As humans continue to explore the frontiers of space, the question of what kinds of life forms from Earth can survive the harsh conditions on other planets has become more pressing. If we transport micro-organisms from Earth to other worlds, will we seed life there, and potentially complicate the search for extraterrestrial life? Will these organisms potentially compromise the health of our astronauts, which is already weakened by space travel?
Last year, NASA scientists discovered 26 new resilient bacterial species inside their own ultra-sterile clean rooms at the Kennedy Space Center in Florida, built to prevent critters from hitching a ride on NASA spacecraft. These microbes survived UV sterilization, chemical scrubbing, and radiation. Researchers also discovered that some bacteria essential for human health can survive the extreme conditions of rocket launch.
Now Ph.D. candidate Tommaso Zaccaria has discovered 10 micro-organisms that could theoretically survive the unforgiving conditions on other planets, including several human pathogens, such as the bacterium Klebsiella pneumoniae, which can cause pneumonia.
At the German Aerospace Center in Cologne, Zaccaria simulated conditions on our moon, Mars, and the moons of Jupiter and Saturn, because water is found there. To recreate such environments, he exposed the microorganisms to harsh radiation, dehydration, and freezing. He found that extremophiles that live near volcanoes and glaciers were especially adaptable. Yeasts were the most resilient of all. And certain pathogens shrank after a simulated space trip to Mars, which made human immune systems less able to respond to them.
I spoke with Zaccaria about the fidelity of his simulations, the difficulties of sterilization in space, and the risk that we’re seeding other planets with life.
How closely can you simulate in a lab the conditions found on Mars or the moons of Jupiter and Saturn? What are the biggest gaps?
In our experiments, we tend to focus on the time of day when there’s a temperature of roughly 20 degrees Celsius on the surface of Mars. But this only happens at specific locations on Mars and during specific seasons. It’s also very difficult to simulate the whole radiation spectrum in the lab. We can only do specific wavelengths of UV radiation and certain specific ionizing radiation types. These are the biggest limitations. With the icy moons, we can’t simulate the very, very low temperatures. It can get to negative 200 degrees Celsius or thereabouts. But we can simulate all the other conditions.
You found that yeasts did better than bacteria in simulated space conditions. Does that tell us anything about what life on other worlds might look like?
My study was limited to 10 microorganisms. Among these 10, I found that the yeast were more resilient than the bacteria, but there could still be bacteria that are more resilient. As for what extraterrestrial microorganisms could look like, they could have some features that are similar to the yeast, yes—some specific survival methods and some specific metabolic functions that could be shared with yeast.
Do your findings tell us anything about why astronauts suffer accelerated aging and weakened immunity in space?
We already know that it happens in space. There are other studies that have focused on that. We just focused on the risks associated with possible bacterial infections that could take place in space. But we didn’t look yet at why immune aging works that way in space or why the human immune system suffers accelerated aging in space. This is something we want to look at in the future.
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But do you think the fact that these pathogens can become more infectious could have something to do with that?
We don’t know if they do become more infectious. What we found is that they evade the immune system, but this doesn’t mean that they cause more disease. It just means that the immune system doesn’t recognize them. It’s possible that the microorganisms also don’t cause disease, but this is something that we want to confirm with future experiments.
Do you know why the pathogens shrink and why shrunken pathogens evade the immune system?
We don’t have a 100-percent answer on that, but we think that what is taking place is that after the pathogens are exposed to Martian conditions, the cell structure changes due to the effects of desiccation—the absence of water—and the effects of radiation, UV, and X-ray, which might damage the antigens or the structures that are on the cells. And these structures are how the immune system recognizes these pathogens. If they’re damaged, the immune system won’t recognize them. It’s like a lock-and-key mechanism. If the key is broken, you cannot unlock the door.
What can your research tell us about how human immune systems function here on Earth?
My research could provide new insights into how people with altered immune functions on Earth could fight off these infections. Maybe they have autoimmune diseases or any other type of immune system dysfunction due to genetic factors or environmental factors. We see similarities between people who travel to space and people who have these forms of immune system dysregulation.
Why do you think those similarities exist?
Because the immune system probably doesn’t recognize foreign material in a similar way. In space, the immune system doesn’t work as well due to different factors like the effects of radiation, limited diet, and microgravity, and the immune system is fatigued. People on Earth who have specific autoimmune diseases, for example, have immune systems that fatigue in a similar way. It’s fatigued for a different reason, but the result is similar.
What does your research tell us about how we can better protect astronaut health? Are there practical measures you would suggest?
Focusing on pathogens in space is very relevant. This was something that hadn’t been looked at before. Most of the research in the past looked at extremophilic microorganisms, which can survive extreme conditions, but these microbes don’t cause disease in humans. They’re harmless. My findings suggest we need to focus some of the research currently being done on these specific pathogens I studied and many others. We only looked at four, but unfortunately, there are more pathogens around us. We should also focus on how to recognize them and how to try to get rid of them. We could develop new disinfection or sterilization techniques so that it’s harder for the pathogens to survive on the surfaces that we touch.
Does sterilization in space face any unusual hurdles?
It’s much more difficult to do than on Earth. For one thing, you have to bring the supplies up to space, which has a material and economic cost. Space agencies, including NASA, also have some limitations in regard to carrying into space chemicals that are flammable or combustible. We should try to find techniques to sterilize or disinfect surfaces which don’t make use of chemicals that pose combustion risk in space. Maybe one way to look at this would be to try to develop some surfaces which are antimicrobial from the start, to limit the growth of microorganisms.
You also found that lunar and Martian dust can damage the lungs. How quickly does that happen, and is it reversible?
It damages the lungs as soon as you breathe it in, so there’s not really a timeline associated with that, but of course, the effects accumulate over time, so the longer you breathe it in, the worse off you are. So it’s quite fast, but it also depends on which dust you breathe in.
How difficult is this damage to address? Is it permanent?
We didn’t look at whether the damage is permanent. The challenge with that is that if the particles of dust are a certain size, they can become stuck in the lungs, making them very difficult to get rid of. I’m not a human airways specialist, but I think that if the dust were a bit bigger, it would be easier to get rid of through coughing or other mechanisms. The challenge lies with the long-term results. We don’t know what those are yet, but we can say that the shorter, the better with the exposure to this dust. We wouldn’t recommend long-term exposure.
How likely do you think it is, given what you found, that we’re populating other planets with life through our travels into space?
For now, the chances are very low, because everything we’ve sent beyond the moon is only robotic, not human. The chances that we’ve spread life beyond the moon is very, very, very, very slim. But if and when human travelers are involved, it’ll be inevitable that microbial life will follow us. We have microorganisms on our skin, in our gut, which are there and help us digest, help our skin to function the way it does. So it’ll be extremely difficult to avoid. But for now, as it is today in 2026, the risk is extremely low. Even, for example, during the Apollo missions, when the astronauts arrived on the moon, the conditions of the moon are so challenging for life that we don’t expect anything to survive them, especially since the last mission was roughly 50 years ago. In that span of time, it’s difficult for anything to grow or survive.
So microorganisms can’t just hitch a ride onto a spacecraft without a human actually being part of that voyage?
No, the chance of a microorganism hitching a ride is there and is likely, but the chance that it survives ascent and the journey to Mars or the icy moons where it’s bombarded by radiation, by desiccation, is very unlikely. There might be some cellular components on the spacecraft surfaces, but by the time they reach their destination, they will be dead. 
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Lead image: siomay / Adobe Stock
