NASA Sent One Identical Twin Brother To Space And Studied How It Changed Him—Here Are The First Results

Last March, NASA astronaut Scott Kelly returned to Earth after spending nearly one year in space. During his 340 days aboard the International Space Station, or ISS, scientists were also observing Scott's identical twin brother, Mark Kelly, while he hung out on Earth.

Because Scott and Mark have the same DNA, scientists have had the rare opportunity to take a closer look at the changes in the human body that might be connected to spaceflight by comparing changes in Scott's genes with changes in Mark's over the same time period.

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