An anonymous reader writes: U.S. astronaut Scott Kelly and Russian astronaut Mikhail Kornienko returned to Earth Wednesday after spending a year aboard the ISS, conducting experiments for future missions to Mars. Mikhail Kornienko, 55, and Scott Kelly, 52, completed the longest uninterrupted period aboard the ISS since the station was deployed in 2000. Kelly, who has made four trips to the ISS, also breaks the record for cumulative time in space by an American, with 540 days. Kelly and Kornienko performed this mission to study the biological and psychological effects of long stays in space in order to prepare for future missions to Mars in 2030 or sooner. During their stay at the station, both were frequently subjected to medical examination and a battery of tests to study the long-term effects of micro-gravity on the human body.