(TIME) — We finally learned what a year in space did to astronaut Scott Kelly's body — and the results have major consequences for human spaceflight.
The medical results of astronaut Scott Kelly's year in space have been revealed, underscoring the consequences of prolonged time off-world.
One of the things that made Kelly an improbably perfect specimen for the year-in-space study was that he has an identical twin brother, Mark Kelly. Both were NASA astronauts, both are generally fit and healthy and both, of course, share the same basic genome. Take two people with identical genetic software and put them in decidedly non-identical surroundings, and then compare them throughout the year and after. At least some of the differences in health will be attributable to the time spent one of them spent in space.
The results are mixed — Kelly fared better than expected on some measures and worse on others. The overall conclusion is less ambiguous: space travel is exceedingly hard on the human body, and we have a lot to learn before we’re ready to start living on the moon or Mars.