After having spent nearly a year aboard the International Space Station, NASA astronaut Scott Kelly returned home feeling "pretty good" and about two inches taller than his twin brother, Mark Kelly. His new height didn't last long, though. Within two days of being grounded on Earth, he shrunk back down.
During his 340-day mission in space, Scott grew temporarily taller because his spine was able to elongate with less pressure from gravity. Now that he's back, Scott will undergo a year-long project to monitor his health. Medical researchers will look for other changes that may have happened to his body while in space.
Scott's bodily functions will then be compared to those of his identical brother, Mark, who is a former NASA astronaut. Having a better understanding of what happens to the body when it's subjected to long-term weightlessness will help NASA doctors better prepare astronauts for even longer missions, such as a trip to Mars.
In this case, comparing Scott and Mark provides a unique study because they have exactly the same DNA, meaning scientists can directly see how outer space mutates or damages one's genetic code.
"Kelly's year in space would provide critical data to researchers trying to understand how to keep astronauts healthy during long space voyages and fulfill the President's vision of putting American astronauts on Mars in the 2030s," the White House said in a statement.
NASA's "Twin Study" will look for changes in bone and muscle strength, heart size, balance issues and vision deficits. Since astronauts float around the spacecraft, rather than walk, their legs, hips and spine bear less of a load. As a result, the bones may break down and release more calcium, causing them to become brittle and weak.
The same goes for an astronaut's muscles: extended spaceflight results in less work for the legs and back, causing muscles to weaken or atrophy. And since the heart is doing less work, over time it too could decrease in size.
Furthermore, bodily fluids like our blood, urine and intestinal fluid surrounding our cells is free to redistribute about the body in zero gravity. This often causes "moon face," or that puffy-cheeked look astronauts get from fluid rushing to their head.
However, this can also lead to more serious side effects, including vision deterioration. For instance, astronauts who go to space with perfect vision often come back to Earth slightly nearsighted, in part due to the fact that an increased amount of fluid surrounding the brain exerts additional pressure on the optic nerve.
When returning to Earth, astronauts have to readjust to gravity and therefore may suffer from balance issues, as their inner ear is sensitive to gravity and therefore no longer functions properly.
In addition to bringing home a wealth of medical data, Scott also returns with the American record for both consecutive days and cumulative time (520 days) in space.
