Scott and Mark Kelly are professional astronauts, and they are also twin brothers. And this was a splendid opportunity for NASA to test many hypotheses about the effects of space on the human body. Since the brothers’ training and condition were identical, one was left on Earth and the other was sent into space for 340 days. And at the end of the experiment, the difference between the brothers turned out to be huge!

Scott Kelly had been in orbit for almost a year and returned as a grown-up. He was 5 centimeters taller than his brother Mark, who had also been in space, but for only 54 days. Scott is larger and looks somewhat younger than his 53-year-old brother.
But these are external changes, scientists were more interested in internal processes. And it turned out that space changed Scott at the cellular level and even affected his DNA! However, immediately after his return, most of the processes were reversed.

In a normal human, telomeres, the end sections of chromosomes, get shorter with age, which is a sign of aging. But Scott’s telomeres got longer after his space voyage! Does this mean that the man has started to get younger? There is no answer yet – scientists are still trying to understand this phenomenon.