Today at 3:42 EDT, NASA astronaut Scott Kelly and Russian cosmonauts Mikhail Kornienko and Gennady Padalka launched aboard a Soyuz spacecraft to the International Space Station. For Kelly, the launch marks the beginning of an interesting year. His twin brother Mark will serve as an Earthly reference point for NASA’s biomedical experiments using twins.

The Twin study marks a rare opportunity for NASA, run by the agency’s Human Research Program in conjunction with the Human Exploration Research Opportunities Program. It’s not all that often you have identical twin astronauts willing to submit themselves as guinea pigs for a year-long research program. The Kellys have the same DNA, so for the next year the one difference between them will be their environment, Scott in a microgravity environment in orbit while Mark remains at 1G on Earth, which means it’s the first time NASA will have a chance to study the genetic aspects of spaceflight.

The hope is that these tests will give NASA a better understanding of the subtle changes that affect the human body in space, providing insight into how humans will fare on long duration missions. Say, a mission to Mars.

But there’s an obvious problem: the study has a sample size of one pair of twins. And while the twins are genetically identical, they have lived different lives with different levels of exercise, diets, environmental exposure, etc. They’ve also put their bodies through difference trials. Scott, a veteran of two space shuttle flights and a six-month space station mission, will have spent 540 days in orbit by the time his year-long mission ends next March. Mark served on four shuttle missions for a total of just 54 days in orbit. And most problematic is that earthbound Mark won’t be mimicking orbital Scott’s life. Mark will be living at home and going about his life as usual.

The small sample size isn’t lost on NASA, and as such the Twin Study is described as an observational one first and foremost. But that doesn’t mean there won’t be ongoing investigations. Throughout the year, the brothers will give blood, saliva, cheek swab, and stool samples for the biomedical teams to study, and they will also submit to psychological testing. And there are no defined outcomes for the investigations. It’s really just a chance to compare the differences from two genetically identical people in difference environments.

The biggest questions of the Twin Study will be regarding the molecular responses to the physical, physiological and environmental stressors associated with human spaceflight. Exactly the kinds of things future astronauts going to Mars will benefit from.

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IMAGE: NASA