Closest orbit of an asteroid

The smallest orbit by a spacecraft around a planetary body was achieved by NASA's OSIRIS-REx spacecraft around the asteroid 101955 Bennu. On 6 October 2020, the spacecraft maneouvred into a transfer orbit with a semi-major axis (average altitude) of just 832 metres. At its closest point, it was just 374 metres above the surface of Bennu.

The record-breaking transfer orbit was achieved as part of the preparations for the TAG (touch-and-go) manoeuvre that would see the spacecraft take samples from the asteroid's surface. It remained in this orbit for 2 days.

Bennu's very low mass (around 73 million tonnes vs 5,972 quintillion tonnes for Earth), means that it has an extremely weak gravitational pull. The International Space Station, for example, has to maintain an orbital speed of around 27,000 km/h (17,000 mph) to keep from being pulled down to Earth. OSIRIS-REx, by contrast, is travelling around Bennu at between 4.6 and 5.8 cm/s (0.2 km/h; 0.13 mph) but still has to use solar pressure and careful adjustments to prevent it from drifting away. It takes just over 61 hours for the spacecraft to complete a single orbit.