On July 17, 1975, 229 kilometers above the earth, two orbiting spacecraft floated into a historic embrace. When the hatches between them were opened, Apollo astronaut Thomas ­Stafford greeted cosmonaut Alexey Leonov of Soyuz 19, as millions of TV viewers watched in awe. That “handshake in space,” as it came to be known, was a breathtaking act of diplomacy in the midst of the Cold War, a symbol that even the globe’s wariest antagonists could find common ground—at least in a place where there was none. Some four decades later, U.S. astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko have not only reprised that goodwill gesture, but elevated it into an opus of statesmanship. The two men returned to earth on March 2 after working side by side for 340 days in the International Space Station, a journey in which they circled the planet 5,440 times, traveled 144 million miles (nearly the distance from the earth to Mars), and conducted more than 400 scientific experiments—profoundly ­expanding our understanding of space’s effects on human ­beings and showing that, when it comes to the final frontier, there is no border between nations.

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