NASA has yet to release the official result of its Twins study — a genetic experiment involving twin astronauts Mark and Scott Kelly to better understand the effects of long-term spaceflight on the human body. But early findings are already taking researchers by surprise, indicating that living in space drastically changes a person’s biology and even gene expression, Nature reports.

Between 2015 and 2016, Scott spent 340 consecutive days onboard the International Space Station, while his brother Mark, who is retired from NASA, stayed on Earth. The goal was to compare the physical and genetic differences between the two brothers to see how living in microgravity for an extended period of time affected Scott’s body. To figure this out, the twins took numerous biological samples before, during, and after Scott’s stay on the ISS.

“Almost everyone is reporting that we see differences.”

Since Scott and Mark are identical twins, they are practically the same genetically. But the samples they took for the experiment are revealing that Scott and Mark’s bodies have diverged, even in regards to their gene expression. “Almost everyone is reporting that we see differences,” Christopher Mason, a geneticist at Weill Cornell Medicine, said at the 2017 NASA Human Research Program Investigators' Workshop in Galveston, Texas, Nature reports.

Upon Scott’s return to Earth, researchers found that his telomeres — the protective caps on the end of DNA strands — were unexpectedly longer than Mark’s telomeres. Scott’s telomeres have since returned to the lengths they were before the ISS mission, but researchers are studying the telomeres of other astronauts to figure how living in space may have caused the caps to grow. Additionally during his time in space, Scott experienced less DNA methylation — when certain types of molecules known as methyl groups are added to DNA molecules. Meanwhile, his brother experienced an increase of DNA methylation during the same time. Researchers aren’t exactly sure why yet.

NASA is eager to learn more about the effects of extended stays in microgravity, since the space agency is currently working toward a human mission to Mars in the 2030s. And a round trip mission to the Red Planet is probably going to last upwards of a year, according to NASA, meaning people will be spending a lot of time in weightless environments. The findings of the Twins study could help NASA come up with ways of mitigating the effects of long-term space travel in the future, making deep space missions less taxing on the human body.

However, the official results of the Twins study may not be released for a while, and the Kelly brothers will be reviewing the data beforehand to ensure that nothing too sensitive is released. Back in March 2016, NASA said that the first peer-reviewed research from the experiment may not be released for a year or two.

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