Astronaut twins Scott, Mark Kelly give clues to health effects of spaceflight

A new NASA study suggests that space travel does more than make you weightless, it can even change your chromosomes.

Appropriately named the Twins Study, the research looked deep into the effect galaxy travel had on astronaut Scott Kelly compared to his identical twin brother and former astronaut Mark. The twins gave NASA a unique opportunity as they share the same DNA.

The brothers shared biological samples before during and after Scott's nearly year-long foray into space last year. The entire time, Mark stayed on Earth.

The first results of a study delving into the impact space travel has on a person's body were released Monday.

• Scott, when he returned to Earth, was a full two inches taller.
• Scott's telomeres got longer, then shrunk back to normal. Scott's telomeres, or the caps at the end of chromosomes, became longer than his brother's while he was in space, but quickly returned to their normal length once he returned home
• The twins hosted different gut bacteria. Scott and Mark hosted different gut bacteria, or the "bugs" that aid in digestion, throughout the year-long study. This was probably a result of their different diets and environments, NASA writes.
• Scott's cognitive abilities in speed and accuracy slowed just slightly after the mission.
• Scott's bone formation slowed during the second half of his trip.
• The study determined a stress hormone was "low normal" throughout the trip but increased over the course of the expedition. The study said the hormone, linked to bone and muscle health, was, "likely impacted by heavy exercise countermeasures during flight."

NASA published their full results here.