There’s no evidence (yet) that microbes currently live on Mars.
But if microscopic Martians do exist, they might have an absolutely metal way of traversing the red planet’s inhospitable plains.
Using Chile’s Atacama Desert as a proxy for Mars, a team of researchers has collected data that suggests bacteria, fungi, and other single-celled organisms may hitch rides on wind-borne dust to colonize extreme environments, sometimes from dozens or hundreds of miles away. The study, published today in the journal Scientific Reports, underscores the remarkable ability of single-celled creatures to thrive in some of the world’s harshest habitats. And if the results hold true for Mars, they may give the search for extraterrestrial life something of a second wind.
Regardless of the status of life on modern Mars, the findings also raise concerns about something far less theoretical: The possibility that hardy foreign microbes, ferried in by spacecraft or astronauts from Earth, could use this dust-surfing strategy to disseminate over the red planet’s surface.
“This is a tantalizing first look at the types of organisms that could be transported on dust by wind…in one of the best known and best studied Mars analogs on Earth,” says NASA Planetary Protection Officer Lisa Pratt, who was not involved in the study. “[That] brings up concerns about contamination, and how we might inadvertently bring terrestrial microbes to another destination.”
At first pass, dust might not seem like a great way to get around. But wind is, well, a force of nature—one powerful enough to chauffeur specks of dust across thousand-mile stretches of land and sea. If a tiny cell were to glom onto globetrotting grime, it could quickly find itself on quite the sightseeing expedition.
And here on Earth, it seems microbes have literally caught on to this idea: Some journey to the Swiss Alps or the Caribbean atop Saharan sands; others latch onto particles making the trek from China to Japan.
But this tumultuous mode of transportation remains poorly understood under even the best of circumstances. And flying around on filth definitely comes with risks—especially when your final destination is Chile’s Atacama Desert, one of the harshest habitats on Earth. Blanketing a 600-mile-long strip of land along the Pacific Ocean, this vast, barren landscape is punishingly dry, with certain regions receiving just 0.05 inches of rain each year. Thousands of feet above sea level, ultraviolet radiation hammers down on the Atacama sands, which run low in nutrients, but high in moisture-sapping salts. The Atacama is an environment so extreme that it’s widely considered our planet’s closest approximation to the conditions of its rugged red neighbor.
That’s a lot for a single airborne cell to deal with. In addition to a rough-and-tumble ride, dust-surfing microbes would need to contend with dehydration and exposure to radiation—all before touching down in potentially toxic soil. But the Atacama has surprised researchers before: Despite the desert’s parched climate, in recent years, several species of bacteria, fungi, and other microbes have been unearthed in its salty sands.
For study author Armando Azua-Bustos, a microbiologist at the Center for Astrobiology in Spain, this raised the possibility that, even in these bleak desert locales, life itself…blows.
To test this possibility, Azua-Bustos and his colleagues journeyed to the Atacama to catch wayfaring microbes in the act. During the spring and summer of 2018, the researchers planted Petri dishes—some spiked with nutritious agar, some without—in a few of the desert’s driest spots. After an hour, they collected the plates, along with whatever dusty cargo they’d picked up.
Even as the team hauled their cache back to the lab, Azua-Bustos remained skeptical that there would be survivors. But within a few days, he was surprised to find colonies of bacteria and fungi sprouting atop the agar-coated plates. Some were sparse and fuzzy; others were thick and smooth. And all were alive.
DNA extracted from these colonies, as well as off particles of dust itself, revealed a final tally of more than 30 bacterial and fungal species. It’s not possible to pinpoint where exactly the microbes hailed from, Azua-Bustos says, but several of them are typically found near oceans, or cohabitating with plants in habitats dozens, if not hundreds, of miles away.
Of course, the Atacama isn’t usually lined with agar plates, so it’s unclear how many of these microbes would actually be able to hack it in desert sands alone. “Dispersal is only the first part of the story,” says study author María-Paz Zorzano, also an astrobiologist at Spain’s Center for Astrobiology. What comes next, she adds, is figuring out which bacteria and fungi are best suited to persist after their final descent—and why.
In the meantime, the study’s proof-of-principle finding “is a really great contribution,” says Kimberley Warren-Rhodes, an astrobiologist at SETI who was not involved in the study. “It’s a big step to figure out that microbes are being moved around in dust storms in even extreme environments, and that they might survive local transport.”
That could have implications for Mars, which is infamous for its dust storms. The fierce winds that drive them can sometimes kick up enough schmutz to shroud the entire planet, generating plumes so big they’re visible to telescopes on Earth. If life exists on the red planet (and that’s still a big if), it may be more widespread than once thought.
“We don’t necessarily have to think about the possibility of life existing only in places that have sustained, habitable conditions,” says Jennifer Buz, a planetary scientist at Northern Arizona University who was not involved in the study. “We can think of the whole planet as fair game for a microbe to land and exist.”
No matter how hard you squint, though, the Atacama is not Mars. The Martian atmosphere is notoriously thin and dominated by carbon dioxide. And far more UV radiation reaches the red planet’s surface, which also experiences massive fluctuations in temperature due to the lack of insulation.
The dynamics of travel in the Atacama are also unlikely to translate off planet. The low density of Martian air alters how wind carries the planet’s dust, which differs in size and composition from the stuff found on Earth. These discrepancies could change how particles move, as well as how long it takes for them to settle.
“It’s always a leap to go from Earth to Mars in terms of biology and ecology,” Warren-Rhodes says.
Still, the mere possibility of microbial mobility is important to consider in light of human space travel, Pratt says. On Earth, microbes are ubiquitous, and we can’t send completely sterile spacecrafts into the cosmos. If any microbial stowaways survived the trip into interplanetary space, dust storm winds could easily spread them far and wide, potentially imperiling the red planet on a global scale, she says. And the inverse scenario could apply as well: Should Martian life exist, it could potentially infiltrate Earth by way of windblown probes.
We can’t prepare for that future, though, without understanding the forms of life we’re dealing with, Pratt says. Studies like these, she adds, “take us a step closer to being prepared for Mars.”