Twins no longer identical after one brother's year on International Space Station

When do identical twins stop being identical? When one of them blasts into space for a year.

That’s according to the findings from the Nasa Twins Study which found that astronaut Scott Kelly’s genes had altered after he spent just under a year on the International Space Station (ISS).

Scott stayed on the ISS from March 2015 to March 2016 while his identical twin brother Mark, also an astronaut, remained on Earth.