Right now, almost all efforts of human spaceflight seem to be focused on single goal: Mars. But exploring new worlds comes with great risk, and both scientists and ethicists worry about the problems of sending people to another planet, including the physical toll that extended periods in space might have on the human body. And they're not coming up with many solid answers: there just isn’t a lot of data on the impacts of long-haul spaceflight yet.
Enter twin brothers Mark and Scott Kelly. Both accomplished NASA astronauts, next year they will participate in a year-long experiment in which they will be subject to medical tests and monitoring—Scott on the International Space Station and Mark on the ground.
It's known that being in space can affect bone and muscle mass, and the exposure to radiation can increase the risk of cancer. The astronauts hope this experiment will also shed light on how space travel affects the immune system. In one test, NASA says, both brothers will be given a flu vaccine to see how their systems react.
While there are a number of possible health issues associated with being in space, Scott will also be exercising a lot while he's up there (and that might encourage Mark, who is now retired, to run an extra mile or two in the meantime).
While there are limitations to twin studies, twins are still a lot more alike than two other random people, even two astronauts, so the ability to study the Kelly brothers should still yield some very interesting insights into how space travel affects the body.