Space is not the lifeless void most people imagine. Right now, seven astronauts orbit Earth on the International Space Station alongside dozens of species of fungi, bacteria, plants grown for food, and even microscopic animals tough enough to survive the vacuum outside. Beyond our own spacecraft, several places in the solar system have the raw ingredients that could support life, and telescopes are scanning distant planets for chemical hints of biology. Here’s what we actually know about living things in, on, and around space.
Humans Living in Orbit
The most obvious residents of space are people. A crew of seven typically lives and works aboard the International Space Station, circling Earth every 90 minutes at roughly five miles per second. During crew handovers, the population temporarily climbs higher. Astronauts stay for missions lasting about six months, though some have exceeded a year.
Living in microgravity takes a serious toll on the human body. The hip bone alone loses 1% to 1.5% of its mass per month, adding up to 6% to 10% over a standard six-month stay. Astronauts combat this with about two hours of daily exercise, but bone and muscle loss remain among the biggest obstacles to longer missions, like a trip to Mars.
Tardigrades: The Toughest Animal in Space
Tardigrades, also called water bears, are pinhead-sized animals found in moss, soil, and ocean sediment all over Earth. In 2007, a European Space Agency mission strapped two tardigrade species to the outside of an uncrewed Russian spacecraft and opened the door to space. After 10 days of direct exposure to the vacuum, almost all of them had dried out into a dormant state. Once brought back inside and rehydrated, they bounced right back to normal activity and even reproduced.
The vacuum alone wasn’t the problem. Tardigrades shielded from radiation but exposed to the vacuum survived easily. Those hit with UV-A radiation mostly pulled through as well. But UV-B radiation was devastating: survival rates dropped to 10% to 15% after a few days, and tardigrades exposed to both UV-A and UV-B died entirely. Lab tests suggest tardigrades can survive indefinitely in a vacuum as long as they’re protected from the harshest solar radiation.
Fungi Thriving Inside the Space Station
The ISS is not sterile. Surveys of its interior have found a surprising variety of fungal species growing on surfaces and floating in the air, with Aspergillus, Penicillium, and Saccharomyces (brewer’s yeast) being the most common. The radiation levels inside the station, roughly 4 centigray per year, are not strong enough to kill fungi. As long as humidity levels are sufficient, they grow just fine.
Many of the fungi found aboard the station are pigmented or melanized, which appears to be more than coincidence. Melanin, the same dark pigment found in human skin, acts as a radiation shield for these organisms. It works in two ways: physically blocking radiation and neutralizing the toxic molecules that radiation generates inside cells. Researchers studying fungi from heavily irradiated environments like Chernobyl found that some melanized species don’t just tolerate radiation; they actually grow toward it, possibly harnessing the energy. This has sparked interest in using fungal melanin as a lightweight radiation shield for future deep-space missions.
Plants Grown and Eaten in Orbit
NASA’s Veggie growing system has successfully produced several crops aboard the ISS, including three types of lettuce, Chinese cabbage, mizuna mustard, red Russian kale, zinnia flowers, and chile peppers. Crew members have harvested and eaten some of these plants in orbit. In 2018, astronaut Serena Auñón-Chancellor harvested red Russian kale and dragoon lettuce just in time for Thanksgiving, reporting the lettuce was “delicious” with a little balsamic vinegar.
Growing food in space is about more than nutrition. Plants help recycle carbon dioxide, contribute to humidity control, and provide a psychological boost for crews confined to a small metal tube for months. NASA views space agriculture as essential technology for eventual Mars missions, where resupply from Earth won’t be practical.
Could Anything Live on Mars?
Mars is the most studied candidate for life beyond Earth, and the evidence so far is tantalizing but inconclusive. NASA’s Curiosity rover has detected methane in the thin Martian atmosphere, and the levels cycle seasonally, peaking during northern summer. Background concentrations in Gale Crater range from about 0.24 to 0.65 parts per billion, with occasional surges reaching nearly 6 parts per billion.
On Earth, methane is overwhelmingly produced by living organisms. On Mars, the source remains unknown. It could come from microbes living underground, or it could come from purely geological reactions between hot water and certain types of rock. No instrument on Mars can yet tell the difference. What the methane fluctuations do confirm is that Mars is not geologically dead, and something beneath the surface is actively releasing gas into the atmosphere.
Europa’s Hidden Ocean
Jupiter’s moon Europa is covered in a thick shell of ice, but beneath it lies a saltwater ocean that may contain more liquid water than all of Earth’s oceans combined. This ocean has the four ingredients scientists consider necessary for life: liquid water, essential chemical elements, a source of energy, and long-term stability.
The energy piece is especially interesting. Jupiter blasts Europa’s surface with intense radiation, which transforms water ice and embedded minerals into oxygen-rich compounds called oxidants. Meanwhile, at the ocean floor, seawater cycling through hot rock creates a chemically opposite environment. If these two chemistries mix, perhaps through cracks in the ice or geological churning, the resulting energy gradient is exactly the kind of process every known life form on Earth uses to power its cells. NASA’s Europa Clipper mission, currently en route, will assess whether these conditions actually exist at the scale needed to support biology.
Searching for Life on Distant Planets
Beyond our solar system, the James Webb Space Telescope is analyzing the atmospheres of exoplanets for chemicals that might signal life. One planet that has drawn particular attention is K2-18 b, a world about 120 light-years away that orbits in its star’s habitable zone and has a water-rich atmosphere.
In April 2025, a team led by researchers at the University of Cambridge reported detecting dimethyl sulfide (DMS) in K2-18 b’s atmosphere at a statistical confidence of 3 sigma. On Earth, DMS is produced almost exclusively by marine organisms, so this seemed like a potential smoking gun. But a follow-up NASA-led analysis found the signal at a weaker 2.7 sigma, well below the 5-sigma threshold scientists require for a definitive detection. That 5-sigma bar means there’s only a 0.00006% chance the signal appeared by random noise.
More importantly, modeling showed that non-biological processes, particularly chemical reactions triggered by starlight in hydrogen-rich atmospheres, can also produce DMS. So even a confirmed detection might not prove life exists there. The answer may depend on the planet’s structure: if K2-18 b has a thin atmosphere over a liquid water ocean, biology remains the only known explanation for DMS. If the atmosphere is deep and thick, chemistry alone could account for it. For now, the hints persist, but proof remains out of reach.
What We Know for Certain
The confirmed residents of space are all from Earth: humans, fungi, bacteria, plants, and the occasional experimental animal. Tardigrades have proven that animal life can endure the vacuum and radiation of open space, at least briefly. Melanized fungi appear almost comfortable in the radiation-heavy environment of low Earth orbit. And every crop harvested on the ISS brings us one step closer to sustaining human life far from home.
Whether anything lives independently in space, without being sent there by us, remains one of the biggest open questions in science. Mars has unexplained methane. Europa has an ocean with the right chemistry. Distant exoplanets show faint, ambiguous signals. None of it is proof, but the list of plausible places keeps growing.