When NASA astronaut Scott Kelly went up to the International Space Station, he had a milestone mission to complete.
He was going to spend a year in space on board the ISS, and NASA would compare his development to his twin brother on Earth.
Scott and Mark are the first twin astronauts at NASA. Like identical twins, they share the same genome. So by running the two through the same battery of samples during the year, Scott was in orbit, they could accurately tell where prolonged stays in space can affect astronauts . This is especially helpful for when we eventually send astronauts on longer missions to Mars and beyond.
After processing the data for years, the space agency released the results today in the journal Science. One thing they found was that the physically apparent changes in Scott's body were only temporary and disappeared after some time back on Earth.
But other changes in his DNA and mental abilities can be prolonged and certainly far more worrying.
Scott, with 340 days aboard the ISS, has had the longest stay in any American room. As he himself described, there is much to contend with in the time, from radiation, to weightlessness, to a limited diet and to the cold of sleep cycle and isolation.
For the study, both Scott and Mark gathered samples of urine, blood, fecal matter, and more, almost daily, and were also exposed to the same battery of scans before and after the mission. In this case, Mark is the perfect control guard that is an identical twin that continues on Earth.
"The truly dramatic response of the human body during flight is only matched by how quickly it returned to the preflight scene when it returned to Earth," said Christopher Mason, a lecturer at Weill Cornell Medicine and one of study authors. "Scott really showed one of the best examples of human plasticity and adaptability we've ever seen."
But there are reservations for this. Despite being twins, while Scott experienced changes in space that are different from Mark, they cannot accurately determine whether they were all due to the difference in habitat. For example, Scott lost weight while Mark gained less urine and showed slight dehydration. His immune system also changed, but could jump back after receiving flu vaccines.
There were other internal changes, but it is more problematic. The blood supply to the back of Scott's eyes tended to fuse, causing swelling and parts of his retina thickened. His carotid artery also thickened, which could deepen the risk of a stroke in the future.
It is important that Scott's re-activity changed in space. About 1,400 of his genes began to behave differently in space, which could be attributed to the different demands the environment placed on his body. These also increased the longer he was on board.
When he landed, it took six months for the gene activity to return to normal, and it was only 91 percent of them. For the others who do not want to switch back, the researchers are confused about what it means. "Does that mean the immune system still freaking out on the ground?" Mason says. "No, it just means that is what it does for a while after a stressful experience. Maybe it's good."
In space, Scott also experienced about 146 millisieverts of ionizing radiation, which is the kind that can cause DNA damage equivalent to approx. 10 to 15 abdominal CT scans. It made his genome more unstable and put him at risk of cancer and other mutations in the future.
Another change that continued after landing was Scott's cognitive performance. Not only did he not perform his brother on cognitive tests after landing, but his results were also lower than on board the ISS and more before his departure.
He showed this fall for six months after he landed, and scientists are still not sure why. Was it because of gravitational changes? Cosmic radiation? Strict to live in space? No one knows.
Still, all these results give NASA a base from which to work. Technically, this was a study with a topic for one so that they could repeat this with other astronauts before they can accurately predict what changes a space traveler would go through.
"There are lots of things happening on a very, very microscopic, molecular basis, which we must understand before we send people out to colonize off the planet," says Markus Löbrich, professor at Darmstadt Technical University.