The asteroid Bennu as imaged by the OSIRIS-REx spacecraft at a distance of 80 kilometres (50 miles). Image: NASA/Goddard/University of Arizona
On New Year’s Eve, while many scientists, engineers and space enthusiasts focused on NASA’s New Horizons probe as it raced toward Ultima Thule in the remote Kuiper Belt, another team of flight controllers was carrying out its own record-breaking manoeuvre closer to home: guiding the OSIRIS-REx spacecraft into orbit around a tiny asteroid named Bennu.
At 7:43 UTC on 31 December, 112 million kilometres (70 million miles) from Earth, OSIRIS-REx executed an eight-second thruster firing that allowed the spacecraft to be captured by Bennu’s minuscule gravity, just five millionths as strong as Earth’s. The resulting 62-hour orbit carries the spacecraft within 1.75 kilometres (about 1 mile) of the asteroid’s centre.
Bennu is the smallest body ever orbited by a spacecraft. It resembles a somewhat tetrahedron-shaped rubble pile measuring about 510 metres (1,673 feet) across from pole to pole. For comparison, there are currently nine skyscrapers around the world that are taller than the asteroid’s polar width.
The $1 billion OSIRIS-REx mission was launched in September 2016 and reached reached Bennu’s immediate vicinity on 3 December. After exhaustive observations from ...