Nasa twins no longer identical after space flight alters DNA
Nasa astronauts Scott Kelly and his identical twin brother Mark have shared a lot throughout their extraordinary lives.
Born just a few minutes apart, the pair were both US Navy captains, both flew on the Endeavour and Discovery space shuttles, and both spent time on board the International Space Station (ISS).
But new findings by Nasa have found that life away from planet Earth has exacted a surprising toll. The pair are no longer genetically identical twins.
After Scott Kelly (54) spent 340 days on board the ISS, experts found that 7pc of his genes no longer match those of brother Mark. Scott may even now be biologically older than his twin, scientists fear.
On learning of the change, Scott said: "What? My DNA changed by 7pc. Who knew?! I no longer have to call Mark my identical twin brother any more."
It is well known that astronauts' bodies change to adapt to living in micro-gravity, but it was generally assumed the effects wore off on returning to Earth.
However, Scott landed in March 2016, and his body has yet to return to normal. Some of the genes which appear to have changed permanently involved DNA repair, bone formation and how the cells use oxygen.
Nasa took the unique opportunity of having astronaut twins to learn more about the genetic changes of long periods in space, the first time such a study has ever been attempted.
The human body is evolved to live in Earth's gravity, and the long-term effects of space habitation are unknown. The space agency said the experiment was a "stepping stone" in its three-year mission to Mars.
While Scott was on the ISS, experts were monitoring Mark's DNA as well as Scott's so they could compare the two, a groundbreaking experiment known as The Twins Study.
"Some of the most exciting things that we've seen from looking at gene expression in space is that we really see an explosion, like fireworks taking off, as soon as the human body gets into space," said Twins Study principal investigator Dr Chris Mason, of Weill Cornell Medicine.
"With this study, we've seen thousands and thousands of genes change how they are turned on and turned off. This happens as soon as an astronaut gets into space, and some of the activity persists temporarily upon return to Earth.
"This study represents one of the most comprehensive views of human biology. It really sets the bedrock for understanding molecular risks for space travel as well as ways to potentially protect and fix those genetic changes."
Nasa measured huge amounts of data, collecting regular readings for metabolites, cytokines and proteins and discovered that spaceflight is linked to oxygen deprivation stress, increased inflammation and dramatic nutrient shifts which affect gene expression.
Overall, the results appear to show that Scott's year in space had a detrimental effect.
The researchers are now evaluating how the findings will impact future space travel beyond Earth's orbit.