NASA Confirms: Living Aboard The International Space Station Changed Scott Kelly’s DNA

Although it is almost a given that the DNA that we are all born with does not change throughout our lives, there is new evidence that could go against that belief as astronaut Scott Kelly’s DNA changed after spending time in space.

U.S. astronaut Scott Kelly recently spent a whole year of his life living in space. He was aboard the ISS (International Space Station) for 340 days. When he returned to Earth, many things about him had changed biologically.


For example, even though he was obviously already an adult when he went on his space mission, he grew about 2 inches taller in the year he spent off Earth.

But not only that, his body mass had also been altered suffering a noticeable decrease. And his gut bacteria had also become completely different. But more shocking than all that is that NASA scientists found that his genetic code had also been altered significantly in the time that Scott Kelly spent in space.

Sometime after his return to Earth, Scott Kelly shrunk back to his normal height losing those extra two inches he had gained but, as we will see, other changes have proved to be longer lasting.

Scott Kelly and his Twin

Something that made those changes in Scott Kelly so immediately noticeable is that he has a twin brother: Mark Kelly.


As identical twins, Scott and Mark, share the same DNA. Or, at least, they did before Scott went out to space.

Having a twin brother has helped NASA researchers to see clearly how being in space had had an impact on the astronaut’s DNA.

NASA is an engine of innovation and inspiration as well as the world’s premier space exploration agency, and we are well served by politicians working to keep it that way, instead of turning it into a mere jobs program, or worse, cutting its budget. – Billy Nye

According to a statement issued by NASA, the year that Scott Kelly spent in space altered his immune system, his bodily processes, his eyesight, and even his bone formation.

But the fact that the Kelly brothers are twins is not a coincidence. The reason why Scott spent almost a year on the International Space Station as part of the so-called Twins Study. This was a NASA project whose aim was to research the possible long-term effects of space travel, both on the human mind and the body.


As part of the Twin Study, Scott Kelly was sent up to the ISS in March of 2015 and, while most astronauts only spend about six months at the station, he remained there for almost double that amount of time.

Meanwhile, as part of this unique experiment his twin brother Mark Kelly (himself a retired astronaut) stayed on Earth. This is the first time that NASA has conducted a project involving identical twins. The reason why they wanted identical twins is that they are the only people who are born with the exact same DNA. So, using a set of twins is perfect for comparing any changes in DNA because they provide researchers with, effectively, a before and after sample.

In order for this project to work, both twins had to be examined before Scott flew up to the station. And then during the year, Scott spent in space and after he got back on Earth, NASA scientists continue to examine him.

Why Did the Astronaut Change?

When Scott Kelly came back to earth, the most noticeable change his body had gone through was that he was 2 inches taller. NASA researchers have explained this change as a result of being in an environment that is both low on oxygen and gravity.

But how about the other changes? Not only did Scott grow two inches taller, but there were also other transformations in his bone formation and his immune system. And those remained even after Scott’s return to Earth.

According to NASA researchers, all of those changes were the result of space stress. This is an unusual type of stress because it can only happen in space.

According to an article about this research published by the Business Insider, about 7% of Scott Kelly’s gene has remained changed even after his return to Earth, even though he came back over two years ago. This means that his DNA is no longer identical to that of his brother, a unique case in twins.

In his interview with the Business Insider, Christopher Mason, who was one of the leading researchers in the project, claimed that the changes to Scott Kelly’s DNA are a result of what his body perceived as a threat all the while he was in space. Kelly’s body had to adapt itself to a threatening and hostile environment for which it was not originally designed. So, all the changes are due to the body attempting to respond to this unique stress.

What Did The Study Find?

We do not know yet everything that NASA researchers have found it about DNA and the long-term effects on the human body and mind of living in space because the full results have not been released yet.

But there are a few findings that they have already shared. So, we know that some of the effects of living in space long term include the following:

  • A stretching of the spine (i.e., growing taller).
  • Muscle shrinkage due to lack of gravity.
  • Changes in the sleep cycle.

In the specific case of Scott Kelly, NASA researchers have revealed that his telomeres (the caps on the chromosomes) grew longer while he was in space but shrunk back to their normal size when he got to Earth. Also, his genetic expression changed (his levels of methylation both increased and decreased). There was also a change in the bacteria in Scott’s gut, but this can easily be explained by the change in diet.

But, is there a space gene? We do not know that yet for sure and it seems that that is what scientists want to find out next.



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