NASA is conducting an experiment to determine the effects of living in space on the human body. Such studies have been done before, but this one is unprecedented in the length of time the subject will spend in space (a full 365 days) and in that the participants are identical twins.

One astronaut named Scott Kelly has agreed to live in the International Space Station for a full year while his identical twin brother, Mark Kelly, has agreed to take part from  the ground. Both brothers will undergo physical and psychological testing before and after Scott’s trip, and both will follow similar diets. Because the brothers share the same DNA, any changes that occur between them will likely have been caused by their environment.

This study is ground breaking as it will allow scientists to find ways to mitigate any problems that come with living in space for any future space trips, and may pave the way to one day travel to Mars, Venus, or even other systems entirely.