US astronaut Scott Kelly returned to Earth on Wednesday after setting a US record by spending nearly a year in space aboard the International Space Station (ISS).
Kelly and two Russian cosmonauts landed safely in Baikonur Cosmodrome in Kazakhstan, NASA said.
"And touchdown! Welcome home @StationCDRKelly, officially back on Earth after spending a #YearInSpace," NASA said on Twitter.
Kelly returned at 10:26 am Wednesday (0426 GMT) along with two Russian cosmonauts, Mikhail Kornienko and Sergey Volkov of the Russian space agency.
Kelly and Konienko spent 340 days aboard the ISS participating in experiments, doing repairs and going on space walks.
The nearly year-long mission was part of a NASA study to learn about the impact of long duration space flights on the human body.
Kelly presented a special opportunity for study because he is a twin. NASA scientists compared his health data with that of his twin brother, Mark Kelly, a former astronaut, to analyze the changes that occur in space flight on the human body.
According to NASA, it is the first experiment conducted on two people with the same genetics in different space environments.
In Kazakhstan, Scott Kelly will undergo experiments to test the effects that long-term space flight had on his body. The field tests will analyze how his body reacts to different positions and movements.
The mission was the fourth for Kelly. He also holds a record among US astronauts for the most cumulative time in space: 520 days.
Russian cosmonaut Valeri Polyakov holds the record for the longest consecutive number of days in space at 437.