NASA astronaut Scott Kelly to retire after year in space

Less than two weeks after returning to Earth following a year in space, astronaut Scott Kelly announced Friday his retirement from NASA starting on April 1.

"Our universe is a big place, and we have many millions of miles yet to explore," he wrote in a social media post announcing his retirement. "My departure from NASA is my next step on that journey."

On March 2, the 52-year-old returned from a yearlong mission at the International Space Station aimed at studying the effects of long-term galactic travel on humans. He said Friday he will continue to provide samples and submit to other tests as needed for the NASA research project.

Back to Earth last night. Today I head back home! Stretching my space legs on my first refuel stop. #YearInSpace

Posted by NASA Astronaut Scott Kelly on Wednesday, March 2, 2016

Scientists planned to compare his test results with ones from his twin brother, former astronaut Mark Kelly, who remained on Earth during the mission.

While making his roughly 144 million-mile trek around the globe, Kelly shared hundreds of photos on social media of anything from Hurricane Patricia to the Super Bowl, as seen from his vantage point 250 miles above the Earth's surface.

"This year in space mission was a profound challenge for all involved that also gave me a unique perspective and a lot of time to reflect on what my next step should be on our continued journey to help further our capabilities in space and on Earth," he said. "I am very proud of what my NASA colleagues and our partners around the world have accomplished together."

Scott Kelly joined NASA in 1996 while serving in the U.S. Navy. He has been sent to space for four different missions. In his most recent trip, he traveled roughly 144 million miles around the globe.

"My career with the Navy and NASA gave me an incredible chance to showcase public service to which I am dedicated and what we can accomplish on the big challenges of tour day," he said. "I am humbled and excited by new opportunities for me to support and share the amazing work NASA is doing to help us travel farther into the solar system and work with the next generation of science and technology leaders."

Kelly didn't elaborate on what his next move will be.