Northwestern University researchers studying the gut bacteria of Scott and Mark Kelly, NASA astronauts and identical twin brothers, as part of a unique human study have found that changes to certain gut “bugs” occur in space.The Northwestern team is one of 10 NASA-funded research groups studying the Kelly twins to learn how living in space for a long period of time — such as a mission to Mars — affects the human body. While Scott spent nearly a year in space, his brother, Mark, remained on Earth, as a ground-based control.