(AGI) Washington, March 4 - After nearly a year of weightless suspension in space, astronaut Scott Kelly was a full 5 cm taller than his twin brother Mark. Kelly returned on Tuesday with his Russian colleagues, Mikhail Kornienko and Sergei Volkov, after 340 days in the International Space Station. In the absence of gravity, the spine has a chance to elongate. Back on Earth, gravity's pull returned the 52-year-old Kelly to the same height as his twin brother within a few hours. Though he is no longer an astronaut, Mark Kelly volunteered to take part in NASA's twins study with his brother. NASA wants to see how the identical twins measure up after a year in two very different environments: Scott in space and Mark on Earth. The study focuses on several different aspects, including the physiological, psychological, microbiological and molecular consequences of a prolonged stay in space, in view of a possible attempt to reach Mars. (AGI). .