On March 14, a journey that was originally supposed to be a little over a week — but was stretched out to nine months — began to come to an end. NASA astronauts Suni Williams and Butch Wilmore were selected for the first crewed test flight on Boeing’s Starliner and were only supposed to stay at the International Space Station for 10 days, but when NASA discovered several helium leaks and propulsion system issues on the spacecraft, the agency decided to send it back empty until another mission could be sent up to get the astronauts.
This isn’t like some low-gravity version of “The Terminal,” in which travelers are stuck in limbo due to some administrative glitch. Space can have devastating and profound health effects on astronauts, which means Williams and Wilmore’s extended stay on the ISS could result in pronounced impacts on their bodies.
Launching into space requires undergoing g-force more than double that of what we experience on Earth, which former NASA astronaut Dr. Sandy Magnus once described as feeling like having a “70-pound gorilla sitting on your chest.” But that’s the last of gravity astronauts feel before reentering the Earth’s atmosphere once their mission is complete, and once they enter orbit they will spend the rest of their time in space floating in their seats.
But the effects of gravity — or lack thereof — are just the beginning of how space manipulates the human body. Everything from worsening eyesight to genetic changes to skin rashes that develop upon arrival — even no longer feeling accustomed to the touch of fabric on one’s clothes — have been reported in people who have gone to space.
“When we get back, even to lift a pencil we will feel the weight.”
“In general, the environment in space causes an accelerated model for disease, and what we kind of say is an accelerated model for aging,” said Dr. Afshin Beheshti, director of the Center for Space Biomedicine at the University of Pittsburgh. “But you don’t age faster, it’s just that all of the things associated with aging, like cardiovascular risk or cognitive issues … Everything is kind of sped up in space because of that environment.”
This week, four astronauts took off to the ISS, where the spacecraft will pick up Williams and Wilmore before returning home. At this point, Williams and Wilmore have been in space for nine months, joining just eight other astronauts who have spent more than 200 days in space. (NASA astronaut Frank Rubio holds the record at 371 days.) From what we know about the impacts of space on health, it will take them some time to recover from the journey.
“When we get back, even to lift a pencil we will feel the weight,” Wilmore said in a CNN interview last month. “That’s the transition back.”
That’s in part because on Earth, the force of gravity constantly acts on the skeleton, which stimulates bone-building cells called osteoblasts that maintain our bone density. Without that force, bone density and muscles can atrophy and weaken, with bones becoming 1% less dense for every month spent in space without any measures performed to combat bone loss.
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Although Williams and Wilmore exercise daily to mitigate these effects, they will still likely have experienced significant bone density loss when they get back. Upon landing, Wilmore and Williams will be met with medical teams who can help them get started on a 45-day post-mission recovery program, said NASA’s Lead Flight Surgeon Dr. Stevan Gilmore.
“They work closely with trainers, dedicating two hours each day to return to their pre-flight baseline state of health and fitness,” Gilmore wrote to Salon in an email. “Generally, most crewmembers’ physiological systems recover within this timeframe.”
For comparison, after NASA astronaut Scott Kelly spent one year in space, he had to learn how to walk again, Beheshti said.
“Being a year in space like that, it definitely takes a while for them to recoup the damage done,” Beheshti told Salon in a phone interview.
Kelly participated in the Twin Study conducted by NASA, in which several biomarkers of his were compared to his twin brother (Sen. Mark Kelly) who stayed on Earth. After the space flight, Kelly had more symptoms of heart disease than his brother and showed symptoms of something called Spaceflight Associated Neuro-ocular Syndrome (SANS), in which blood and cerebrospinal fluid travels upward from the legs to the head without the force of gravity, impacting the brain and vision.
“He wasn’t wearing glasses before he went, but he came back and started wearing glasses,” Beheshti said.
Additionally, disruptions to the body’s internal clock can affect astronaut’s sleeping and eating cycles. Some studies have also shown that astronauts’ cognitive processing speeds were slower in space, although these changes returned to baseline upon return to Earth. Similar results were found in research testing cognition in civilians who went to space.
“Sometimes people actually perform better in space, and they’re more even more focused, in a way,” said Dr. Chris Mason, a professor of physiology and biophysics at Weill Cornell Medicine in New York. “But sometimes people get a little slower. It really depends on the crew member.”
Radiation is also much stronger in space without the protective ozone layer on Earth to buffer it, and it can have several impacts on the body at the cellular level. For each week that astronauts spend on the ISS, the radiation they experience is equivalent to about one year’s worth of exposure on Earth, although this can vary depending on how many solar flares or cosmic rays in space occur.
That radiation has been shown to impact the cell’s mitochondrial function, which can have downstream effects on the body, Beheshti said.
“The mitochondria is your bioenergetics, so your energy in your body is produced by all of the mitochondria in your cells,” Beheshti said. “When the bioenergetics are damaged, you can imagine that it has detrimental effects … impacting your immune system and circadian rhythm.”
Exposure to radiation at these levels has been associated with an elevated risk for heart disease, cancer, and other degenerative disorders that affect the eyes. Researchers have been able to measure several biomarkers in astronauts who went to space and found that exposure to radiation and antigravity significantly impacts immune function as well.
In one 2024 study published in Communications Biology, Mason found that astronauts who spent time in space had longer telomeres, or structures at the end of chromosomes which protect DNA. Although longer telomeres have been associated with youth, they are also linked to certain cancers.
Mason’s research also found that several genes involved with the immune system were activated with space flight, presumably as a mounted response to the stress the body is put under in these conditions.
“There are also anti-inflammatory markers called interleukins which get activated, and we’ve seen some of them in almost every mission, so we would expect that they would also have them here,” Mason told Salon in a phone interview. “We see a lot of genes for DNA repair get activated, like the body is detecting some of the damage and then repairing that damage, which is a normal adaptive response.”
These effects increase the longer astronauts are in space, although about 95% of these cellular changes return to baseline within a few weeks of astronauts returning to Earth, Mason said. For Kelly, 90% of gene changes that he experienced returned back to normal within six months. In Mason’s study, telomere changes returned to baseline within days, he said.
Still, there are individual differences that can influence how quickly an astronaut bounces back and scientists are constantly researching what influences disease risk for astronauts.
Scientists haven’t yet figured out a way to fully block radiation, which interacts with the body as fast-moving invisible particles that can break up DNA. However, efforts are underway to test new small molecules in rodents that could improve resistance to radiation. This could have implications not just for astronauts in space but patients on Earth having to undergo invasive radiation therapies for cancer.
Others are studying whether an induced form of “artificial hibernation” could protect against some of the harmful effects of radiation. In recent studies, stimulating the same process that squirrels and bears go through in the winter has been shown to reduce the toxicity of radiation.
“When there’s radiation damage caused to your body, you create reactive oxygen species and that causes downstream things to to impact your immune system and things like that while also suppressing your mitochondria,” Beheshti said. “But when your body shuts down in that hibernation state, like in these animals, those reactive oxygen species stop getting produced as much, and then there seems to be less damage caused by the radiation.”
Commercial space flight has taken off in recent years and billionaires like Elon Musk are increasingly pushing a move to Mars, and these issues highlight the innate challenges humans — who have evolved over millions of years to live under the influence of Earth’s gravity and atmosphere — face in trying to expand our reach in outer space.
Wilmore and Williams will undoubtedly require some time to recover from their long journey, but they dedicated years to preparing for the experience. Still, they don’t seem too bothered by the extra time they spent in orbit.
“I think both of us will be a little bit sad when that feeling of space leaves us after about 24 hours,” Williams said in the CNN interview last month. “That means that physically the spaceflight came to an end.”
CORRECTION: An earlier version of this story incorrectly stated that Starliner is a SpaceX spacecraft. Starliner was developed by Boeing.