Space exploration pushes scientific understanding and innovation forward. Those who explore the depths of the universe from the relative safety of a space shuttle still put themselves at great personal risk. NASA’s Human Research Program released preliminary results of a study of astronauts and identical twins Mark and Scott Kelly to determine the effects of space travel on the human body. Scott was at the International Space Station (ISS) with Russian cosmonaut Mikhail Kornienko for the duration of the One-Year Mission. He is now retired. Mark was already retired at the time of the study.

With data gathered from the Kellys and Kornienko, NASA will fine tune the strategies they’re considering for their ultimate goal: a three-year mission to Mars. NASA catalogs five categories of risk to the human body during space travel: gravity fields, isolation/confinement, hostile/closed environments or exposure to things like microorganisms inside the spacecraft, space radiation exposure, and distance from earth.

For the “Twins Study,” NASA tested the Kelly brothers for effects on Scott’s heart, brain, muscles, and other organ systems. They also assessed Scott for changes in perception and reasoning abilities, decision making, and alertness. The role of diet and stress were considered when they looked at specific changes as well. For example, were these factors connected to the organisms found in Scott’s guts and to genetic changes in his cells? They also find out whether stress affected levels of proteins and metabolites in his biological samples.

After spending almost a year in space, the study found:

During spaceflight Scott’s telomeres were grew longer than his brother’s. When he returned home they  began to shorten to pre-flight levels again.  “That is exactly the opposite of what we thought,” Susan Bailey tells Nature.  Bailey is a radiation biologist at Colorado State University and one of the researchers working on the study. Multiple factors may have caused or influenced this, but since telomeres, sequences of DNA at the ends of chromosomes, shorten over time, this could have implications for the aging process.

While Scott showed a decline in bone formation during the second half of his trip, he also showed an increase in a hormone that is related to bone and muscle health.

The ratio between the two dominant bacterial groups in Scott’s gut was shown to have increased in flight, but returned to normal after landing.

These findings are just the beginning of a much longer story that is continuing to unfold: more evidence that it’s an exciting time to be alive.