what they are.
“Therefore,” researchers write, “the Red Stone dark microbiome may be composed of truly new extant species found nowhere else on Earth, but it may also be the case that such a dark microbiome actually represents the relict community of microbial species that used to inhabit the Red Stone Delta in the distant past, of which no extant relatives can be found in the existing sequence databases.”
The Red Stone samples were also analyzed by testbed instruments used on Mars or destined for Mars, showing that detection of microorganisms was far more challenging, with limited or no detection in most cases.
Last year, the Perseverance rover on Mars found “strong signs” of organic material as it rolled through an ancient river delta.
In the years before that, the Curiosity rover picked up signs of organic molecules in both sand and dried mud.
These are promising findings, but organic matter is not a sure sign of life. It is still unclear whether these molecules actually have a biological origin.
“Our analyzes of testbed instruments that are on or will be sent to Mars reveal that although the mineralogy of red rock matches that detected by ground-based instruments on the Red Planet, correspondingly low levels of organic matter will be difficult, if not impossible to detect in Martian rocks, depending on the instrument and technique used,” researchers in Chile conclude.
“Our results underscore the importance of returning samples to Earth to conclude whether life ever existed on Mars.”
For many years now, NASA has planned to retrieve their samples from Mars to take a closer look. But that is easier said than done. Traveling to Mars and back requires a space mission to go further than ever before.
The date for this historic moment is currently set at some time in the 2030s or 2040s. Hopefully our technology will be better equipped to take a good look at what we’ve found.
The study was published in Nature communication.