NASA's latest version of Project Gemini involves actual twins.
Growing up, twin brothers Mark and Scott Kelly shared a lot -- even for twins. They took the same AP Biology class. They were co-captains of their high school swim team. They worked some of the same jobs. Even into adulthood, the brothers shared things. They both became captains in the U.S. Navy. They joined the same class at the Test Pilot School. And in 1996, they joined another class together: the 1996 class of the U.S Astronaut Corps.
Yep: Mark and Scott Kelly are brothers who are also twins who are also astronauts. They are the only twins to have been up in space together. The fact that their story hasn't yet been made into a Lifetime Original Movie is an affront to us all.
And the pair recently thought (possibly at the same time, because twins) that they should really put their twindom to use. So the twins, as twins are wont to do, schemed. And they realized that they were in a unique position to use their twindom to benefit science and humanity and space travel, all at the same time. In late 2012, NASA announced that it had selected Scott Kelly to conduct a yearlong mission, beginning in March 2015, on the International Space Station. Which would mean that Scott would be up in space for a year while Mark -- whom you might also know as the husband of Gabrielle Giffords -- would remain on Earth.
Which would present the perfect opportunity for, yes, the mother of all twin studies: one that would place two genetically identical humans in two environmentally disparate environments. One twin on Earth ... the other twin in space.