Space Twin Study - Scott Kelly V. Mark Kelly

Space Twins - The differences

By Peter Trell

Scott Kelly (the twin who stayed in space for a year) versus Mark Kelly (the twin who stayed on Earth)

nasa astronaut scott kelly - twitter pic

We all know Scott Kelly, the NASA astronaut who spent a year in space tweeting pictures back to Earth, right? But, many of us don't know his twin brother, Mark Kelly, who was back on Earth, doing what? Not exercising, eating different things than Scott, and being a terran Earth creature. Of course, Mark Kelly's job was also an astronaut, like his twin brother Scott, of course, right!? Why would NASA not hire twin brothers, what great study material!

Here's what happened with the experiment, when Scott stayed in space 382 days while his brother Mark stayed on Earth. Here are the differences it makes to the human body to live in space: 


  • shorter telemeres (probably because Scott exercised, but we don't know) 
  • different gut bacteria (they ate different things)
  • genetic expression - methylation went crazy, which indicates how crazy the genes go when the human body transitions, in space or on earth, highlighting the stress of space travel
Is there a space gene? Maybe the twin space studies will determine it. 



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