A NASA spacecraft has arrived at the ancient asteroid Bennu after a two-year journey, its first visitor in billions of years.
The robotic explorer Osiris-Rex pulled within 12 miles of the diamond-shaped space rock on Monday.
It will get even closer in the days ahead and go into orbit around Bennu on December 31.
No spacecraft has ever orbited such a small cosmic body.
Flight controllers in Littleton, Colorado, applauded and exchanged high-fives once confirmation came through. It comes exactly one week after NASA landed a spacecraft on Mars.
"Relieved, proud, and anxious to start exploring!" tweeted lead scientist Dante Lauretta of the University of Arizona.
Bennu is estimated to be just over 1,600 feet (500 metres) across. The spacecraft, which is about the size of an SUV, will shadow it for a year before scooping up some gravel for return to Earth in 2023.
It is expected to use a 10-foot mechanical arm in 2020 to momentarily touch down and vacuum up particles. The sample container should then break loose and head back to Earth in 2021.
The collection would represent the biggest cosmic haul since the Apollo astronauts hand-delivered moon rocks to Earth in the late 1960s and early 1970s.
Scientists are eager to study material from a carbon-rich asteroid like Bennu, which could hold evidence dating back to the beginning of our solar system 4.5 billion years ago.
A Japanese spacecraft, meanwhile, has been hanging out at another asteroid since June, also to collect samples.
The unmanned Hayabusa2 spent three-and-a-half years travelling 170 million miles from earth to an asteroid named Ryugu.
Both missions could provide vital clues to the origin of the solar system and life on Earth.
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