NASA calls his mission a significant step toward travel to Mars. Kelly has now spent more days in space than any other American. NASA plans to study how so much time without gravity impacted his body.
After traveling 144 million miles in space, Commander Scott Kelly is on the last leg of his long journey home. He landed overnight in Kazakhstan.
"There's nothing like new cold air coming into the capsule," he said.
RELATED: Scott Kelly returns to earth after 340 days in space
Kelly answered a few questions before boarding a 20 hour flight to Houston.
"Leaving the space station was bittersweet," said Kelly. "You know, I've been there a long time so I looked forward to leaving. But at the same time it's a magnificent place and I'm going to miss it," he said.
He will reunite with his family late tonight.
Kelly says being away from those he loved was the most difficult part of life on the International Space Station.
"A year is a long time, you know?" he said. "It felt like I had been up there my whole life after about the first six months."
With the mission over, the science begins.
Once Kelly gets to Houston, NASA will spend about a year testing both Scott and his twin brother Mark to determine the effects of life with in space; comparing the twins results down to the molecular level.
"I'm definitely encouraged on our ability to go even longer," said Kelly.
That's important, because a mission to Mars will last about two and a half years.
Astronaut Scott Kelly returning home after a year in space. If it was you, what's the first thing you would do? #abc7now— Tiffany Wilson (@TWilsonTV) March 2, 2016
NASA calls Kelly's trip an important stepping stone to humans reaching the Red Planet.
"By going to Mars one day it will make things better on Earth and I'm happy to be a part of it," said Kelly.
He's expected to touch down in Houston at about 8:45 p.m.
When he gets home, Kelly says he's very excited to jump into his own pool.
For more stories about space, click here.