Scientists have long been studying the effect of space on the human body. Therefore, people traveling to the ISS are always carefully studied by specialists before and after the flight. All data is analyzed in detail for differences, short-term and acquired changes. American researchers from NASA were lucky, for the first time, identical twin brothers, Scott and Mark Kelly, agreed to take part in the Twin Study experiment in the ranks of astronauts. According to the idea, Scott went to the ISS, where he spent 340 days, and Mark remained on Earth to act as a control unit. Upon the return of Scott, experts conducted a study at the genetic level, which showed that Scott Kelly’s telomeres lengthened. Simply put, he “rejuvenated” during his stay in outer space. Telomeres are the terminal parts of chromosomes that are shortened during each division. Ultimately, this leads to cell death and aging of the body. It was assumed that under conditions of increased radiation, telomere degradation will accelerate, but they grew on Scott Kelly on the ISS. Perplexed researchers transferred the samples to another laboratory, but got the same result. During the flight, the astronaut also slowed down the DNA modification process known as methylation. Unfortunately, the elongation of Scott Kelly’s telomeres was short-lived. Upon returning to Earth, their length returned to pre-flight readings. Researchers hope to identify the causes of these changes, for which 10 more astronauts were involved in a similar study. The result of the new work will be known only in 2018. It seems that space tourists will not be able to rejuvenate during flights, although the processing of the results of the experiment with the twin brothers has not yet been completed. Perhaps travelers to the distant worlds of at least aging can be avoided.