Strange but true: Astronauts grow taller in space
The human body has evolved over millions of years within the confines of gravity. Our heart, lungs, muscles, and even our DNA have all developed under the influence of the force that’s constantly keeping our feet on the ground. But what happens if gravity suddenly disappears? Ever since Russian cosmonaut Yuri Gagarin first flew into space in 1961, space agencies have been studying how microgravity and zero gravity affect the human body. Over the years, they’ve discovered that blood pressure increases, muscles atrophy, heart muscles are strained, and bone density decreases. But maybe the strangest of these biological changes is that astronauts grow about 3% taller because their spines, free from the constant pressure of gravity, slowly relax and lengthen. (After returning to Earth for a few months, astronauts shrink down to their original size.)
NASA is still learning more about the effects of space on the human body, helped in part by its yearlong Twins Study from 2015 to 2016. In the study, NASA astronaut Scott Kelly spent 340 days onboard the International Space Station while his identical twin brother, Mark Kelly, who’s also an astronaut, remained on Earth. NASA saw not only the expected changes, but also that Scott’s telomeres — caps at the end of DNA strands that help protect them — had lengthened during his stay, the opposite effect of what scientists predicted. Scott also lost some cognitive ability once he returned to Earth, perhaps as a result of his readjustment to gravity after a year in space.
Lots of things get wacky once you leave Earth — chief among them time itself. As described by Albert Einstein’s theory of special relativity, time slows down when an object (such as a space station) travels at incredibly fast speeds. This is known as time dilation. That means people (and clocks) on the Earth’s surface experience time at a slightly faster pace than astronauts on the International Space Station, who travel at about 5 miles per second. When they return to Earth, astronauts who have been aboard the ISS have made a tiny leap into the future. In 2019, after concluding the yearlong Twins Study, NASA astronaut Mark Kelly joked that while before he was only six minutes older than his twin brother Scott, who had been on the ISS for a year, he was now technically six minutes and five milliseconds older. Not exactly Doc Brown’s DeLorean, but a little bit of time travel nonetheless.
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