NASA astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko are a living experiment in what microgravity can do to the human body.
The two men completed the first six months of their 342-day stay on the International Space Station on Tuesday. This is the longest sojourn in space ever assigned to a NASA astronaut, although Russian cosmonauts have spent several missions of a year or longer on the Mir station.
Kelly and Kornienko are charting the changes to their bodies that occur in the microgravity environment of the space station, information that might help scientists back on Earth prepare for a journey to Mars one day.
Some of Kelly’s data will be compared to his identical twin brother’s, retired astronaut Mark Kelly, to see how different environments affect genetically identical men and the microbes that live in and on them.
One of the known microgravity concerns that scientists are studying is how fluids in Kelly and Kornienko’s bodies shift from their legs to their upper bodies when there’s no gravity, which can cause a buildup of pressure in the head that leads to vision problems. They’re testing a Russian device called a Chibis that can pull the blood back into the crewmembers’ legs.
Even as they’re being poked and prodded, Kornienko and Kelly have been treated to jaw-dropping sights—including 16 sunrises and sunsets a day—as the space station orbits the Earth every 90 minutes. To celebrate their six months on the station, we’ve compiled ten amazing shots from their stay so far.