Space Twins: Genetic Science Meets Space Travel on One-Year Mission

Scott Kelly in the International Space Station
NASA astronaut Scott Kelly, before taking off for a one-year mission aboard the International Space Station. Kelly's stay will help scientists understand the impacts of long-term spaceflight on the human body. (Image credit: NASA/Bill Ingalls)

Does spaceflight affect the human body all the way down to the genetic level? And if so, can a study of those changes help protect or even select future astronauts? Scientists working on NASA's one-year mission are taking the first steps toward answering those questions.

Astronaut Scott Kelly and cosmonaut Mikhail Kornienko are living on the International Space Station for just shy of one Earth year. While they aren't the first people to live in space for that long, they are under far more scientific scrutiny than any of those to come before them. NASA has emphasized that the goal of the mission is to prepare humans for the long journey to Mars

Kelly is offering genetic scientists a particularly interesting variable to study: He has an identical twin brother, former NASA astronaut Mark Kelly, living on the ground and undergoing the same swath of tests. With Mark as a comparison, scientists collecting data on Scott say they will be able to better understand how spaceflight affects human genes. [NASA's One-Year Mission: Full Coverage]

Space twins

NASA astronaut Mark Kelly and Russian cosmonaut Mikhail Kornienko are taking the ultimate space trip: one year in space on the International Space Station. See how their epic yearlong space station mission works in this infographic. (Image credit: By Karl Tate, Infographics Artist)

For a long time, the best way to tell Mark and Scott Kelly apart was by their facial hair: Mark sported a mustache, while Scott remained clean-shaven. But on the day that Scott was scheduled to take off for a nearly year-long stay on the International Space Station, Mark showed up bare-faced. A picture of them wearing matching blue NASA coveralls and sunglasses requires a few seconds of close scrutiny to figure out who is who.

The 51-year-old brothers from West Orange, New Jersey, have also led what most people would consider remarkably similar lives, having both joined the elite club of people who have flown into space. But physiologically, the brothers are probably quite different: They've had different experiences, different diets, different injuries and illnesses, all of which have shaped their bodies in unique ways. In addition, even though they were each given an identical genetic code, environmental factors will have activated different pieces of that code throughout their lives (the study of these environmentally activated genes is known as epigenetics).

"When you're born, genes are the sheet music you get. How you play that music is the epigenetics part — it's the environment acting on the sheet music," said Michael Snyder, a genetic scientist conducting an experiment on the twins as part of the one-year mission, in an interview with "There are changes in your DNA as you go through life, so there are differences [between them], but they're pretty minor. They still started out with the same sheet music."

The goal of NASA's One-Year Mission is to give scientists the opportunity to conduct a series of physical and mental experiments on Scott Kelly and Kornienko. The pair will also undergo tests for Russian and Japanese scientists. Scott and Mark Kelly are participating in a separate series of tests that have been grouped under the name "The Twin Study."

Aging in space

Susan M. Bailey is a professor of radiological health sciences at Colorado State University and has spent years studying the health effects of space radiation on astronauts. When the one-year mission was announced, Bailey proposed an experiment to study the Kelly twins' telomeres — a bit of material at the end of each strand of DNA that protects the chromosome.

It's been understood for years that telomeres shorten as people age, and may contribute to many common signs of aging, like sagging skin and graying hair, as well as an increased risk of certain diseases. The shortening of the telomeres eventually causes the cells to stop dividing and doing the job they were designed to do.

Physical and emotional stress can also cause telomeres to shorten. So, for example, a study showed that telomeres shorten much more rapidly in mothers caring for critically ill children, compared with mothers caring for healthy children, according to Bailey.

Astronauts experience plenty of stress, starting with the physical and mental stress of taking a ride on a glorified bomb, then living in an enclosed environment with no gravity and high exposure to space radiation. Could all that stress mean that astronauts are aging faster than everyone on the ground? Or does the stress of spaceflight compare to the stress of, say, losing a loved one? Bailey said she and her colleague suspect that Scott Kelly's telomeres will shorten more rapidly than his twin brother's back on Earth. But the test is entirely blinded, so the group won't see any results until after Scott touches back down on Earth. [For Manned Deep-Space Missions, Radiation Is Biggest Hurdle]

Millions of measurements

Part of the goal of these types of experiments is to find ways to protect astronauts from harm, or find solutions to the ailments that affect them. But genetic studies in particular may also explain why some people just seem better at spaceflight than others.

Snyder is working on one of the most comprehensive genetic study ever conducted on a human in space. The director of the Center of Genomics and Personalized Medicine at Stanford University, he and his colleagues are world leaders in "omics tech," which refers to a study of a person's physiology at a molecular level. This includes study of a person's genes (genomics), proteins (proteomics), molecules in involved in cellular metabolism (metabonomics) and a handful of other categories that end in "omics." When Snyder and his team run a total –omics analysis on someone, it adds up to "many millions of measurements," he said. Then there's the challenge of interpreting the results of all those measurements, and figuring out how to use that information to better understand the health of the patient.

"We want to try to interpret what's going on with [these astronauts] biologically as they go into spaceflight, which is extremely taxing," Snyder said in an interview. "We want to see what kinds of changes occur at a level that's never been done [in astronauts] before."

When a subject signs on for the full analysis by Snyder and his team, "It's like getting an IMAX movie of your biochemical changes." For comparison, the tests that a physician typically runs during a standard physical checkup would be like "fuzzy AM radio."

On the ground, Snyder and colleagues are doing a study on 100 test subjects to see if they can find genetic indicators that would explain why some people are predisposed to develop Type II diabetes, while others are not. Snyder himself developed Type II after suffering from a specific kind of viral infection. This has been known to happen in people who, like Snyder, have some genetic trait that makes them more likely to develop the disease.

Similarly selective ailments have been seen in people who have gone to space, Snyder said. So-called "space headaches" have been reported by some astronauts during spaceflight or, according to Snyder, following a return to Earth. A genetics study might help illuminate the cause of these headaches, Snyder said, but it might also simply identify those people who are likely to develop them. Looking even further into the future, it's possible that genes could reveal the likelihood that someone has the psychological fortitude to fare well on a long-duration space mission, or how likely a person is to develop cancer after being exposed to the high levels of radiation in space.

In other words, a genetic test may one day play a large role in selecting who goes to space. This idea has been presented as speculation, but the one-year mission may mark the start of it becoming a reality.

The Kelly twins, Scott (left) and Mark, are participating in an unprecedented study of how spaceflight influences human physiology. (Image credit: NASA/Bill Ingalls)

An ideal control group

Any tests currently being done on Scott Kelly while he is in space were also done before he left and will be done after he returns. Those results serve as the experimental control — they tell scientists what Scott's body (or his genome) look like under "normal" conditions. Without those results, there is no way to say if changes in his body (or his genome) are due to spaceflight or some other factor.

But even Scott Kelly is not a perfect control for himself, because human bodies, and even human genomes, can change under "normal" circumstances. Even when Kelly stays on Earth, his body will naturally change over the course of 12 months, perhaps even on a genetic and molecular level.

"We have some idea how much people drift or change [genetically] over time, but we're still learning that. It's conceivable that people naturally drift over a year, especially those in space who are exposed to more radiation," Snyder said. Which is why Mark Kelly is particularly useful to the genetic scientists: To some degree, his body will demonstrate the level of change that Scott Kelly might experience if he had stayed on the ground.

"Some of [Scott's] changes may fall within the normal variation expected for a human, while some changes could be pretty dramatic, and those could be due to the effects of space," Snyder said.

(According to Bailey, the idea had been presented to have Mark Kelly eat the same astronaut food as his brother, because in some tests it would be beneficial to rule out diet as a variable. But astronaut food is not necessarily what most people would eat if they had a choice, and Bailey said the idea was dropped to spare Mark Kelly that culinary torture. "I guess there's only so much you can ask a person to do," she added.)

Mark and Scott Kelly are not perfectly identical, but they are "much more similar than any two astronauts we've flown before," said John B. Charles, associate manager for international collaborations of NASA's human research program.

The one-year mission, he said, is an introduction between the field of genetic science and spaceflight, and one that was made largely because of the twin brothers.

"We have essentially tapped into a whole segment of the scientific research population that has not considered doing spaceflight before, because they didn't think it was relevant to their business," he said. "But [with the twins study], they now realize that they have techniques that are beneficial to our questions, and we have an environment that may help them understand their questions in a different way, which is exactly what scientists are always looking for."

It remains to be seen just how much the Twins Study will reveal about spaceflight, or about human genetics. But Charles says it's only the beginning of what he hopes will be a long relationship between genomic science and spaceflight.

"[The twins study] is not a solution, this is a demonstration," Charles said. "We're not going to get conclusive answers, but we're looking for those areas where the answers are unexpected — to give us a direction to go on future research."

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Calla Cofield
Senior Writer

Calla Cofield joined's crew in October 2014. She enjoys writing about black holes, exploding stars, ripples in space-time, science in comic books, and all the mysteries of the cosmos. Prior to joining Calla worked as a freelance writer, with her work appearing in APS News, Symmetry magazine, Scientific American, Nature News, Physics World, and others. From 2010 to 2014 she was a producer for The Physics Central Podcast. Previously, Calla worked at the American Museum of Natural History in New York City (hands down the best office building ever) and SLAC National Accelerator Laboratory in California. Calla studied physics at the University of Massachusetts, Amherst and is originally from Sandy, Utah. In 2018, Calla left to join NASA's Jet Propulsion Laboratory media team where she oversees astronomy, physics, exoplanets and the Cold Atom Lab mission. She has been underground at three of the largest particle accelerators in the world and would really like to know what the heck dark matter is. Contact Calla via: E-Mail – Twitter