As the Moon blocks the Sun’s light completely next week in a total solar eclipse, more than 50 high-altitude balloons in over 20 locations across the US will soar up to 100,000 feet in the sky. On board will be Raspberry Pi cameras, weather sensors, and modems to stream live eclipse footage. They’ll also have metal tags coated with very hardy bacteria, because NASA wants to know whether they will survive on Mars.

Every time we send a rover to the Red Planet, our own microorganisms latch on to them and hitch a ride across space. What happens to these bacteria once they’re on Mars? Do they mutate? Do they die? Or can they continue living undisturbed, colonizing worlds other than our own? To answer these questions we need to run experiments here on Earth, and the eclipse on August 21st provides the perfect opportunity.

“I said, oh my god, that’s like being on Mars!”

The balloons are being sent up by teams of high school and college students from across the US as part of the Eclipse Ballooning Project, led by Angela Des Jardins of Montana State University. When Jim Green, the director of planetary science at NASA, first heard that over 50 balloons were being flown to the stratosphere to live stream the eclipse, he couldn’t believe his ears. “I said, oh my god, that’s like being on Mars!” Green tells The Verge. NASA couldn’t pass on the opportunity.

The upper part of the Earth’s stratosphere — just above the ozone layer — is very much like the surface of Mars: it’s about minus 35 degrees Fahrenheit, with very rarified air, and it’s hammered by the Sun’s ultraviolet radiation. During the eclipse, conditions will get even more Mars-like: the temperatures will go down even further, and the Moon will buffer some of those ultraviolet rays to better resemble the radiation on the Red Planet. “It’s really quite an outstanding astrobiology and planetary protection experiment,” Green says.

The bacteria that will fly to the edge of space is a particular strain called Paenibacillus xerothermodurans. It was first isolated from soil outside a spacecraft-assembly facility at the Kennedy Space Center in Florida in 1973, says Parag Vaishampayan, an astrobiologist at NASA’s Jet Propulsion Laboratory. These bacteria form shields of spores that allow them to survive even when conditions turn deadly. It takes around 140 hours at 257 degrees Fahrenheit to kill 90 percent of these bacteria, Vaishampayan tells The Verge.

“These are some of the most resilient types of bacteria that we know of,” says David J. Smith, a researcher in the Space Biosciences Division at NASA's Ames Research Center.

Last week, Smith finished mailing the bacteria — which are not dangerous for people or the environment — to the student groups. (Only 34 of the balloons will carry the bacteria.) The microorganisms are dried onto the surface of two metal cards the size of a dog tag. One card will fly to the stratosphere, while one will remain on the ground to function as a control group. On eclipse day, the balloons will launch every 15 minutes or so from states that are in the path of the Moon’s shadow, Des Jardins says. They’ll fly for about two hours, reaching the stratosphere and eventually popping because of the pressure drop. Once they’re back on the ground (a parachute will slow down descent), the students will track them by GPS, recover the metal tags, and mail them back to NASA.

That’s when Vaishampayan and Smith will get to analyze how many bacteria have died, and whether their DNA has changed in any way. If some of them survive the flight, that might mean that these bacteria may have already survived a trip to the Red Planet as hitchhikers on a Mars rover. We don’t know for sure whether Paenibacillus xerothermodurans is actually on any Mars rover. (It was found outside the spacecraft-assembly facility, not on the spacecraft themselves, Vaishampayan says.) But even if it’s not, learning more about these resilient bacteria could help us understand how similar ones could behave on Mars, and help NASA better understand the risk of infecting other worlds.

After all, we send million-dollar spacecraft to other planets and moons to search for alien life, so it makes sense that we’d want to make sure these places are protected from Earth’s germs. Pushing organisms to the known limits of life can also help NASA find that life. If we know that resilient bacteria can’t withstand certain conditions, then we won’t look for life when those same conditions are found on other planets, Smith says.

“I don’t think it’s ever been done.”

NASA has conducted very few experiments with high-altitude balloons, and none with this particular strain of bacteria. So flying over 30 balloons at once, under such perfect Mars-like conditions that won’t be possible to replicate in the lab, is an amazing opportunity. “I don’t think it’s ever been done in terms of a coordinated astrobiology experiment happening across the entire continental United States on the same day,” Smith says. “This is spatial coverage that one could never dream of in other circumstances.”

Green hopes the experiment will also inspire the next generation of astrobiologists and planetary protection officers. He got into science when he was in high school and had the chance to use an observatory telescope to observe the Sun. Taking part in the Eclipse Ballooning Project might do the same for the students flying the balloons. “You never know what turns kids on [to science],” Green says. “You never know how excited they can be.”