Kelly himself even tweeted about the idea that he's no longer identical twins with his brother and fellow astronaut Mark Kelly.
On Monday (March 12), we published a story about astronaut Scott Kelly returning after a year in space with big changes to his genetic code, so much so that he was no longer his brother's identical twin.
It continued: "The change related to only 7 percent of the gene expression that changed during spaceflight that had not returned to preflight after six months on Earth".
Spending a year in space not only changes your outlook, it could change some of your genes. Then, Newsweek took things even further with the headline, "NASA Twins Study Confirms Astronaut's DNA Actually Changed in Space".
'What researchers did observe are changes in gene expression, which is how your body reacts to your environment.
"While in space, S. Kelly had changes to expression in the immune system, metabolism, reactions to low oxygen, stress responses, etc".
The findings are part of the Twins Study, which seeks to explore the physical and psychological effects of space travel. To track the changes, NASA analyzed Scott Kelly's cellular function before, during, and after the mission. With this study, we've seen thousands and thousands of genes change how they are turned on and turned off.
Scott Kelly spent on year on the International Space Station. "Researchers now know that 93 percent of Scott's genes returned to normal after landing".
Scott Kelly's experience was very similar to this: his gene expression changed during spaceflight, and seven percent of his genes are still expressing the way they were in space. "I used to have an identical twin brother".
According to NASA, Johns Hopkins researcher Andy Feinberg, one of 10 investigators on the Twins Study, observed variability in patterns of methylation - the process by which genes are chemically turned on and off. Chris Mason of Weill Cornell Medicine reported epigenetic changes in five biological pathways, including those related to oxygen deprivation, DNA fix and bone formation. First, there was a significant increase in average length while he was in space, and then there was a decrease in length within about 48 hours of his landing on Earth that stabilized to almost preflight levels.
That divergence in chimp versus human DNA comes from roughly 40 million mutations in the base-pairs, or letters, that make up the genetic code, Live Science previously reported.
The agency has now confirmed that Kelly came home 5 cm (2 inches) taller than his twin - a change had resolved itself within two days of his return.
The changes occurred in Kelly's telomere - a cap of genetic material at the end of each chromosome.
Kelly's one-year mission is a scientific stepping stone to a planned three-year mission to Mars, NASA said.