Twin brothers Scott and Mark Kelly presented an incredible scientific opportunity for NASA. As Scott Kelly journedy to the International Space Station, Mark Kelly remained on Earth, allow NASA to compare the effects of space on Scott Kelly’s genes after an extended period in space – and the results were mind-blowing.

NASA ran a lot of tests on the Kelly brothers after Scott returned to Earth last year. Researchers found that space travel apparently altered the process that regulates gene expression in Scott Kelly’s body, suggesting that space itself does in fact alter our genes at least somewhat.

Apparently, space travel caused an increase in what is known as methylation, which is what switches genes on and off. While it’s a normal process that happens here on Earth, it sped up when Scott Kelly was in space. NASA’s incredible video describing the research is embedded at the bottom of this post.

“Some of the most exciting things that we’ve seen from looking at gene expression in space is that we really see an explosion, like fireworks taking off, as soon as the human body gets into space,” Twins Study Principal Investigator Chris Mason, Ph.D., of Weill Cornell Medicine, said. “With this study, we’ve seen thousands and thousands of genes change how they are turned on and turned off. This happens as soon as an astronaut gets into space, and some of the activity persists temporarily upon return to Earth.”