Nasa astronaut Scott Kelly returns to Earth: What a year in space does to a person’s body

Scientists are about to learn exactly what spending a year in space does to a person, after two astronauts returned from a 340 day trip to the International Space Station.

Commander Scott Kelly will be of particular interest to Nasa scientists — his identical twin, Mark, stayed on the Earth. That means scientists can compare the two and see exactly what sort of changes happen after a year in space.

Some of those findings have already emerged: Nasa has said that Scott Kelly is now two inches taller than his brother. The weightlessness of space is thought to have pulled out Commander Kelly’s spine — which means that his extra height will gradually disappear.

All of the information learnt as scientists study the effects further will go towards the eventual mission to Mars — where astronauts will have to spend even longer in microgravity and confined spaces.

But scientists already know many of the dangers and difficulties that spending so long in the International Space Station can cause. Astronauts usually stay on the station for four or five months, in which time their bodies undergo huge changes.

The most significant is the ways that the lack of gravity — and, largely of resistance — can impede the ways that the body usually keeps itself strong. That means that the bones and muscles in particular can become much weaker, an effect that can become dangerous for people once they make their way back onto Earth.

Bones will become much more brittle during time spent in space, for instance. Since the bones aren’t having to take the same kind of weight, they gradually break down and become more weak — that in turn can be dangerous since the body releases calcium to counteract it, which can potentially lead to kidney stones or broken bones.

A similar effect can happen to the muscles in the body. Because they’re not being used as much, they can also become much weaker — in doing so potentially leading to injuries when those mucsles come to be needed.

Gravity has other, more direct effects, too. The blood tends to flow more around the upper body and make the head puffier, for instance, and the heart doesn’t have to work as hard to push it around so that it can become smaller.

And the dangers are not just related to gravity, either. Being outside of the Earth’s atmosphere increases the exposure to radiation — the effects of which on humans still isn’t fully understood.

Many of the dangerous effects of space travel could be even worse on Mars — there, the gravity is much less strong, but there will be far fewer ways of supporting people once they arrive there.