During the "
Experiment of the twins
" (Twin study), scientists collected the molecular, physiological and cognitive profiles of the two brothers. Scott Kelly spent 340 days (from 2015 to 2016) on the ISS, and his brother Mark, also an astronaut, all this time remained on Earth. The participation of two twins in the experiment was the most important condition that made it possible to exclude genetic features and focus on external factors that influence the human body during space flight.
Scott had many physical and genetic changes that were not recorded in his brother Mark Kelly. For example, during his work on the ISS, Scott lost about 7% of his body weight, while Mark, on the contrary, gained 4%.
Scott Kelly's blood pressure in space decreased, but due to the load, the walls of the vessels became thicker (such changes are characteristic of atherosclerosis). On Earth, thickening of the walls of blood vessels is associated with high pressure and an increased risk of cardiovascular disease.
Upon returning to Earth, Scott, like many astronauts, had vision problems - scientists suggest that the blame for this is a change in pressure in the eye vessels under gravity. During a space flight, Scott was more stressed than his brother on Earth: the concentration of stress (pro-inflammatory) markers in Scott's blood was higher. However, the overall activity of the immune system was approximately the same.
During Scott’s orbit, the average length of telomeres, markers of the aging of the body, increased by about 14.5%.
Most of the changes that occurred during space flight disappeared after returning to Earth: genes began to work as before, vision returned to normal, telomeres shortened, pressure stabilized. Nevertheless, the long-term consequences of being in space are still unknown, and before sending the first people to Mars, NASA researchers will have to conduct even more ambitious experiments to identify - as far as possible in principle - all the risks.