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Several news sites have incorrectly reported that astronaut Scott Kelly is no longer identical to his twin brother.
Retired astronauts Scott and Mark Kelly are NASA’s first and only identical twins who are part of the agency’s Twins Study program. With this project, NASA aims to get insights on the changes that happen to people who travel to space and those who remain earthbound.
For the Twins Study, Scott went aboard the International Space Station for 340 days, which is much longer than the usual six-month mission. After the mission, NASA compared the twins in several aspects.
When Scott came back, some news sites incorrectly headlined their reports saying that the twins were no longer identical. Some even cited a 7% change in Scott’s DNA. However, some experts rebutted, saying that Scott’s DNA did not change by 7%. If it had changed just by over 2%, Scott would be more different from another human being than a chimpanzee.
Experts said that the news sites mistook DNA—how genes are arranged—with gene expression, which is how genes function within the cell. In the Kellys’ case, Scott’s immune system became hyperactive compared to Mark’s because of the former’s exposure to space.
NASA plans to use studies on prolonged spaceflight, including Scott’s 340-day mission, to determine the effects of five factors—space radiation, isolation, distance from Earth, gravitational conditions, and hostile environments—on humans. The agency is compiling the data in preparation for a possible mission to Mars, which would take about three years.