In the debate over whether human beings should set off to other worlds beyond Earth, one of the most compelling cons is this: Our bodies don’t like it.
Few people know this better than Scott Kelly, the NASA astronaut who spent nearly a year on the International Space Station from 2015 to 2016. Like other astronauts, Kelly served as a test subject in the study of space travel’s effects on the human body. Unlike other astronauts, Kelly has an identical twin, Mark, an astronaut himself. This gave researchers an uncommon opportunity to monitor the two brothers as they lived in two very different environments—one on Earth and the other 250 miles above it.
According to their results, published Thursday in Science, Scott experienced a number of changes that Mark did not. Most of those changes went away after Scott returned to Earth. The long stint in space, the researchers say, produced some unexpected changes—but did not lead to any clinically significant health differences.
The body, sensing and reacting to weightlessness, bristles at life in space. Fluids float freely and clog the sinuses, giving faces a puffy appearance. Bones, relieved of the job of bearing weight, thin. Muscles, faced with the same, atrophy. Parts of the eyeball, for reasons scientists are still trying to pin down, become squished or swollen. And from head to toe, cells, exposed to unearthly levels of radiation, become more at risk for cancer.