Something very strange happened in the world of science news this week. A month-and-a-half-old press release, which reiterated news that was released in 2017, suddenly spawned a flurry of coverage. To make matters worse, a lot of that coverage repeated claims that range from biologically nonsensical to impossible. So if you've seen any mention of astronaut Scott Kelly's DNA this week, it's probably best if you immediately forget anything you read about it.

How did Scott Kelly's genes end up one of the hottest news stories? I really have no idea. The "news" apparently traces back to a NASA press release that came out on the last day of January. That release uses a lot of words to say that attendees of a recent workshop had agreed that preliminary findings NASA had announced a year earlier were legit. So really, the "news" here is well over a year old. Yet somehow, this release has triggered a geyser of news coverage at major outlets including CNN, USA Today, and many others.

While this would clearly be an odd situation, it wouldn't be much of a problem if most of the coverage didn't involve a horrific butchering of biology. To understand the story, we have to understand the biology—and why Scott Kelly's journey through space could tell us something about it.

DNA and genes 101

Why are people excited about Kelly's DNA? The simple answer would seem to be that he has an identical twin, who must have identical DNA, and so we have a chance to see what space does to DNA. After all, space is a high-radiation environment, and we know that radiation damages DNA.

But there's quite a bit more to it than that. First and foremost, the Kelly twins' DNA is not identical. Every time a cell divides, it typically picks up a mutation or two. Further mutations happen simply because of the stresses of life, which expose us all to some radiation and DNA-damaging chemicals, no matter how careful we are about diet and sunscreen. Over the years, the Kelly twins' cells have undoubtedly picked up collections of distinctive mutations.

As a result, the more relevant comparison (and one NASA did) is Scott's DNA before and after his time in space. That can tell us how many changes were picked up while in space. But as noted above, he would have probably picked up some mutations even if he sat here on Earth. And that's where his twin Mark, who did sit here on Earth, comes in. Mark's before and after gives us a sense of the normal background rate of mutation on Earth. Comparing that rate to Scott's tells us the important number: the degree to which this rate is elevated in the environment of low-Earth orbit.

But mutations alone don't tell the full story. Less than three percent of a person's DNA is translated into the proteins that perform the functions in our cell. So chances are good that any mutations Scott picked up would have missed his genes entirely.

But the DNA sequence of a gene isn't the only way to influence its behavior. Our environments influence gene activity all the time—our bodies change gene activity to respond to everything from hostile pathogens to the time of day. All of this happens without changes in our DNA sequences; instead, the activity is largely the product of changes in the proteins that stick to DNA and regulate nearby genes, along with the biochemical consequences of those changes. Many of these changes are transient, but some can get locked into place for the long term through feedback loops.

One of these feedback loops does involve subtle changes in DNA. Rather than changing the sequence of bases, some enzymes can generate small chemical tweaks to a base, adding an extra carbon atom or two. These changes—collectively called epigenetic changes—can then alter which proteins stick to the DNA, which will change the activity of nearby genes.

So NASA naturally also tracked gene activity and epigenetic modification of the twins' DNA. In addition, it also looked at the ends of every chromosome, where there's a structure called a telomere. Telomeres are composed of the same short DNA sequence (TTAGGG) repeated multiple times; the number of repeats responds to things like stress and diet and can influence how often a cell can divide.

Testing 1, 2, 3...

NASA found that while Scott's telomeres got longer in space, they quickly returned to their pre-space state once he returned to Earth. And while lots of genes changed activity in space, most of those returned to normal, too. But for seven percent of his genes, the changed activity levels have persisted. There were changes in the epigenetic DNA modifications, too, but these are difficult to correlate with differences in specific genes. Finally, Scott picked up a few mutations as well.

Unfortunately, lots of people who have been assigned to cover the NASA announcement 45 days after it was made haven't familiarized themselves with the underlying biology. For example, one of Denver's local TV stations announced that "93 percent of his DNA returned to normal" after his return to Earth, before going on to claim that "NASA confirmed that seven percent of his genes have remained changed and may stay that way." If 93 percent of Kelly's DNA hadn't been normal, he'd be dead. Instead, a lot of his genes (though less than the 100 percent implied here) showed changes in gene activity, all of which occurred without any changes in their underlying DNA.

LiveScience gets it wrong in its article's title, where it's announced that Scott "Has Different DNA Than His Identical Twin Brother." In reality, most of the twins' DNA remained identical, and most of the differences between them occurred prior to the trip to space. An awkward title would be forgivable if the article weren't bad as well. This one, however, says Scott's "genetic code had changed significantly." The genetic code is the system that translates DNA sequences into the amino acids of proteins; changes in this code would alter every protein in a person's body, killing them. The article goes on to claim there are hundreds of "space genes" that were altered, when really these genes are involved in things like stress and the immune system.

The coverage at Business Insider was equally sloppy, making a similar claim that space "permanently changed 7% of his DNA," which is simply false. It also perpetuates the confusion between a person's genes, which remain largely unchanged, and alterations in gene activity, which take place all the time. CNN also fell victim to the gene activity/DNA difference, referring to "the transformation of 7% of Scott's DNA." Yet another report claimed that "telomeres are involved in the repair of damaged DNA," which is simply wrong.

I'm sure it would be easy to find further confusion, but at some point I had to give up reading to keep myself from having a stress response that rivaled Kelly's.

There are plenty of lessons for journalists here. One is that it's a bad idea to rush to hit stories just because you see coverage of them elsewhere—especially in cases where the story is more than a year old. Another is that you probably shouldn't be covering stories if you don't have anyone on staff who specializes in that subject area.

But it's especially disheartening to see this level of carelessness at a time when reporting on basic facts is under attack as "fake news." If we can't get the facts right when they're as definitive as they are in science and when a 10 minute phone call to a biologist could clarify them, we are demonstrating that we shouldn't be trusted with the facts on more complicated subjects.