NASA study of twin astronauts allowed investigation of minor changes.

Since the start of the U.S. space program, there has always been a question about how spending extended periods of time in the low or zero gravity/high radiation environment of space might impact human health.

NASA found a way to explore this question when one of two identical-twin astronauts spent nearly a year in space during 2015–2016. Scott Kelly spent 340 consecutive days on the International Space Station, while his twin brother Mark Kelly remained on Earth.

During that period, both astronauts were subjected to many different tests, with samples of their blood, urine and feces collected.

Minor changes were observed in Scott’s body, including genetic, biochemical and other changes, while he was in space. These changes largely disappeared, however, once he was back on Earth. The genetic changes included alterations in gene markers linked to stress, including DNA sequence inversions (which persisted six months after he returned to Earth) and elongation of the caps (telomeres) at the ends of his chromosomes (they shortened within 48 hours of his return to Earth).

The information, which cannot be extrapolated to all astronauts (since just two people were involved in the study) is useful for guiding future studies of astronaut health. The next step is to send three groups of ten astronauts into space for intervals of one year, six months and two to three months to study the changes that occur. This work is being accelerated in response to the Trump administration’s push to return astronauts to the Moon’s surface by 2024.