In 2016, after returning to Earth after 340 days in space, astronaut Scott Kelly found that he was suddenly two inches taller than his twin brother Mark, who is also a NASA astronaut. And now a new study reveals 7% of his DNA is different from his twin brother’s.
Scott Kelly rode aboard the International Space Station from March 2015 to March 2016. NASA researchers stated, “Scott’s telomeres (endcaps of chromosomes that shorten as one ages) actually became significantly longer in space,” adding that Kelly had hundreds of “space genes” activated by his flight which changed his “immune system, DNA repair, bone formation networks, hypoxia, and hypercapnia.”
The researchers explained, “This is thought to be from the stresses of space travel, which can cause changes in a cell’s biological pathways and ejection of DNA and RNA.”
The researchers linked space travel to oxygen deprivation stress, increased inflammation and striking nutrient shifts that affect gene expression. Some of these changes went back to normal within hours of landing on Earth. A few, however, still affected Scott six months after his return. In 2017, researchers discovered that the endcaps of Scott Kelly’s chromosomes—his telomeres—had become longer while he was in space. Further testing confirmed this change, and revealed that most of the telomeres had shortened again within just two days of his return.