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NASA's Twins Study

Surprising Discoveries from NASA’s Twins Study

How does a year in space change a person? That’s what NASA wanted to find out. And they had the perfect test subjects: identical twin astronauts! Here’s what  NASA’s Twins Study discovered.

A Unique Opportunity

Scott and Mark Kelly are both astronauts. They’re also identical twins, which means that they’re as close to being the same person–genetically speaking–as it’s possible to be.

While Mark remained on the ground, Scott spend almost a year on the International Space Station. That gave researchers the chance to study the effects of prolonged space travel in an unprecedented way.

10 teams worked on NASA’s Twins Study, tracking multiple variables. A total of 84 researchers at 12 universities were involved, and they discovered major changes in Scott during his year on the ISS.

Scope of the Study

The brothers first became astronauts in 1996, but at the time, no one at NASA was interested in mounting an expensive study about them. In 2013, however, Scott was chosen for an extended mission in orbit.

“When it came to the fact that I was going to spend a year in space, it was so unique that I actually thought maybe there was some merit to it,” Scott told “[I]t turns out there was some interest once people started talking about it.”

The full study began 6 months before Scott left on his mission and continued 9 months after he returned. Scientists wanted to know what changes long-term spaceflight will have on everything from our immune systems to our genetics. They also wanted to find out if those changes could be reversed.

Although preliminary results were published in 2017 and 2018, this is the first time that a fully summary paper has been available to the science-loving public.

Genetic Fireworks

Living on the International Space Station had a measurable impact on Scott Kelly’s health, all the way down to his DNA. The lack of gravity, in addition to the higher levels of radiation, lower levels of oxygen, and the disruption of circadian rhythm, caused an immediate and widespread response in the way his genes were expressed.

“Some of the most exciting things that we’ve seen from looking at gene expression in space is that we really see an explosion, like fireworks taking off, as soon as the human body gets into space,” Chris Mason, one of the lead researchers, explained.

In space, genes that had been dormant on Earth became active. His telomeres–sheaths that protect the ends of chromosomes–changed. So did genes controlling immune response. Essentially, every system was on red alert during Scott’s time in space, desperately trying to adapt to this strange, new environment.

Telomere length has been linked to aging–shorter telomeres equal more rapid signs of aging. Unfortunately, living in space might not be the fountain of youth; Scott’s telomeres shrunk again shortly after he returned to Earth.

A Long Recovery

The good news is that almost everything went back to normal. That doesn’t mean recovery was easy. “I was in space more than twice as long [as last time] — I felt more than twice as bad when I got back,” he told interviewers. He said it took about 8 months to feel normal again. Even so, he experienced thickened arteries, slower cognitive speed, and vision problems that are likely permanent.

The insights from NASA’s Twins Study will help us plan long-duration space missions in the future. Including, perhaps, spaceflight to Mars. Now that we know the effects of spending a year in space are mostly reversible, we can realistically start moving towards a future where humans travel beyond the Moon.

Deana Adams

When Deana Adams was a kid, she begged her parents for a backyard telescope every birthday and Christmas until they finally caved. As an avid amateur stargazer, she memorized the constellations and hunted for the planets, collecting facts about astronomy the way other kids collected baseball cards or Barbies.

Deana is a contributing writer at NightSkyGaze. She still has her very first telescope.