NASA -- In 2015, NASA set out its mission to find out how microgravity impacts the human body. Particularly, they wanted to find out how it impacts the aging of the human body. They set out twin astronauts into the mission -- one was sent out into the International Space Station (ISS) and stayed they for a year while the other twin was left here on Earth.

Scott Kelly stayed in the ISS for about 340 days gathering data not of the space but of himself. Every day, he would draw blood from his arms, measuring the size of his eyes and saving his urine. He also spent days playing computer games to test his memory as well as his ineptness to speed.

Around 240 miles below, Mr. Mark Kelly, his twin brother, who is also an astronaut of NASA is doing the same kind of tests and data collection while here on earth. Now, the team is set out to compare the data collected about these two men to learn more about how space impacts the human body. The data collected wants to unravel the mystery down to the molecular level.

On Thursday, three years after Scott Kelly did the experiment in space while his twin brother was on Earth, NASA researchers released a report that his body underwent significant changes while in the orbit. Some of the DNA in his body underwent mutation. His immune system seems to have produced a new host of some sort. On a microbiome level, his body was able to produce new bacteria while in the ISS.

Many of what seemed like harmless changes in his body disappeared when he returned to Earth. However, there were noted changes in his cognitive behavior as well as identified genetic mutations that did not seem to go back to normal when he returned. Such changes have provoked concern among scientists who conducted the study.

Some think that the changes are manageable and that there is nothing to worry about. And then there are also those who are concerned about the long journeys that astronauts plan to take to help us understand Mars and the planets beyond. The final answer will have to depend on the results of further studies about astronauts.

"I believe that it is by far the most comprehensive study of the human body to date," said Fr. Eric Topol. He is the director of the Scripps Research Translation Institute. They were not involved in the study, but they expressed their concern on the study conducted. "I don't know anything closer to the truth than this," he further said.

Although astronauts have been sent to space too many times, there are still a lot about the universe out there that remains to be a mystery to mankind. The study about the twin astronauts was published in the journal Science. It only inspired more studies of such kind to be conducted in the future.