He’s back on Earth, as we all know, and the medical evaluations have begun. Astronaut Scott Kelly spent 340 days on the International Space Station while his twin brother remained home, it has given NASA the unique opportunity to contrast the effects space has on an astronaut’s body in comparison to the changes that would take place during the same time period spent on Earth. The biggest difference so far? Scott Kelly grew 2-inches taller while on the ISS, and is now designated the taller brother.
Before going to space, Scott Kelly and his twin were the same height, but nearly a year in the low gravity environment allowed Kelly to stretch out, literally. In a statement to CNN recently, NASA said, “Astronauts get taller in space as the spine elongates.”
Unfortunately, his height change is only temporary. Said Williams, “[Astronauts] return to preflight height after a short time back on Earth.” It's a unique experience, getting to grow substantially taller and spend a short while like that before slowly shrinking back down to 'normal.'
Kelly and his twin Mark are part of NASA’s ‘Twins Study’ — data from the study will help NASA better understand what kind of health changes humans face in space, and will contribute toward ways to address those issues. Things like aging and mental illness are two concerns about long-term space living, and addressing them is essential to further NASA's humans-on-Mars goal.