NASA astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko returned to Earth Tuesday night after spending 340 days living in space on the International Space Station.
Kelly, 52, and Kornienko, 55, along with cosmonaut Sergey Volkov landed in Kazakhstan at 11:30 p.m.
The pair traveled 144 million miles through space, circled the world 5,440 times and experienced 10,880 orbital sunrises and sunsets.
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The 340 day spacemen will undergo 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.
Scientists are hoping for more one-year subjects as NASA gears up for human expeditions to Mars in the 2030s. Radiation will be a top challenge, along with the body and mind's durability on what will be a 2½-year journey round trip.
Kelly will head to Houston with two flight surgeons and several other NASA reps, and is scheduled to arrive late Wednesday night at the Johnson Space Center where he will be reunited with his two daughters, ages 21 and 12; his girlfriend, a NASA public affairs representative, and his his twin brother and fellow astronaut, Mark Kelly who remained on Earth and participated in the same study.
Kornienko returned to his home in Star City, Russia, near Moscow, to his wife, daughter and toddler grandson.
The six Expedition 46 crew members gather one last time before saying farewell and closing the hatches between the Soyuz spacecraft and the International Space Station, Tuesday, March 1, 2016. (L-R) Yuri Malenchenko, Tim Kopra, Mikhail Kornienko, Sergey Volkov, Scott Kelly and Tim Peake. (NASA TV)
The Soyuz TMA-18M spacecraft undocks carrying Expedition 46 crew members Scott Kelly, Mikhail Kornienko and Sergey Volkov. (NASA TV)