Astronaut Scott Kelly is now home on U.S. soil after nearly a year in space. His brother, and fellow astronaut, Mark Kelly participated with Scott in a twins experiment where the two will be compared in a number of different ways to determine how spending so long in space changed Scott. One way didn’t take too much examination to figure out – Scott grew by two inches while in space.
When unencumbered by gravity, the human body undergoes a number of changes. Muscles, no longer needed to move around or support weight, will atrophy – or grow smaller. Bones no longer need to be as strong to support body weight and will lose density. The heart no longer needs to work as hard to pump blood and will shrink. The back no longer needs to support all the upper body weight and decompresses – this is why Scott Kelly grew. Even vision can be impacted. The height component reverses quickly once back in gravity – Scott lost his new found height in only a couple days – but other effects can be long lasting.
Additionally, the radiation in orbit, outside of Earth’s protective atmosphere is much stronger – about 20 times – than it is on the surface of our planet. Long term exposure can cause a number of issues ranging from nervous system problems to cancer.
The results of the experiment in comparing Scott to his twin brother Mark will bring invaluable insight into long term exposure to space and zero g, which will help in getting humans to Mars.