US spacecraft enters orbit around asteroid

NASA's Osiris-Rex spacecraft has entered orbit around an asteroid that's 110 million km from Earth, on a quest to bring back samples to Earth.

The 500-metre-wide Bennu asteroid now has a NASA space probe orbiting it. (AAP)

A NASA spacecraft has gone into orbit around an ancient asteroid, setting a pair of records.

The Osiris-Rex spacecraft entered orbit on Tuesday (AEDT) around the asteroid Bennu, 110 million kilometres from Earth.

It's the smallest celestial body ever to be orbited by a spacecraft. Bennu is just 500 metres across.

The spacecraft's laps are just 1.75 km above the asteroid's surface, another record.

Osiris-Rex arrived at Bennu in early December and flew in formation with it until the latest manoeuvre.

The goal is to grab gravel samples in 2020 for return to Earth in 2023.

The New Year's Eve milestone occurred just hours before another NASA explorer, New Horizons, was set to fly past an icy space rock beyond Pluto.