At just 1,600 feet (500 meters) across, Bennu is the smallest celestial body ever to be orbited by a spacecraft. Picture: Conceptual Image Lab/Goddard Space Flight Center/NASA via AP

Washington - US space scientists selected a site on the distant asteroid Bennu for the OSIRIS-Rex spacecraft to swoop down, grab a sample from the orb’s boulder-strewn surface and return to earth, NASA said in a press release on Thursday.

"The area safe enough for the spacecraft to touch is much smaller – approximately 52 feet (16 meters) in diameter, resulting in a site that is only about one-tenth the size of what was originally envisioned," the release said.

NASA explained the site was selected after the spacecraft spent a year stalking and scoping the asteroid​​​.

Additional reconnaissance flights will be needed for the "touch-and-go" sample collection attempt, the release said.

The spacecraft will begin its journey back to earth in 2021 and is scheduled to return to Earth in September 2023, the release added.

This artist's rendering made available by NASA in July 2016 shows the mapping of the near-Earth asteroid Bennu by the OSIRIS-REx spacecraft. Picture: NASA/Goddard/University of Arizona via AP

By studying the sample from the space rock, scientists hope to learn details of how the Solar System formed, according to the release.

This mosaic image composed of 12 PolyCam images collected on December 2, 2018, and provided by NASA shows the asteroid Bennu. File picture: NASA/Goddard/University of Arizona via AP