Just over two years ago, American astronaut Scott Kelly returned to Earth after spending a year on the International Space Station. The main purpose of Kelly’s mission was to study the impact of long-term space travel on the human body. As part of this study, NASA scientists were taking advantage of the fact that he has an identical twin, former Astronaut Mark Kelly the husband of former Congresswoman Gabby Giffords who spent time on the space station himself and commanded several Space Shuttle missions during his career. Given their shared DNA and other factors, scientists hoped to be able to use what was essentially a carbon copy of their astronaut in orbit to determine the physical and other impacts that spending a year or more in space would have on humans as part of the preparation for long-term missions such as travel to Mars.

Over the year that Scott Kelly was in space, he and his brother underwent regularly scheduled testing in orbit and on Earth that was designed to aid in this process. Additionally, after Scott returned to Earth in March of 2016, he and his brother underwent further testing designed to determine how spending long periods outside the Earth’s gravity and exposed to conditions in space might impact future Astronauts. Initially, some of the effects of Scott Kelly’s time in space were interesting but not entirely surprising. For example, where Scott and Mark had been the same height when the first round of testing was conducted prior to Scott’s departure, it turned out that Scott had become slightly taller than his brother over the course of the year he was in orbit. This wasn’t really a surprise, though, since the effect had been noticed in other Astronauts who had returned after much shorter times in orbit. Over time, though, this increase in height disappeared and its believed this will happen to Scott Kelly as well. Other revelations are more intriguing, though, such as the recent report that Scott Kelly appears to have changed on a genetic level after his year in space:

Spending a year in space not only changes your outlook, it transforms your genes.

Preliminary results from NASA’s Twins Study reveal that 7% of astronaut Scott Kelly’s genes did not return to normal after his return to Earth two years ago.

The study looks at what happened to Kelly before, during and after he spent one year aboard the International Space Station through an extensive comparison with his identical twin, Mark, who remained on Earth.

NASA has learned that the formerly identical twins are no longer genetically the same.

The transformation of 7% of Scott’s DNA suggests longer-term changes in genes related to at least five biological pathways and functions.

The newest preliminary results from this unique study of Scott, now retired from NASA, were released at the 2018 Investigator’s Workshop for NASA’s Human Research Program in January. Last year, NASA published its first round of preliminary results at the 2017 Investigator’s Workshop. Overall, the 2018 findings corroborated those from 2017, with some additions.

To track physical changes caused by time in space, scientists measured Scott’s metabolites (necessary for maintaining life), cytokines (secreted by immune system cells) and proteins (workhorses within each cell) before, during and after his mission. The researchers learned that spaceflight is associated with oxygen-deprivation stress, increased inflammation and dramatic nutrient shifts that affect gene expression.

In particular, Chris Mason of Weill Cornell Medicine reported on the activation of Scott’s “space genes” while confirming the results of his separate NASA study, published last year.

To better understand the genetic dynamics of each twin, Mason and his team focused on chemical changes in RNA and DNA. Whole-genome sequencing revealed that each twin has more than expected unique mutations in his genome — in fact, hundreds.

Although 93% of Scott’s genetic expression returned to normal once he returned to Earth, a subset of several hundred “space genes” remained disrupted. Some of these mutations, found only after spaceflight, are thought to be caused by the stresses of space travel.

As genes turn on and off, change in the function of cells may occur.

Mason’s work shows that one of the most important changes to Scott’s cells was hypoxia, or a deficient amount of tissue oxygenation, probably due to a lack of oxygen and high levels of carbon dioxide. Possible damage to mitochondria, the “power plants of cells,” also occurred in Scott’s cells, as indicated by mitochondrial stress and increased levels of mitochondria in the blood.

Mason’s team also saw changes in the length of Scott’s telomeres, caps at the end of chromosomes that are considered a marker of biological aging. First, there was a significant increase in average length while he was in space, and then there was a decrease in length within about 48 hours of his landing on Earth that stabilized to nearly preflight levels. Scientists believe that these telomere changes, along with the DNA damage and DNA repair measured in Scott’s cells, were caused by both radiation and calorie restrictions.

Additionally, the team found changes in Scott’s collagen, blood clotting and bone formation due, most likely, to fluid shifts and zero gravity. The researchers discovered hyperactive immune activity as well, thought to be the result of his radically different environment: space.

What all of this means is for scientists with far more knowledge than I to consider and explain. Among the many questions that this raises, though, is whether or not these changes in Scott Kelly’s will prove to be permanent or whether, like some of the more readily apparent physical changes that occur when someone spends time in space, they will gradually disappear over time to the point where Scott is once against completely genetically identical to his brother, or at least closer than he is at this point. It’s also not clear that these genetic changes will have any real impact on Kelly’s health or life going forward. Genetic changes not unlike this are not uncommon, after all, and they usually end up being nothing all that serious. Finally, it’s unclear at this point if the changes that Scott Kelly experienced after a year in space would become more extensive for space travelers who spent a longer period away from Earth. A manned mission to Mars, for example, would likely mean that Astronauts would spend at least two years, and potentially longer, away from Earth and much of it would be on a planet that lacks the shielding from solar radiation that our planet possesses. These are obviously crucial questions that future researchers will need to look at it as we get closer to the day when we actually do send men and women on a journey to the fourth planet from the Sun.

Update: The Verge pushes back against some of the media reporting on this news and clarifies the findings of the report:

Several stories this week have proclaimed that the DNA of former NASA astronaut Scott Kelly changed during his year living on the International Space Station. The stories say that 7 percent of his genes did not return back to normal when he came back to Earth. It makes it seem as if the space environment permanently altered his genetic code. The problem? That’s not true.

The mistake stems from an inaccurate interpretation of NASA’s ongoing Twins Study. When Scott went to space in 2015, his identical twin Mark — also a former NASA astronaut — stayed on the ground. The idea was that Mark would serve as a control subject — a nearly identical genetic copy that NASA could use to figure out how the space environment changed Scott’s body.

Some fascinating results have come out of the experiment. For one thing, Scott’s gut bacteria changed significantly while he was in space. And yes, he did experience genetic changes. The protective caps on the ends of his DNA strands — known as telomeres — increased while in space. But space didn’t permenantly alter 7 percent of his DNA.

(…)

Now, the Twins Study did find that Scott and Mark had “hundreds of unique mutations in their genome,” and some of these changes were found after Scott got back to Earth, according to NASA. Bits of DNA were found circulating freely in his blood. The space agency thinks that this might have been caused by the stresses of space travel. Or it could have happened before he went to space — NASA just didn’t catch it until later. Even so, mutations in DNA aren’t that weird. “Mutation occurs all the time, as people get older,” Dan Arking, an associate professor of medicine at Johns Hopkins, who did not work on the study, tells The Verge.

What’s causing the ruckus, though, is that NASA found a shift in the way that Scott’s genes were expressed. That’s an entirely different thing than seeing a change in a person’s DNA. Gene expression refers to how active a particular piece of DNA is. DNA produces little tiny messengers of information known as mRNA, which cells use to make proteins that carry out all of your body’s basic functions. Gene expression refers to how much mRNA a gene produces. So the DNA stays the same; it’s just behaving differently.

Scientists studying Scott found that much of his gene expression changed while in space, and about 93 percent of his expression levels went back

So where did all this miscommunication come from? The stories seem to stem from a January press release from NASA about preliminary results from the ongoing Twins Study. The wording of the release isn’t very clear, and to a layperson, it does read as if 7 percent of Scott’s genes were altered by space. There’s been a huge spike in search volume for this story over the last couple of days. Additionally, both Scott and Mark tweeted out these stories, claiming that they are no longer identical twins. But that’s not the case.

“The two are still very much identical twins,” Holm wrote. “They possessed different mutations before and after the flight, and Scott experienced different changes in his RNA, not DNA. But their DNA is still nearly identical and much more similar to each other than to any other person on earth (or in space).

to normal when he got home. However, 7 percent of his genes related to the immune system, DNA repair, bone formation, and more were still a little out of whack when he returned. These genes are referred to as the “space genes,” according to NASA.

That’s still a cool result, but it doesn’t mean his genetic code is significantly different. “To have 7 percent of his gene expression changed after the spaceflight does not mean that 7 percent of the DNA changed, or that those changes were necessarily due to mutations,” Nichole Holm, a geneticist at UC Davis who did not work on the Twins Study, wrote to The Verge in an email.

(…)

So where did all this miscommunication come from? The stories seem to stem from a January press release from NASA about preliminary results from the ongoing Twins Study. The wording of the release isn’t very clear, and to a layperson, it does read as if 7 percent of Scott’s genes were altered by space. There’s been a huge spike in search volume for this story over the last couple of days. Additionally, both Scott and Mark tweeted out these stories, claiming that they are no longer identical twins. But that’s not the case.

“The two are still very much identical twins,” Holm wrote. “They possessed different mutations before and after the flight, and Scott experienced different changes in his RNA, not DNA. But their DNA is still nearly identical and much more similar to each other than to any other person on earth (or in space).

This is a crucial clarification, of course, and it certainly answers many of the questions I asked above. Additionally, it would suggest that the changes that Kelly did experience, to the extent that they can be connected directly to his time in space, are not nearly as serious as some of the news reports made them out to be. After all, as one person pointed out in a social media post I saw shortly after the original post went public, if 7% of Kelly’s DNA really did change then it technically would no longer be human and he would have less genetically in common with the rest of us than chimpanzees, which share 99% of the same DNA as humans do.

So, no, Scott Kelly is going to turn into some kind of new species and this probably doesn’t mean that there are real genetic dangers associated with long-term space travel, at least none that this study can be said to reveal.

Update #2: Ars Technica notes that this isn’t the first instance where the media has initially misreported some of the conclusions of the study involving the Kelly twins: