March 28, 2018

When astronaut Scott Kelly returned to Earth from a year-long mission aboard the International Space Station (ISS) on March 1, 2016, he was a changed man. Literally. Compared to his identical twin brother, fellow astronaut Mark Kelly, there were several noticeable differences. Scott Kelly had grown about 2 inches (5 centimeters) taller in space, and his overall body mass had decreased a bit. However, National Aeronautics and Space Administration (NASA) scientists were most interested in the changes that could not be seen, changes in Kelly’s genetic makeup. And unlike his physical metamorphosis (his body soon resumed its Earthbound proportions), some changes in Kelly’s DNA seem to be permanent.

U.S. astronaut Scott Kelly poses inside the International Space Station in 2015. Kelly’s body and genetic makeup changed during his weightless year in space.

In 2015, Scott Kelly and Russian cosmonaut Mikhail Kornienko began a unique experiment to learn about the effects of long-term space travel on the human body. The pair spent 340 consecutive days on the ISS as part of a study that will help NASA scientists understand the challenges they must conquer if humans are ever to journey to Mars and beyond. Kelly and Kornienko orbited Earth more than 10,000 times speeding at 17,500 miles per hour (28,165 kilometers per hour) while floating in the weightlessness of microgravity (a condition of very low gravity). During this time, they experienced the stresses and solitude of long-term space flight and were exposed to cosmic radiation above the protective filter of Earth’s atmosphere.

NASA astronaut Scott Kelly (left) and Russian cosmonaut Mikhail Kornienko pose during training at NASA’s Johnson Space Center prior to their year in space. Credit: Bill Stafford, NASA

For experimental control, Scott’s brother Mark remained on Earth. As Scott’s identical twin brother, Mark’s genetic makeup is exactly the same as Scott’s. After Scott returned, NASA scientists studied the twin brothers. Any differences between Scott and Mark could be seen as the effects of the long-term space travel.

The growth spurt that Scott Kelly experienced in orbit turned out to be short-lived and he soon shrank back to his normal height as he returned to Earth’s gravity. But NASA scientists were surprised to find that Scott’s DNA, the genetic material that makes up his genes, was now significantly different from his twin. They found that about 7 percent of Scott’s genes, including those involved in bone formation, DNA repair, oxygen use, the immune system, and eyesight, had altered function when compared to Mark’s genes. Many of these genetic changes appear to be permanent.

NASA scientists think that Scott’s long-term mission in space altered his DNA through processes called epigenetics. Scientists have long known that environmental factors can alter how genes are expressed (how they function) in organisms through epigenetic processes. These processes are not mutations, nor are they physical changes in the DNA. Rather, the processes change how a particular gene functions. Various factors may switch a particular gene on or off or otherwise change how it is expressed. Such environmental factors include nutrition, exposure to certain chemicals, and stress. Scott and Mark remain genetically identical twins, but some of Scott’s genes are now expressed differently compared to Mark’s because of his time in space.

March 3, 2016

U.S. Astronaut Scott Kelly, who returned to Earth this week, is seen on July 2015 inside the cupola, a special module within the International Space Station that provides a wide range of views of Earth and the space station.

On March 1, United States National Aeronautics and Space Administration (NASA) astronaut Scott Kelly returned to Earth after a very long stay at the International Space Station (ISS). In fact, Kelly, along with his Russian counterpart cosmonaut Mikhail Kornienko, set a record for the longest-ever stay at the ISS, at 340 days. Kelly also set a record for longest time in space for a NASA astronaut.

An astronaut is a person who pilots a spacecraft or works in space, particularly in the space program of the United States. In Russia and the other former republics of the Soviet Union, such men and women are called cosmonauts. Astronauts and cosmonauts operate spacecraft and space stations, launch and recapture artificial satellites, and conduct scientific experiments.

Astronaut Kelly and cosmonaut Kornienko left for the ISS on March 27, 2015. They spent the better part of a year at the space station, performing scientific experiments and maintenance. There was another important component to Kelly’s mission. Over the course of the year, scientists studied how living in space affected his heart, the distribution of fluids in his body, his behavior and decision-making skills, and even his microbiome (the microbes that live in and on a plant or animal). His results were compared with those from his identical twin brother, retired NASA astronaut Mark Kelly, the husband of former Arizona congresswoman Gabrielle Giffords.

Mark Kelly’s stay on Earth during his brother’s mission will help researchers to more precisely understand what happens to the human body when it spends long periods of time in microgravity (very low gravity). For example, the Kelly Twins were the same height when Scott Kelly left one year ago. Upon his return, Scott is 2 inches (5 centimeters) taller than Mark. This effect is temporary, but it illustrates how a body may be affected by time in space. Studies on the Kelly Twins will help identify some of the health problems that astronauts traveling to Mars or living at a permanent moon base might experience. It will hopefully lead to prevention and treatment programs.

Scott Kelly now holds the records for most consecutive days (340) and most total days (522) in space by an American astronaut. Records are made to be broken, however. Astronaut Jeffrey Williams, who is scheduled to arrive at the ISS later this month, has spent a total of 362 days in space and should set the new record at 534 days by the time his mission is over. For his part, Kelly is hoping his records are broken by future astronauts going to Mars and beyond. In part due to his mission, those astronauts should know how to stay as healthy as possible while spending months in space.

Other articles from Behind the headlines

• A Long Stay in Space (March 30, 2015)
• Tim Peake Becomes First Official British Astronaut Aboard the ISS