Actually, astronaut Scott Kelly's DNA did not change while he was in space

As it turns out, astronaut Scott Kelly’s DNA didn’t really change.

It was widely reported last week, that following a year-long expedition to the International Space Station — twice the length of an astronaut’s average term — Kelly’s DNA underwent a 7 percent change, making him no longer identical to his twin.

Dr. Susan Bailey, a professor at the Department of Environmental and Radiological Health Sciences at Colorado State University, is now confirming that the information is untrue.

"If 7 percent of his genes changed, not only would he not be a twin, he wouldn’t be a human," Bailey told "That is ridiculous."

Photos from Kelly's space walks:

She explained the original report came from NASA’s Twin Study, to compare what happened to Scott Kelly while he was in space, with what happened to his identical twin brother, Mark, who remained on Earth. They called it the "perfect nature versus nurture study."

In the original study, NASA discussed that Kelly’s gene expression changed while in space. While 97 percent of gene expression returned to normal immediately upon his return, 7 percent of his gene expression remained the way it had been while in space.

“It was not 7 percent of his genes or the DNA, but a very different thing, and that is the genes themselves that are expressed,” Bailey explained. “They make proteins that are the workhorses of the body. That changes, the expression of those genes change all the time, every day, in all of us. From exercise, from stress, from all kinds of different things.”

But, the study was misinterpreted.

NASA updated the statement the same afternoon major news organizations picked up on the misinformation, stating clearly, “Mark and Scott Kelly are still identical twins; Scott’s DNA did not fundamentally change,” but it was too late.

The incorrect information spread like wildfire.

“The true story isn’t near as interesting as the fake news story was,” Bailey explained. “That’s basically what happened and it just all got blown out of proportion.”

She said she is now working with NASA to continue interpreting the results of the Twins Study, one that is clearly easy to misinterpret.

Although the story became quickly misconstrued, Bailey said that on the bright side, it demonstrated that the public is eager to learn more about what happens in space.

“And, it would be a very bad thing if he came back, you know, some kind of mutant,” Bailey joked.


Here's What Scott Kelly Did During His Year in Space

Welcome Home Scott Kelly! Here's What's New on Earth

Astronaut Scott Kelly Watched the Super Bowl From Space: 'No One Showed Up to My Party'