What are the effects of space travel on the human body?
Commander Chris Hadfield has arrived safely back on Earth after his stint on board the International Space Station - but how has five months in space affected the Canadian astronaut?
Space wreaks havoc on almost every part of the human body because there is less gravity to create the conditions we experience living on Earth.
Loss of crucial calcium
"Astronauts lose a lot of calcium essential to their bones - it's a bit like osteoporosis here on Earth," says space scientist Dr Maggie Aderin-Pocock from University College London.
Osteoporosis is a disease, where bones become more brittle, which sometimes affects older people and women - and can mean you're more likely to break bones.
It's thought that this happens in space because astronauts don't do load-bearing exercise - like walking and running, or lifting things - pulling against the Earth's gravity.
To try to avoid this, while they're in space astronauts have a special diet and have to do up to two hours of exercise per day.
Muscles and bone waste away
Even then, after five months in orbit above the Earth, an astronaut like Commander Hadfield would typically lose as much as 40% of muscle and 12% of bone mass, says Jeremy Curtis from the UK Space Agency.
"The muscle loss is the equivalent of a 20-year-old turning into a 60-year-old over a period of three months," he says.
SPACE IN NUMBERS
- 2 - the number of hours per day astronauts exercise while in space
- 40 - the percentage of your muscles you will lose after five months in space
- 365 - the number of days it takes your bones to recover
- 460 - kilometres distance between Earth and the International Space Station
The 53-year-old astronaut will experience problems standing up and balancing - and he won't be able to drive to begin with.
He'll have to undergo a special rehabilitation programme for the next year to rebuild his muscles and bones - and he may never regain his previous bone mass.
The exposure to higher levels of radiation in space also means Chris may be more likely to suffer from cancer later on in life.
But on the plus side, scientists say studying the effects of space flight on the human body can help with developing new treatments for diseases like osteoporosis and cancer here on Earth. Thanks Commander Hadfield!