Today NASA’s Scott Kelly, along with two Russian cosmonauts, blasts off for the International Space Station, where they plan to spend 342 days. Kelly’s identical twin brother Mark, also a (retired) astronaut, will stay on Earth to serve as the other half of an unprecedented experiment.
Researchers at a host of universities and medical schools will be watching how Scott Kelly’s weightless lifestyle affects him differently from his Earth-bound twin. They’ll study whether it increases his risk of atherosclerosis (hardening of the arteries), distorts his perception and reasoning, or alters his gut bacteria.
And among other things, they’ll look at whether cosmic rays—radiation from deep space—might shorten his lifespan by speeding up damage to his telomeres.
Telomeres are sections of DNA found at the end of every chromosome in your body. They serve a little bit like the end caps on a copper wire that stop it from fraying. They are also thought to play a part in aging, because they get shorter each time a cell replicates and copies its DNA into a new cell. When they get too short, replication stops, making the body susceptible to decay or cancer.
Scientists expect that radiation, weightlessness, changes in diet, and other features of life on the ISS will also make Scott Kelly’s telomeres shorten more quickly than his brother’s. Effectively, he’ll age faster. Just how much faster is hard to quantify—methods for estimating someone’s age from their telomeres are only just being developed. But comparing the twins’ telomeres (and their production of telomerase, an enzyme that the body uses for repairing telomeres) should provide at least some clues as to how much damage life in space can do—though with only one set of twins to study, the results will be suggestive at best.