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US astronauts Butch Wilmore and Suni Williams — who have been stranded at the International Space Station for nine months for what was supposed to be a 10-day trip — are finally earthbound.
You don’t have to be a rocket scientist to realize that spending the better part of a year in outer space might have an impact on your health, but what kinds of changes can the NASA pair expect to their bodies — and could they face any long-term repercussions?
Nine months is certainly not the longest an astronaut has been in space, but Wilmore and Williams can surely expect to experience some differences, from their height to their bone density to their eyeballs.
Height
One of the more surprising effects of microgravity is that astronauts grow taller in space — sometimes by as much as two inches. Without the constant downward pull of gravity, the spinal discs expand, increasing overall height.
However, this change is temporary.
Once back on Earth, the spine compresses again, which typically returns the astronaut to their usual height. Astronaut Scott Kelly lost the nearly two inches of height that he gained during his record-breaking 340-day stay on the International Space Station after just two days back Earth-side.
Bones
Extended time in space leads to significant bone density loss.
Without the usual stress of gravity, bones — especially in weight-bearing areas like the hips and legs — begin to lose minerals, making them weaker.
According to NASA, astronauts lose between 1% and 1.5% of bone density in these areas per month while in space.
Bone density loss — also known as osteoporosis —can lead to several health complications, including increased risk of fracture and falling, reduced mobility and chronic back pain.
Muscles
Muscle atrophy is another common issue in space missions. Shenhav Shemer, a professor of biology at the Technion — Israel Institute of Technology, told Axios that muscles are likely to get progressively weaker the longer the astronaut is in space.
She added that women are generally at greater risk for both atrophy and bone loss because they naturally have less muscle mass and testosterone and may experience other hormonal changes in zero gravity — which means Wilmore and Wilson may be impacted differently.
According to NASA, astronauts have to exercise at least two hours per day on a treadmill or stationary bike to avoid the bone and muscle loss.
“Without this exercise, they would be unable to walk or stand up when they return to Earth after months of floating in space,” they wrote.
Vision
Many astronauts return to Earth with vision problems due to Spaceflight-Associated Neuro-ocular Syndrome (SANS).
While the exact cause is still being researched by scientists, one theory is that the lack of gravity alters fluid distribution in the body, leading to increased pressure on the optic nerve and changes in eye shape — eyeballs can become flattened and the optic nerve may swell, leading to reduced vision and impaired blood flow in the retina.
“Brain structural changes appear small but seem to indicate that over half of crewmembers experience one or more symptoms of SANS,” NASA wrote.
While some of these problems can persist for years, no crew member has reported significant or permanent vision loss following a mission so far.
Hearts
Because it doesn’t have to work as hard to pump blood against gravity, the heart can become slightly smaller and less efficient in microgravity.
This can lead to low blood pressure and dizziness when astronauts first return to Earth.
Research suggests this effect is temporary and some studies show astronauts generally have better cardiovascular health than the general population on Earth.
Balance
Microgravity affects the vestibular system, the inner ear structures responsible for balance.
After months of floating, astronauts may need to adjust to the shock of gravity, and feel wobbly and disoriented as a result — a phenomenon known as “space legs.”
Cancer risk
Astronauts are exposed to more radiation outside of the Earth’s protective atmosphere, thereby increasing their overall risk of cancer.
Wearing a dosimeter and other protective measures can help mitigate this risk, which NASA aims to keep no higher than 3% more than the general population.
‘The little things’
With everything that we do know, there are still things you can’t predict.
“The big things you expect, right? Being disoriented. Being dizzy,” Matthew Dominick said at a press conference after spending a lengthy stay aboard the ISS. “But the little things, like just sitting in a hard chair, right? My backside has not really sat in a hard thing for 235 days.”
“Everyone’s different. And that’s the part that you can’t predict,” Jeanette Epps, a fellow astronaut on the same mission, said.
“One issue Matt may have I may not have, but I may have several things that he doesn’t have. And so, and we did different experiments on board. So we don’t know how we’re going to respond when we, when we return and how fast. And every day is better than the day before.”
