In 2016, astronaut Scott Kelly returned to Earth after spending a year aboard the International Space Station (ISS). Meanwhile, Scott’s identical twin brother, Mark Kelly, who is a retired astronaut, remained on Earth.
We have read it and seen it before in science fiction books/films how people in space ages slower than the people on Earth due to time dilation and other factors. If another twin spends a year in space, travelling at the speed of light, the other twin on Earth may have lived fifty or so years, aging faster than the other twin. Such a speculation is yet to be studied in the future but NASA has conducted a similar research and has currently published the results of their fascinating year-long Twins Study, in which one twin remains on Earth while the other goes to space. NASA then compares the physical and mental changes that have occured to both twins – a unique opportunity to examine the impact of extended stay in space to the human body. Twins are the perfect subjects for this kind of study as they both share almost identical genetic codes and so making a comparison is easier.
The Twins Study had ten distinct investigations, each of which focused on an aspect of the human body such as genetic expression, cardiovascular health, immune system response, and more. Six months prior to Scott’s flight, the researchers performed several tests and collected samples of blood, urine, and fecal matter from both twins. While in space, Scott collected his own samples. Nine months after he landed, the researchers continued their examinations on the twins.
Based on the results, spaceflight can indeed trigger changes in the human body. But what is interesting is that these changes disappear or reverse after a few months back on Earth. According to the study, several of the findings suggest that living in space – a microgravity environment – can do harm and damage to the DNA, can change thousands of individual genetic expression, can lengthen the telomeres (protection caps at the end of our chromosomes), thicken artery walls, modify the gut’s microbiome, and increase body inflammation.
The gene expression (or epigenetics) changed drastically as soon as Scott went out into space. Previously dormant genes related to telomere growth, collagen production, immune system response, and DNA repair were turned on. On his last six months in space, expression of the above-mentioned genes ramped up, which might have cause his telomeres to increase in length. Telomeres prevent DNA strands from degrading as we age. But back on Earth, just two days after he landed, his telomeres drastically shortened, shorter than when it was pre-flight, which might imply how spaceflight could negatively affect the DNA in the long-term. In NASA’s upcoming One-Year Mission Project, scientists are planning to carry out further telomere research to figure what causes its growth and to find a way of regulating it during spaceflight.
The Twins Study is only the beginning of a series of other spaceflight-related researches by NASA. Currently, this study has only focused on one pair of twins. Hopefully in the near future, NASA will be able to corroborate the results with other studies by examining other astronauts. What is important as of now is that this study contributes to our knowledge of how spaceflight and living in space for extended periods of time can affect the physical composition and functioning of the human body.