Scott Kelly and his twin brother also took part in a number of studies
A US astronaut and a Russian cosmonaut have returned to Earth Tuesday after an historic 340-day mission aboard the International Space Station (ISS).
Scott Kelly and Mikhail Kornienko landed in the remote town of Dzhezkazgan in Kazakhstan at 10:26am local time.
"Scott Kelly's one-year mission aboard the International Space Station has helped to advance deep space exploration and America's Journey to Mars," said NASA administrator Charles Bolden.
"Scott has become the first American astronaut to spend a year in space, and in so doing, helped us take one giant leap toward putting boots on Mars".
During the mission, the station crew conducted almost 400 investigations to advance NASA's mission.
Kelly and Kornienko specifically participated in a number of studies - including research into how the human body adjusts to weightlessness, isolation, radiation and the stress of long-duration spaceflight.
Kelly's identical twin brother, former NASA astronaut Mark Kelly, participated in parallel twin studies on Earth to help scientists compare the effects of space on the body and mind down to the cellular level.
One particular research project examined fluid shifts that occur when bodily fluids move into the upper body during weightlessness.
NASA says these shifts may be associated with visual changes and a "possible increase in intracranial pressure, which are significant challenges that must be understood before humans expand exploration beyond Earth's orbit".
The crew also used the opportunity to monitor and capture images of the planet.
They also welcomed the arrival of a new instrument to study the signature of dark matter and conducted technology demonstrations that continue to drive innovation, including a test of network capabilities for operating swarms of spacecraft.
Kelly ventured outside the space station for three spacewalks during his mission.
With the end of this mission, Kelly now has spent 520 days in space, the most among US astronauts - while Kornienko has accumulated 516 days across two flights.
Scott Kelly Back on Earth!
NASA Astronaut Scott Kelly lands safely back on Earth after a historic 340-day mission to the space station. He is all smiles as he is pulled out of the capsule and breathes fresh air for the first time in nearly a year.Details: http://www.nasa.gov/press-release/nasa-astronaut-scott-kelly-returns-safely-to-earth-after-one-year-missionPosted by International Space Station on Tuesday, 1 March 2016