On March 27, 2015, astronaut Scott Kelly lifted off from Kazakhstan to the International Space Station to begin his year in space. The reason for this long mission was for scientists to experiment on what space does on the human body. What scientists know is that bones get weaker and hearts beat less efficiently. However, more research needs to be done in order for space missions to be more resourceful.

In order to conduct a perfect experiment and verify the environmental causes of the changes, such as the physiological changes anticipated during Kelly’s stay in space, many variables must be kept constant. Scott Kelly was chosen as the perfect candidate for this experiment for a reason: he has an identical twin brother. Mark Kelly, a former astronaut, stayed on Earth while Scott stayed on the International Space Station in space.

Kelly spent his days on the Space Station tweeting beautiful views of Earth, keeping in touch with his two daughters and girlfriend, and of course his brother. When Kelly landed back in Houston, Texas on Wednesday, March 3, 2016, Jill Biden, wife of Vice President Joe Biden, greeted him back home.

While we do not yet have much data on the results of the experiement, NASA has confirmed that Kelly grew taller during his time in space. Due to zero gravity in space, human’s spines lengthen. However, it will go back to normal in a matter of days. After 340 days of living in space, Kelly finally gets to go back to normal life on Earth, while NASA keeps experimenting on him and his brother.