Astronauts Mark and Scott Kelly Are Still Identical Twins, Despite What You May Have Read

Some of this week’s headlines, it turns out, vastly oversold what might happen to your genes when you spend almost a year in space.

The Hill: “NASA study: Astronaut’s DNA no longer identical to his identical twin’s after year in space.”

Time: “Scott Kelly Spent a Year in Space and Now His DNA Is Different From His Identical Twin’s.”

CNN: “Astronaut’s DNA no longer matches that of his identical twin, NASA finds.”

After a flurry of similar news coverage was widely shared this week, NASA put out a statement Thursday to set things straight: Mark Kelly and Scott Kelly are just as much twins as they were before Scott went to space.

“Scott’s DNA did not fundamentally change,” the space agency said. “What researchers did observe are changes in gene expression, which is how your body reacts to your environment. This likely is within the range for humans under stress, such as mountain climbing or scuba diving.”

It continued: “The change related to only 7 percent of the gene expression that changed during spaceflight that had not returned to preflight after six months on Earth. This change of gene expression is very minimal.”

Researchers believe there is a lot to learn from the continuing twins study, which, using multiple independent researchers, measured Scott Kelly after his 340-day trip to the International Space Station in 2015 and 2016 against his twin brother, Mark, who is a retired astronaut. Scientists hope to better understand the effects of long-term space travel in preparation for trips to Mars, and the comparison with his twin offers scientists additional context.

In January, NASA published an update on the studies, while announcing it intended to release its full findings sometime this year. That months-old update appears to have fueled this week’s rash of inaccurate stories; Kelly Humphries, a NASA spokesman, said there were no new developments this week.

“The last time we posted anything was at the end of January, and it was just confirmation that some results from a year ago had been validated,” he said.

The seventh of 10 items in the January update refers to a study, by Chris Mason of Weill Cornell Medicine, on the “genetic, epigenetic, and transcriptional dynamics of each twin.” The update was prepared because some NASA scientists were going to a conference to discuss results, Humphries said.

“Although 93% of genes’ expression returned to normal postflight, a subset of several hundred ‘space genes’ were still disrupted after return to Earth,” the update read.

That fact seemed to get twisted in popular press coverage. For example, CNN initially wrote that spending a year in space “transforms your genes” before updating on Thursday to say it “transforms your gene expression.” After substantially rewriting the story — the old version can still be read here — it said the story had been “updated with additional information from NASA.”

Some outlets, including Ars Technica, The Verge and National Geographic, spotted and combated the misinformation that had been spreading. But even the astronauts themselves were snookered.

Humphries clarified that no twins are 100 percent identical, and that “over time they tend to become less identical, just like every human being.”

“They’re still identical twins,” he said.