Human beings have evolved to become "perfectly adapted to life on Earth", said Sky News. So, spending time in space, without gravity or sunlight, and exposed to radiation, "poses a real challenge, physically".
And for "stranded" astronauts Sunita "Suni" Williams and Barry "Butch" Wilmore – whose routine eight-day visit to the International Space Station turned into an unscheduled nine-month stay – the challenge may be even bigger when they finally come back home to Earth today.
The pair, travelling in a SpaceX Dragon capsule, left the ISS early this morning. After a "fast and fiery re-entry through Earth's atmosphere", they are due to splash down off the coast of Florida tonight, said the BBC. The fresh air will feel "fantastic", said Helen Sharman, Britain's first astronaut, but such an extended space mission will, said the broadcaster, have taken a "toll on the body".
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'Struggle to walk'
"You adapt incredibly quickly to being in space," Nasa astronaut Frank Rubio, who spent 371 days in space in 2023, told Time magazine last year. But readapting to life back to Earth can be "a little bit longer and more difficult". The first two or three months will be focused on recovery, "reincorporating yourself into Earth, your family, and then also rehabilitating your body".
After splashdown, the astronauts will be taken to the Johnson Space Centre in Houston, Texas, for a medical check-up. Astronauts returning from long-duration space missions "routinely exit their spacecraft on stretchers", said CNN, because their bodies "need time to adjust to feeling Earth's gravity". "The weight and the heaviness of things just is surprising," said Janette Epps, a member of a team that spent nearly eight months in space. I was lying down "any chance I got".
Nine months without gravity will have caused "significant, and irreparable, bone density loss", said The Guardian. Being in space "causes muscles to waste in your arms, legs, trunk and elsewhere, including your heart, which, because it doesn't have to pump blood against gravity, has to work much less hard". Fluids also "don't drain as easily". The returning astronauts will "struggle to walk, get dizzy easily, and have bad eyesight", because the "build-up of fluid changes the shape of their eyeballs, and weakens their vision". They may need glasses for the rest of their lives.
In space, clothing floats off your skin, so your skin gets "almost baby-like sensitivity", said Alan Duffy, an astrophysicist at Australia's Swinburne University told the paper. On Earth, some astronauts "feel like their clothing is sandpaper".
The returning pair will also have to exercise extensively: the reconditioning will be similar to the "intense physiotherapy" performed by anyone who has come out of a coma.
'Incredible connection to humanity'
These astronauts' return "is itself a research project", said Duffy, because most research on human life in space is based on missions that last less than six months.
One major concern is exposure to radiation in space. Earth's atmosphere and magnetic field shield us from high levels of radiation, which can lead to DNA damage and increased cancer risk. But little is known about how much increased exposure in space might impact astronauts in the long-term – because only about 700 people have ever been to space.
We do know, however, that, for returning space travellers, anxiety and depression are common. Seeing the Earth from space has led some astronauts to report "an incredible connection to humanity", said The Guardian, and "an immediate sense of its fragility". "Some people call it a feeling of inspiration," astrophysicist Brad Tucker, of the Australia National University, told the paper. "Some people call it feelings of inadequacy, in terms of just how big the world is."
The astronauts also have to come back down to Earth figuratively, as well as literally. "They have to make breakfast and they have to drive to work," said Tucker. "It is a huge transition from living in a very inspiring environment."
