Foreign: One of Earth’s closest planetary neighbors is an asteroid roughly the height of a skyscraper. It is a remnant from the dawn of the solar system, made of carbon-rich rocks and boulders. Since late 2018, this asteroid, called Bennu, has been the home of NASA’s Osiris-Rex Mission.
When Osiris-Rex arrived at Bennu, it began wrapping the asteroid in a complex web of observations. It started with a preliminary survey of Bennu’s size, shape, mass, and spin. On New Year’s Eve, Osiris-Rex was captured into orbit by Bennu’s minuscule gravity, making it the smallest world ever to be orbited by a spacecraft.
In early 2019, Osiris-Rex broke orbit to conduct a detailed survey of Bennu. It globally mapped the asteroid at a resolution of only five centimeters per pixel, the highest resolution of any planetary body, including Earth. It studied geological features at different latitudes and times of day, enabling stereo imaging and landmark-based navigation.
Osiris-Rex concluded its first year at Bennu back in orbit, circling the asteroid’s terminator, the boundary between day and night. Here, outside forces acting on the spacecraft are balanced, allowing it to orbit within the same plane over time.
Reconnaissance resumed in early 2020 with close flyovers of the primary sample collection site, Nightingale, and the backup site, Osprey. Osiris-Rex performed two rehearsals prior to the sample collection event, descending close to the asteroid’s surface and then backing away.
On August 11th, 2020, Osiris-Rex departed its home orbit and made a four-hour traverse to Bennu’s Northern Hemisphere, retracing its earlier path. It performed engine burns to match Bennu’s rotation before descending to an altitude of approximately 40 meters.
The most crucial moment of the mission arrived on October 20th, 2020. The spacecraft departed orbit and performed the touch-and-go sample collection maneuver at the Nightingale site. Osiris-Rex touched down and collected its sample, exceeding the goal of collecting 60 grams of asteroid material.
After collecting the sample, Osiris-Rex drifted to a safe distance away from Bennu. Mission controllers directed it to stow the sample in preparation for return to Earth. Before departing Bennu, Osiris-Rex flew over the Nightingale site to observe how the sample collection event had changed the surface.
With that, Osiris-Rex had recorded its mark on Bennu and completed its mission.
