twin brothers space experiment

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1. twins

   

2. 'Space Twins' In One-Of-A-Kind Experiment

   

3. Nasa's twin study reveals something very, very strange happens to your genes in space

   

4. Identical twin brother astronauts separated in pioneering NASA experiment

   

5. What happened when one twin went to space and the other stayed home?

   

6. Astronaut Twin Study Shows How Hard Space Is on the Body