Here’s a great article by Laura Niles at the International Space Station Program Science Office.
“Twin minds think alike” is not a common phrase in the public dialogue, but in the case of twin astronauts, it may someday become one. In a spark of astronaut, and possibly familial, curiosity, twin NASA astronauts Scott and Mark Kelly initiated an unprecedented research request to study the human effects of spaceflight using their identical twin genetic makeup. NASA’s Human Research Program (HRP) realized that another opportunity to study astronaut twins would be rare, and took the brothers up on their offer of genetic comparison in the name of human space exploration.
HRP and the National Space Biomedical Research Institute opened the Human Exploration Research Opportunities Program asking potential researchers to propose cleverly designed, but limited, short-term investigations for observational comparison between astronaut Scott Kelly and his identical twin brother, retired astronaut Mark Kelly. These pilot demonstration projects, the first of their kind, will be unique investigations into the genetic aspects of spaceflight. They will provide insight into future genetic investigations that can build on this study, but with a larger study population of unrelated astronauts.
For more information, you can read the rest of the NASA article here.
There is also a great interview with the Kelly brothers in Time magazine here.