Scott and Mark Kelly: twins who became subjects of a groundbreaking space biology experiment

Twin astronauts Scott and Mark Kelly in blue NASA flight suits against ISS backdrop — central figures of the 'Twin Study' space experiment

The image shows twin astronauts Scott and Mark Kelly in official NASA flight jackets adorned with mission patches. Scott spent a year aboard the ISS while Mark remained on Earth, enabling scientists to study the physiological and genetic effects of long-duration spaceflight.

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