Scott Kelly, the NASA astronaut who has spent nearly a year in space, returned to earth Tuesday.

Scott Kelly Lands On Earth

Kelly was aboard the International Space Station for 340 days alongside Russian astronaut Mikhail Korniekno. As they were ushered out of the Soyuz descent capsule, which they had landed in Kazakhstan, Kelly was grateful to finally breathe in some fresh air despite the cold.

“The air feels great out here,” Kelly quipped, reported The Kansas City Star. “I have no idea why you guys are all bundled up.”

During his stay in space, Kelly had become something of a celebrity, building interest in him and in space through his prolific tweeting. Over the course of his mission, Kelly shared upwards of a thousand tweets from space, many of which contained incredible pictures of his unique view of Earth and its moon.

While Kelly’s tweets were both entertaining and informative, they were, of course, not the reason he was sent into space. The crux of his mission was to serve as a test subject for NASA’s plan to send astronauts to Mars in about 15 years. A main concern for NASA is the long-term effects of living in outer space. Throughout his trip, Kelly took his own blood, performed ultrasounds, and had his eyes checked by fellow Space Station crew members.

Since Kelly has twin brother Mark Kelly, who is also an astronaut, he was the perfect person for the job.

Scott’s the guinea pig in space and I’m the guinea pig on Earth,” Mark Kelly, who happens to be married to former Arizona congresswoman Gabriel Giffords, said on The Today Show. “We have a good sense of what it takes to fly in space for six months, but if one day we decide we want to go to Mars or some other destination in the solar system, we know what the engineering is to do that, we don’t know a lot about the human body. So Scott spending a year in space and NASA studying both of us, because we are genetically the same, that’s going to give NASA a lot of information to reach out into the solar system.”

Scott Kelly also conducted a slew of experiments while in space, including growing lettuce and zinnia flowers.

Now that he’s returned to Earth, having flown around the planet 5,440 times, Kelly plans to return to Houston. He’s now broken the record for an American astronaut with a 340-day stint in space, as well as the record for total number of days in space – 520 over four missions.

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