Understanding time dilation: A year in space makes you older or younger?

How space travel and long-duration missions might change the human body, and whether those changes are permanent or reversible once astronauts return to Earth, is largely unknown

Daily life aboard the International Space Station moves fast. Really fast. Traveling at approximately 17,000 miles per hour, 300 miles above the Earth, astronauts watch 16 sunrises and sunsets every “day” while floating around in a box with a handful of people they depend on for survival.

One need look no further than Hollywood blockbusters like “The Martian,” “Gravity” and “Interstellar” for futuristic visions of life beyond Earth as we venture longer and deeper into outer space. But what about the human body’s response to real-life spaceflight – what are the health