(CNN) The surface of Mars is a harsh frozen desert, but some microbes from Earth could temporarily survive there, according to a new study. And the researchers didn't even have to send microbes to Mars to find out.
The two planets may not seem very similar, but our stratosphere -- a layer of the atmosphere 20 miles above the Earth's surface -- has some qualities in common with Mars. Our home planet's stratosphere experiences low air pressure and high levels of radiation, and it's dry and cold -- much like the surface of the red planet.
Using the MARSBOx, or the Microbes in Atmosphere for Radiation, Survival and Biological Outcomes Experiment, scientists at NASA and the German Aerospace Center collaborated to send four types of microbes into the stratosphere on a balloon.
The study published Monday in the journal Frontiers in Microbiology.
"If a microbe can hack it up there, above much of the protective ozone layer, it just might be able to survive -- however briefly -- on a journey to the surface of Mars," said study coauthor David J. Smith, MARSBOx co-principal investigator and researcher at NASA's Ames Research Center, in a statement.
Microbes, or microorganisms, have an expansive reach on Earth. It's estimated that there are 1 trillion species of them on our planet. They can also be found living in harsh environments under varying extreme conditions.
Scientists at NASA need to know if these microbes could survive on Mars as they continue to send robotic explorers to the red planet on behalf of humans. That's why the mission teams behind these rovers, like the recently landed Perseverance rover, take the cleanliness of these machines very seriously before they're launched to Mars.
Perseverance is the cleanest yet. It's searching for signs of ancient life on Mars, and microbes from Earth could present a false positive during this search, or they could contaminate our planetary neighbor.
To test the likelihood of microbe survival on Mars, the research team placed millions of microbes, including dried and dormant fungal and bacteria spores representing four species of microorganisms, on quartz discs. These discs were placed inside aluminum boxes designed by the study collaborators at the German Aerospace Center.
A mixture of gases similar to those in the Martian atmosphere, which is dominated by carbon dioxide, was pumped into the boxes. A large science balloon carrying the experiment was released from Fort Sumner, New Mexico, on September 23, 2019.
Shutters were used to help shield the microbes from the sun during ascent and descent. But once they reached the Earth's stratosphere 24 miles up, the shutters opened and exposed them to the harsh radiation there. The microbes were exposed to this for more than five hours, along with temperatures averaging negative 20 degrees Fahrenheit.
In the stratosphere, there is a thousand times less pressure than we experience at sea level, as well as very dry air.
When the experiment returned to the ground, the scientists determined that two of the four species survived the journey, proving that these two could temporarily endure the harsh conditions of Earth's stratosphere and, potentially, the Martian surface.
"This research gives us a better understanding of which microbes could linger in environments once assumed to be lethal, like the surface of Mars, and gives us clues about how to avoid unintentionally bringing tiny hitchhikers with us to off-world destinations," said study coauthor Ralf Moeller, MARSBOx co-principal investigator and head of the Aerospace Microbiology Research Group at the German Aerospace Center, in a statement.
The surviving species included Staphylococcus capitis and Salinisphaera shabanensis. The first is a bacteria associated with human skin and the second is a bacteria that can be found in deep-sea brine pools.
Aspergillus niger, a fungus that is used in the production of antibiotics, was dried to send it on the experiment, and it was also able to be revived once it returned from Earth's stratosphere.
"Spores from the A. niger fungus are incredibly resistant -- to heat, harsh chemicals, and other stressors -- but no one had ever studied whether they could survive exposed in space or under intense radiation like we see on Mars," said co-lead study author Marta Cortesão, a doctoral student at Aerospace Microbiology Research Group at the German Aerospace Center, in a statement.
"The fact that after their MARSBOx flight we could revive them demonstrates they are hearty enough to endure wherever humans go, even off-planet."
It's possible that Aspergillus niger has a sunscreenlike pigmentation or a cellular structure that protects itself.
"This experiment raises a lot of questions about what genetic mechanisms are key to making microbes able to survive," Cortesão said. "Do they carry ancient evolutionary traits that provide them the ability to withstand harsh conditions, or does the adaptation to their current environment provide protection for many other environmental challenges?"
Future research could help scientists better determine why these microbes survived. A follow-up flight is being planned for MARSBOx in Antarctica, where both radiation from the sun and galactic cosmic rays from space are even more similar to Mars.
"These balloon-flown aerobiology experiments allow us to study the microbe's resiliency in ways that are impossible in the lab," Smith said. "MARSBOx provides an opportunity to predict survival outcomes on Mars and help establish the limits of life as we know it."
In the meantime, these findings could assist with planning future missions to Mars. "The renewed focus on Mars robotic and human exploration amplifies the need for additional Mars analog studies in the coming years," the authors wrote in the study.
"With crewed long-term missions to Mars, we need to know how human-associated microorganisms would survive on the Red Planet, as some may pose a health risk to astronauts," said co-lead study author Katharina Siems, a doctoral student in the German Aerospace Center's Aerospace Microbiology Research Group, in a statement.
"In addition, some microbes could be invaluable for space exploration. They could help us produce food and material supplies independently from Earth, which will be crucial when far away from home. Microorganisms are closely-connected to us; our body, our food, our environment, so it is impossible to rule them out of space travel."