Four astronauts spent 3 days in space. Here's what it did to their bodies and minds.

Space changes you, even on short trips off-planet.

Four people who spent three days off Earth in September 2021 experienced physical and mental changes that included modest declines in cognitive tests, immune system stress and genetic changes within their cells, scientists report in a package of published papers Tuesday in the journal Nature and several other related journals.

Almost everything that changed in the astronauts returned to normal after the crash on Earth. None of the changes appeared to constitute a warning to future space travelers. But the findings also highlighted how little medical researchers know.

Christopher Mason, a professor of genomics, physiology and biophysics at Weill Cornell Medicine in New York City and one of the leaders of the research, called the collection of documents and data “the most in-depth examination we've ever done on a crew” as he spoke Monday during a news conference.

The four astronauts embarked on a mission, known as Inspiration4, which was the first trip to orbit in which none of the crew members were professional astronauts. Jared Isaacman, a billionaire entrepreneur, led the mission. Instead of bringing friends, he recruited three travelers who represented a broader segment of society: Hayley Arceneaux, a physician assistant who survived cancer during her childhood; Sian Proctor, a university professor who teaches geoscience; and Christopher Sembroski, an engineer.

Inspiration4 crew members agreed to participate in medical experiments – collecting samples of blood, urine, feces and saliva during the flight – and to allow the data to be cataloged in an online archive known as the Space Omics and Medical Atlas, or SOMA , which is publicly available.

While the data is anonymous, this doesn't provide much privacy because there were only four crew members on Inspiration4. “You could probably figure out who is who, actually,” Dr. Proctor said in an interview.

But he added: “I feel like there's more good than bad that comes from me being able to share my information and science progressing and learning.”

SOMA also includes data from other people who have flown on private space missions, as well as from Japanese astronauts who have flown on the International Space Station, and a study that compared the health of Scott Kelly, a NASA astronaut who lived on the International Space Station for 340 days in 2015 and 2016, with his twin brother Mark, a retired astronaut who is now a senator representing Arizona.

With more and more private citizens purchasing space travel, the hope is that SOMA will quickly fill with more information about a broader range of people than the older white men selected to become astronauts in the early decades of the era space. This could lead to treatments tailored for individual astronauts to combat the effects of spaceflight.

The wealth of information has also allowed scientists to compare short-term effects with what happens during longer missions.

During his year in space, age markers in his DNA known as telomeres lengthened, suggesting, surprisingly, that he had become biologically younger. But most of the telomeres returned to their previous size after he returned to Earth, although some became even shorter than before he left. Scientists interpreted this as a sign of accelerated aging.

The telomeres of all four Inspiration4 astronauts also lengthened and then shortened, indicating that the changes occur in all astronauts and that they occur rapidly.

“A remarkable discovery in many ways,” said Susan Bailey, a professor of radiation cancer biology and oncology at Colorado State University who led the telomere research.

Cells use RNA, a string of single-stranded nucleic acids that translates blueprints encoded in DNA into the production of proteins. Dr Bailey said the RNA corresponding to telomeres also changed in astronauts and that similar changes were seen in people climbing Everest.

“That's a strange connection,” he said.

This suggests that the cause of the growth and contraction of telomeres is not the absence of gravity, but rather the radiation bombardment that people experience at high altitudes and in space.

This was not the only effect of spaceflight.

Afshin Beheshti of the Blue Marble Space Institute of Science and NASA Ames Research Center in California pointed to molecular changes in astronauts' kidneys that could portend the formation of kidney stones. This would not pose a problem during a three-day space journey, but could become a medical crisis during a longer mission.

“Halfway to Mars, how will you treat him?” Dr. Beheshti said.

But now that this possibility is known, researchers could study how to prevent kidney stones or develop better ways to treat them.

Astronauts performed several tests on iPads to measure their cognitive performance in space. One test assessed so-called psychomotor alertness, a measure of the ability to concentrate on a task and maintain attention. The astronaut stared at a box on the screen. Suddenly a stopwatch appeared inside the box, counting the time until a button was pressed.

If the response was too slow, exceeding 355 milliseconds, it was considered a loss of attention. On average, performance in space decreased compared to when Inspiration4 astronauts performed the same test on the ground. Other tests indicate deficits in visual search and working memory.

“Our cognitive performance was not affected in space, but our response speed was slower,” Arcenaux said in an email. “That surprised me.”

But Dr Proctor said there may not have been a real difference in their ability to carry out tasks in space, just that they may have been distracted. “It's not because you don't have the ability to do better on the test,” he said. “It's just because you look up for a minute and there's Earth outside the window and you're like, 'Whoa.'”

One benefit of collecting all the data is to look for connections between changes, something that was difficult for scientists to do with earlier, smaller datasets. “When you look at it as a whole, you start to see the pieces of the puzzle together,” Dr. Beheshti said.

This could indicate a common cause, “and therefore the countermeasures are easily more targetable,” he said.

Since returning to Earth, life for some Inspiration4 astronauts has gone back in many ways to the same way it was before they left for space. Ms. Arcenaux returned to work 12-hour shifts as a physician assistant at St. Jude Children's Research Hospital in Memphis. Dr. Proctor is still a community college professor. Mr. Sembroski, who lives near Seattle, now works as an engineer at Blue Origin, the rocket company owned by Jeff Bezos.

But Dr. Proctor is now also a science envoy for the US State Department. This week he will visit Peru and Chile, recounting his experiences in schools and universities. “Now I also have this kind of global platform where I can go and do things like inspire and help prepare the next generation,” he said.

Ms. Arcenaux said she remembers looking out at Earth from the dome window of the SpaceX Crew Dragon spacecraft on the second day of her journey.

“I feel so connected to my fellow Earthlings,” she said. “We are all one on this beautiful planet.”

As for Mr. Isaacman, he's not done with the space. He and three other non-professional astronauts will embark on a mission called Polaris Dawn, which could launch next month. During that flight, also in a SpaceX Crew Dragon capsule, Mr. Isaacman and another crew member are planning to attempt the first private spacewalk.

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