Astronaut Scott Kelly's One-Year Mission: What's Next for NASA Twins Study

PHOTO: Expedition 46 Commander Scott Kelly of NASA smiles upon arriving at Ellington Field, March 3, 2016, in Houston, after his return to Earth. PlayJoel Kowsky/NASA via AP Photo
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The Kelly twins were reunited on Earth this week, but there's still work to be done on their pioneering NASA Twins Study, which is designed to measure the impact spending one year in space has had on an astronaut's body.

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Astronaut Scott Kelly has previously reported his vision changing in space, a likely result of fluid shifting in micro-gravity and putting pressure on his optic nerves. NASA has also revealed Kelly came back to Earth almost two inches taller.

"As soon as Scott returned to gravity and stood up, gravity began to compress his spine again. Most likely, he is already back to his pre-launch height," Dr. Shannan Moynihan, a NASA flight surgeon, said in a Reddit "Ask Me Anything" session today.

As for the bigger takeaways that could help inform a future mission to Mars, NASA scientists said today they don't have those yet and stressed that data still needs to be carefully analyzed and will take time.

"The data analysis is only now beginning in earnest," John Charles, associate manager for NASA’s Human Research Program, said at a news conference today.

Part of that process includes waiting to get some of Scott Kelly's samples returned from space. Almost half a liter of blood was drawn from Kelly during his mission, according to Charles. Some of those samples are still at the International Space Station, he said, and will return to Earth in the coming months on board the SpaceX Dragon.

This was Kelly's fourth mission, bringing his lifetime total to 520 days in space. The year-long mission was designed to measure the impact of space travel on Kelly's body.

His identical twin brother Mark Kelly served as the control subject on Earth over the past year and said he has another test tomorrow when he's scheduled to undergo a 2.5-hour MRI. Throughout the year, Mark Kelly said he came to Johnson Space Center in Houston four times, and on other occasions, NASA came to him in Arizona for tests.

The Twins Study includes ten individual investigations, including tests to measure everything from bone density to Scott Kelly's state of mind being isolated in space for so long.