Smallest object orbited by a spacecraft

At 19:44 UTC on 31 December 2018, spacecraft OSIRIS-REx executed an eight-second thruster firing that inserted the spacecraft in to orbit around an asteroid called 101955 Bennu, which has a mass of 73,270,000,000 kg (73,270,000 tonnes; 80,766,349 US-tons) and a diameter of 510 m (1,673 ft) measured from pole to pole.

The roughly 61-hour orbit sees the spacecraft pass within 1,600 m (5,249 feet) of the asteroid’s centre, which was 112 million kilometres (70 million miles) from Earth at the time of orbital insertion. Thus Bennu becomes the smallest body ever orbited by a spacecraft, and OSIRIS-REx will hope to complete it's mission in retrieving a sample from Bennu by touching the surface in 2020 and returning it to Earth sometime in 2023.

There are nine skyscrapers on Earth taller than the biggest dimension of Bennu