What happens to your body when you spend a year weightless in space? In a unique project, NASA is about to find out, as they send two crew members into orbit for a year.

And in a special twist, they’ll be able compare the changes that astronaut Scott Kelly experiences to the changes that his twin brother Mark experiences here on Earth!

The Kelly brothers volunteered to be a part of the research, and hope that their work can help scientists not only track the effect of space vs. Earth, but use that information to help prepare the human body in general for long trips to space.

The Kellys will be 51 when the project starts. As identical twins, the brothers are nearly identical, so it will give the team at NASA a control subject to measure physical and emotional changes, and it’s especially helpful to them because both brothers are long-time astronauts with data going back to the mid-1990s. Each day, the brothers will undergo 10 tests to track medical and psychological fluctuations.

Joining Scott Kelly on the flight is Russian Cosmonaut Mikhail Kornienko.

Their mission begins in March 2015. Learn more at NASA’s One Year Crew page.