Idenitcal twins Scott, right, and Mark Kelly were the test subjects for a NASA study on how long periods of spaceflight affect the human body, with Mark on Earth while Scott spent almost a year in the ...

During a recent visit to Houston, Mark Kelly was drained of 20 tubes of blood and spent several hours in an MRI machine. He was scanned while lying down, standing up and on an incline. When he was in ...

Twin brothers and former NASA astronauts Mark and Scott Kelly have each flown four missions and were part of NASA's twin study to research the impact of spaceflight on the human body. Hours before ...

Traveling to space is brutal on the body. NASA’s pioneering study of the identical twin astronauts Mark and Scott Kelly tracked signals of aging in both men while Mark remained on Earth and Scott ...

For 340 days, Scott Kelly circled the Earth aboard the International Space Station, gathering data about himself. He drew blood from his arms. He saved his urine. He played computer games to test his ...