When people say that space travel will change humanity, they usually mean that in a metaphorical sense. This might be a ‘Star Trek’-esque sentiment that people will have to learn to put aside our petty differences as a we explore the galaxy in peace or a broad reflection on the realities of maintaining an interplanetary civilization. But whatever the exact meaning, the point is that they don’t usually mean it literally.
When astronaut Scott Kelly returned from a 340 day mission to the International Space Station in 2016, he set a record. Most crew members stay on the ISS for about six months at a stretch. Kelly, who stayed for nearly twice as long, was sent up as part of NASA’s Twins Study, an investigation into the effects of long-term space travel. Kelly’s identical twin brother Mark, himself a retired astronaut, is also participating in the study. (In the above image of the Kelly brothers, Scott is on the left.) For his part, Mark remained on Earth as a control subject while Scott was in space.
So what sort of effects did Scott’s time in space have on him? In addition to growing two inches (he has since returned to his original height), he has also experienced a decrease in body mass and changes to his gut bacteria. So far we’re dealing with fairly typical physiological changes associated with spaceflight, albeit exacerbated by the length of his stay in orbit. Perhaps the most interesting, though, were the genetic changes that were discovered. To be clear, these are changes in gene expression (which traits are observable, or how DNA is interpreted) rather than actual changes to Scott’s genetic code itself.
All told, there have been lasting changes approximately seven percent of Scott Kelly’s genetic expression. These are largely related to things like bone formation, DNA repair, and immune response. What prompted these changes, exactly? In simple terms, they are the body’s way of responding to the physical and mental stresses associated with space travel. As Twins Study researcher Christopher Mason explains:
“Oftentimes, when the body encounters something foreign, an immune response is activated. The body thinks there’s a reason to defend itself. We know there are aspects of being in space that are not a pleasant experience, and this is the molecular manifestation of the body responding to that stress.”
NASA views Scott Kelly’s year in space and the research surrounding it as a major stepping stone toward a mission to Mars. Barring significant scientific and technological breakthroughs, the journey to Mars would require the travelers to spend three years in space.
For more details on the study and the changes to Scott Kelly’s gene expression, check out NASA’s official statement.