One of the most simple — but important — reasons women are believed to be better space travelers is sheer size. Men, on average, weigh more than women, and firing lighter, smaller people into space requires less space and less fuel, according to National Geographic. Also, based on a 2013 study simulating survival conditions on Mars, women may require fewer calories, and therefore less food supplies. There’s also the issue of how space affects the body. For example, women who return to earth from space are more likely to faint when standing up, . and they’re also more prone to radiation-induced cancers, according to the Journal of Women’s Health. But men in space are more prone to disease, and tend to experience hearing loss more quickly. Additionally, they also suffer from vision loss more often, according to National Geographic. That last fact led NASA astronaut Scott Kelly, who has suffered from eye problems following extensive space travel, . to write in his autobiography that, “we just might have to send an all-women crew to Mars"