Astronaut Scott Kelly and cosmonaut Mikhail Kornienko returned to Earth after spending almost a year in space, landing in barren Kazakhstan.
Their Soyuz capsule parachuted on to the central Asian steppes and ended a science-rich mission at the International Space Station that began last March and was deemed a stepping stone to Mars.
It was a triumphant homecoming for the American and Russian after 340 days in space.
Mr Kelly pumped his fist as he emerged from the capsule, then gave a thumbs up. He smiled and chatted with his doctors and others, as photographers crushed around him in the freezing cold.
He said: “The air feels great out here. I have no idea why you guys are all bundled up.”
Mr Kelly, 52, and Mr Kornienko, 55, travelled in total 144 million miles through space, circled the world 5,440 times and experienced 10,880 orbital sunrises and sunsets during the longest single spaceflight by an American.
Piloting the Soyuz capsule home was the much fresher and decade younger cosmonaut Sergey Volkov, whose space station stint lasted the typical six months.
The two year-long spacemen faced a series of medical tests following touchdown. Before committing to even longer Mars missions, NASA wants to know the limits of the human body for a year, minus gravity.
As he relinquished command of the space station Monday, Mr Kelly noted that he and Mr Kornienko “have been up here for a really, really long time” and have been jokingly telling one another, “We did it!” and “We made it!”
“A year now seems longer than I thought it would be,” Mr Kelly confided a couple weeks ago.
Mr Kelly’s closest US contender trails him by 125 days. Russia continues to rule, however, when it comes to long-duration spaceflight. The world record of 438 days was set by a Russian doctor during the mid-1990s.
“A really smart person said to me one time ‘teamwork makes the dreamwork in spaceflight’, and spaceflight is the biggest team sport there is,” Mr Kelly said.
He acknowledged each of the 13 US, Russian, European and Japanese space fliers with whom he and Mr Kornienko lived during the past year. “It’s incredibly important that we all work together to make what is seemingly impossible, possible.”