How Scott Kelly’s Body Changed in Space

Bone loss, kidney stones, skin soreness, vision problems. Returning from space isn’t an easy trip.

Pool photo by Kirill Kudryavtse

Scott Kelly, U.S. astronaut and famed Instagrammer, came back from space a changed man. Now, NASA wants to know exactly how much he has changed.

Last Friday, Kelly opened up about the physical challenges of returning to Earth in his first press conference since the end of his record-breaking 340-day stint on the International Space Station. By comparing Kelly’s postflight body to that of his identical twin brother Mark, NASA hopes to learn more about the effects of extended extraterrestrial outings on the human body.

“As some of you might know, I flew 159 days last time and when I got back I was feeling pretty good,” Kelly told press, with reference to his earlier six-month voyage. “Initially, this time, coming out of the capsule, I felt better than I did last time but at some point those two lines have crossed.”

The muscle soreness and fatigue, Kelly said, are a lot worse after spending nearly a full year in space. In space, Kelly had to spend about two hours a day exercising to keep his muscles functional for his return. One reporter asked him which muscle groups, in particular, were bothering him now that he’s back. “Most of ’em,” was the astronaut’s laconic reply.

“I think coming back to gravity is harder than leaving gravity,” said Kelly. “So, I don’t know, maybe the aliens got it a lot easier than we do.”

Most of the difficulties associated coming back to Earth are, of course, a function of gravity. NASA already knows that living in reduced gravity has a range of side effects on the human body. It causes bone loss and increases the risk of kidney stones. It shrinks muscle fibers and affects cardiac function.

Some returning astronauts have also reported developing vision problems, although NASA does not yet know the specific cause. Initial MRI results, the space agency notes, suggest that “pressure changes in the brain and spinal fluid” brought on by weightlessness could damage the optic nerve.

But one of the most serious risks of spending extended time in space has nothing to do with gravity. Exposure to space radiation outside of the Earth’s atmosphere could limit the time astronauts spend on missions to Mars.

Considering the range of risks, Kelly initially appears to be in good shape with only minor complaints.

After a year of living in microgravity, he had become an inch and a half taller due to the temporary expansion of his spine but he quickly shrunk back to his former height after touching down in Kazakhstan. As Kelly put it during Friday’s presser, “Gravity pushes you back down to size.”

And because Kelly didn’t even feel the weight of his clothing in space, his skin is now irritated just from moving around while dressed.

“[My skin] is very, very sensitive,” he said during the press conference. “It’s almost like a burning feeling wherever I sit or lie or walk.”

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“I’m kind of surprised how I do feel different physically than the last time with regards to muscle soreness and joint pain and [this] skin issue,” he added later.

But Kelly doesn’t get to take much of a vacation. His hard work as NASA’s guinea pig continues. Several times during Friday’s press conference, Kelly referenced the many medical exams he has undergone since returning home, including multiple hours spent in an MRI machine—which may be even more of a nightmare for the claustrophobic than the thought of a full year in space.

With regards to his vision, Kelly reported: “I would say it was very consistent with my last flight from a subjective point of view.” The astronaut has experienced some vision impairment after his space flights, but nothing permanent.

But Kelly won’t objectively know the toll that space took on his body until NASA scientists crunch the numbers.

“Now we’re in the phase of collecting the data and starting to analyze the data and seeing what we really learned from this mission,” said Dr. John Charles of NASA’s human research program in an earlier news briefing. (Charles told press that there were no results that could be shared at this time.)

While Kelly waits for the results of his medical tests, he can comfort himself with one bit of good news: According to astrophysicist Neil deGrasse Tyson, the astronaut actually got younger in space thanks to relativity, if only by one hundredth of a second.

But medical exams aren’t likely to explain one problem Kelly has experienced since regaining his land legs: He’s not exactly Stephen Curry.

“I tried to shoot some basketballs yesterday and I didn’t get any of them in the net,” Kelly told reporters. “Not that I’m a good basketball player in general anyway.”