Between 2015 and 2016, twins Scott and Mark Kelly lived as far apart from one another as humanly possible. Mark lived out his normal life on earth, playing golf and wandering the planet. Meanwhile, Scott spent a year aboard the International Space Station, 254 miles above Earth. Now, a suite of tests conducted on the Kelly kids, described in a Science paper on Thursday, are setting the stage for the future of space medicine.

"The paper is the beginning of the era of human genomics in space."

Scott and Mark are identical twins, which means they have identical genes, making them the perfect subjects for NASA’s twin study on the effects of living in space on gene regulation and basic physical systems as the body adapts to life in orbit. Ten different studies were conducted on the twins, the results of which are published in the new paper. For the most part, it brings good news: spaceflight may have caused short-term changes to the body, but those changes didn’t last.

In a press conference on Tuesday, scientists cautioned that the results should not be taken as evidence that we are ready to colonize distant planets. Instead, the study laid crucial groundwork for the field of space medicine, study co-author and Johns Hopkins internal medicine expert Andrew Feinberg, Ph.D., tells Inverse.

“That’s actually what was most important about our study,” Feinberg says. “The paper is the beginning of the era of human genomics in space.”

Mark and Scott Kelly, the twins in the NASA twin experiment NASA

How the NASA Twin Study Will Take Us Into Space

Comparison of the Kellys reveals that space affects the gut microbiome, causing a shift in its bacteria. Being in space caused a small thickening of the carotid artery in Scott’s neck and changes in the way fluids shifted around inside his head, which could explain why some astronauts report having vision issues in space — a condition called Spaceflight Neuro-Occular Syndrome (SANS). Furthermore, his telomeres — protective caps on the ends of chromosomes that shorten with time — also lengthened, suggesting his rate of biological aging slowed down as well. But even those telomeres shortened once he got back to Earth.

These health factors will be areas of focus as NASA develops their human research roadmap, which outlines the different health risks that astronauts will face in space. Each risk is assigned a red, yellow or green status, Mathias Basner, Ph.D., a University of Pennsylvania chronobiologist who performs research for NASA, tells Inverse.

“Basically, they have this road map that needs to be done so we get all these in the green or yellow area before we send astronauts to Mars,” Basner says.

A “red” status means that we don’t know how to treat that condition in a certain space environment. For example, we may be able to treat SANS in low earth orbit, but NASA isn’t sure how to deal with it on longer missions. Yellow status means that NASA has some idea of how to deal with these conditions. Conditions with green status are low risk.

NASA's categorization of the risks of Spaceflight Associated Neuro-ocular Syndrome. NASA

The twin study data will hopefully help turn some of the outstanding red lights into yellow or green ones as we develop ways to treat conditions in space. One of the keys to developing these treatments, adds Feinberg, is being able to perform in-depth analysis in space, which he adds is another big takeaway from the twin study.

The Development of Space Medicine

Health-related research in space is difficult, notes Feinberg. It involves shuttling supplies back and forth to earth, and working with incredibly small amounts of blood — smaller than the amount allowed to be taken from a child at a hospital. The twin study broke ground by showing that we don’t need a ton of blood to do research, opening the door to doing analysis in space in a safe way.

“What we did work out in the twins study is the fact that samples derived in space, even in very small volumes specific for space flight, are suitable for genetic analysis,” he says.

The ability to perform genetic analysis in space, adds Stanford geneticist Michael Snyder, Ph.D., is essential. His dream for future space exploration is to be able to perform personalized genetic analysis in space in real time, so we can identify and then combat future diseases that may arise.

“The one thing about a long term mission to Mars is once you’re going out there, if something goes wrong with your health you’re going to have to try and fix it yourself,” Snyder tells Inverse. The key to fixing those things, he says, is getting the correct diagnosis with enough time to act.

"My dream is that we would be analyzing people in real time at a much higher level that we are right now."

“My dream is that we would be analyzing people in real time at a much higher level that we are right now,” he continues. “People are working on those technologies, where you might sample people’s blood and see what’s going on in terms of their heart health, their metabolic health and their stress health.”

We can perform rapid genetic analysis already, but only from the safe predictability of Earth. To test whether they could take at least some of their technologies into space, Feinberg performed some analysis aboard NASA’s “vomit comet,” a plane that simulates microgravity.

It turns out there are no issues working with the blood samples in microgravity. This is a major step forward, because it suggests that it will be possible to run tests while hurtling through space en route to Mars. However, Feinberg adds, we still have a ways to go: “The sequencing methods would have to be different than on Earth. You can’t have a big sequencer.”

Weill Cornell’s Chris Mason, Ph.D., another scientist involved with the study, has already taken a big step in this direction. In 2016, he developed a nanopore-based sequencer that was the first to perform genetic analysis aboard the international space station. Technology like that is groundbreaking for space medicine, adds Snyder, because it can help detect diseases in real time or analyze the health of space travelers so we can contain illness before it spreads throughout a future colony in deep space.

“Imagine if there were some fungus or something growing in the spacecraft. You could actually figure that out with a portable sequencer. That actually does exist now,” Snyder says.

Going Beyond Low Earth Orbit

Big plans to colonize the moon, Mars, and beyond have already been announced by private space companies and the US government. Finding the right technology to keep astronauts healthy on those missions will be key to their success, but even after the Twins study, one big question remains: What happens when we go even farther away from Earth?

Scott Kelly's habitat aboard the ISS NASA

Feinberg says that we still have no idea what will happen once we spend extended time beyond low earth orbit. Cosmic radiation at high levels is already known to damage DNA; in space, this could greatly impact future space travelers in terms of cancer risk and other health issues.

“The levels of exposure in low earth orbit are much lower than would be experienced on a Mars or even moon mission,” says Feinberg. “I don’t think we should go to Mars until we know more about the stability of the genome and epigenome outside low earth orbit, so that work should be planned to be included as early as possible in next missions.”

There’s no getting around the idea that going into deep space is risky, adds Basner. “It’s really tough and radiation is certainly one problem, and I guess at some point we’re going to have to be willing to take that risk if we want to go there in the next ten years.”

Even if it doesn’t answer the radiation question right now, the NASA twin study is a step toward figuring out how risky space really is. It’s groundbreaking in its ability to provide baseline information about the risk we take as we travel into lower Earth orbit — an important stepping stone for understanding the dangers we’ll face as we inevitably go further and further into space.