An American astronaut is about to do what no man has done before — spend an entire year living in space.

Phil Keating reported on "Happening Now" that astronaut Scott Kelly will travel to the International Space Station today and spend a year studying the effects of micro gravity on the body. 

"Just think about what you were doing a year ago, most people can't even remember," Kelly said. "That's how long a year is."

Kelly and his twin brother, retired astronaut Mark Kelly, will be human guinea pigs.

Keating said that NASA will be comparing and contrasting what happens to their bodies and brains while one is in space and the other is on the ground.

The 51-year-old told Keating what he will miss the most while being gone.

"You do miss the weather and the seasons," Kelly shared. "But the thing you miss most are the human relationship you have with your friends and family and people you love on the ground."

Kelly won't be alone in space. Russian cosmonaut Mikhail Kornienki will also be living on the ISS for a year. 

This one-year mission is twice as long as typical U.S. missions to space. 

Keating said the landmark study will help enable humans to travel to Mars and beyond in the future.

Watch the video above.