This week, all eyes have been on NASA astronauts Sunita Williams and Butch Wilmore, who returned home on Tuesday after nine months in space.
When they touched down in Florida, neither was able to physically step off the SpaceX Dragon capsule, and were instead carried out and placed on stretchers.
But this wasn’t due to any injury or illness; the move is merely protocol for any returning astronauts, who sometimes experience ‘space motion sickness’ as they return.
However, it will take time for their bodies to reacclimatise to life on Earth, as prolonged periods in space can lead to many physical changes.
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One of the main aspects is the effect it has on astronauts’ muscles and bone density – with a 2022 study documenting the latter in 17 ISS astronauts in missions that averaged five-and-a-half months finding that, a year after returning, they exhibited on average 2.1 percent reduced bone density of the lower leg and 1.3 percent reduced bone strength.
Helen Sharman, who was the first Briton in space, told the BBC: "It will probably take them a few months to build up their muscle mass."
But she said bone mass could take ‘a couple of years’ until it recovers – and even then, there are often ‘subtle changes in the type of bone that we do rebuild after returning to Earth that may never return to completely normal’.
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But according to NASA, there are more generalised changes we can expect.
“Imagine if all of your physiological changes were hyper accelerated so that you passed through life cycles in weeks as opposed to decades,” it said previously.
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“You’d be able to grow a beard overnight or your hair might begin graying in a matter of days or maybe menopause would come knocking by next weekend.
“This may seem like a far stretch from reality, but spaceflight causes significant physiological changes including an accelerated loss of muscle and bone density, and immune system dysfunction that parallel the effects of natural aging here on Earth.
“This makes the International Space Station (ISS) is an ideal place for scientists to conduct research on aging at a ‘space-aged’ pace.”
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A 2016 study also ‘found that spaceflight alters human hair follicle gene expression’, with the authors claiming how, in some astronauts, the genes behind the regulation of hair growth were ‘upregulated’.
This means that genes could inhibit ‘cell proliferation’ within the follicles.
Mind you, experts are also calling on people to remember simpler potential explanations behind some changes – with Emily Carney, a former US Navy nuclear technician and space historian, pointing to Williams’ greying hair.
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“A few have asked me why Sunita Williams has grey hair and looks ‘tired’ coming back home from space,” she wrote on Threads.
“This is because in space there’s no hair dye or makeup mirror at your disposal.”
Jess Hardiman