The first preliminary findings have been announced from NASA’s Twins Study, which used the rare opportunity of having identical twin astronauts—Mark and Scott Kelly—agree to (actually it was their idea!) make “human guinea pigs” of themselves during Scott’s One-Year Mission aboard the Space Station in 2015–2016. The results comparing Mark on Earth to Scott in space show variations in nearly all physiological aspects, from gut microbes to genetic signatures.

“Almost everyone is reporting that we see differences”, said Christopher Mason, a geneticist at Weill Cornell Medical College in New York City. “The data are so fresh that some of them are still coming off the sequencing machines.”

This news comes nearly two years after the study was first reported, when it was suggested that any findings might never get published because of personal security issues over genetic information….and even now the Kellys will have final say over what information is released.

Read the rest of this story by Alexandra Witze on Nature here: Astronaut twin study hints at stress of space travel