NASA stunned after comparing health of astronaut who spent 340 days in space to identical twin brother on Earth

NASA had the very unique situation of having identical twin astronauts working for the American space agency; something they used to their advantage when they sent one up to Earth and kept the other here on Earth.

Say hello to Scott and Mark Kelly, two now retired astronauts who worked for the National Aeronautics and Space Administration. Twins born back in 1964, they embarked on a career in science that took them off of the planet on numerous occasions.

Back in 2015 and 2016, NASA made the move to put Scott in space for a very particular reason, with the twin brother in orbit of the planet for almost one year. 340 days to be precise; shorter than the record held by Russian cosmonaut Valeri Polyakov.

With brother Mark remaining on Earth, Scott's return to Earth was when the experiments began.

What did NASA do?

Scott Kelly was blasted in to space alongside Russian cosmonaut Mikhail Kornienko, heading to the International Space Station.

With lift off in March 2015, the duo had one major task to hand.

"The mission’s goal was to understand how the human body reacts and adapts to the harsh environment of space," NASA said.

"During the 340 day mission, almost 400 experiments were conducted on the station."

The purpose behind this was to see if there were any health issues that could be identified and used to help reduce risks of future NASA astronauts for when space agencies move to a time beyond low Earth orbit. We're talking trips to Mars and beyond; something we know SpaceX's Elon Musk is keen on.

The Kelly twins (ROBERT MARKOWITZ/NASA/AFP via Getty Images)

How did the twin brother factor in to this?

Scott Kelly's twin brother, Mark, happened to also be an astronaut with NASA, working with the space agency as a shuttle commander.

Mark stayed on Earth during Scott's 340 days in space. Given they had an identical biological make up, NASA wanted to see how their health might have differed after one of them spent time without gravity for just more than one year.

Both men undertook a number of tests before going to space as well as during and then again, during Scott's return. We're talking blood tests; stool tests; urine and saliva testing; vision and cognitive testing; and physical exercise.

With President Barack Obama after the time spent in space (Chip Somodevilla/Getty Images)

What did NASA find when comparing the twins?

The findings were published in something called 'The Twin Study'.

Steven Platts, deputy chief scientist with NASA's Human Research Program, was amazed by what the agency found. Remarkably, Scott didn't have any major long-term health problems that could be linked to long-duration flights.

His immune system behaved pretty normal, with stress returning to normal after the landing.

There were some unusual results, such as something called telomeres being lengthened in Scott's white blood cells. Telomeres usually shorten as you get older, and serve as biomarkers for accelerated aging or other risks such as cancer or heart disease. The fact his lengthened surprised NASA.

Scott Kelly in space (NASA via Getty Images)

Overall, Platts said: "The results we've seen... show the resilience and robustness of the human body.

"We've evolved here on Earth in a one-(gravity) environment, we grow up, we train, we do everything here, and yet, when we go into space... our bodies adapt and continue to function and by and large, function extremely well.

"Changes that were seen in Scott, the vast majority of them came back to baseline in a relatively short period of time when he returned to Earth. And those that did not are markers of things we already knew were likely to happen.

"This will guide future biomedical space research and allow us to have a safer journey to and from Mars."