When astronaut Scott Kelly returned to earth a few days ago after being in space for 340 days, he could brag about a few other things than just being the person who has achieved the longest space flight for an American. Kelly returned to Earth taller and younger than he would have been if he’d never left. As CNN reports, Kelly came back to Earth two inches taller than he was when he left. His increased height isn’t due to bone growth, however. Being up in space where there is no gravity exerting force on the human body means that a person’s spine can stretch out by as much as three inches.
More astonishing than his growth, however, is that Kelly actually came back to Earth 8.6 milliseconds younger than he would have been had he never left, reports Quartz. The reason has to do with a phenomenon called time dilation: If two objects are moving at different speeds, time runs more quickly for the slower object. Since Kelly was moving at faster speeds on the ISS for almost a year, time ran just a bit slower for him.
But don’t expect Kelly’s physical and age changes to lead to a space health spa tourism industry in the future. His height will quickly return to what it was before he left thanks to Earth’s gravity pulling back on him now that he’s terrestrial again. As for the younger age, staying up in space for almost a year to be 8.6 milliseconds younger seems hardly worth it.