MARK KELLY & LIFE IN SPACE

摘要

When astronaut Mark Kelly says, "I've spent a lot of time on Earth," it's relative. He's been to the International Space Station four times for short missions. His twin brother, Scott, is about to wrap up a full year in space, the longest stint of any U.S. astronaut. To understand how life in space affects humans, scientists are investigating how the twins' bodies now differ-information that might influence the future of long-term space exploration.