Launched in September 2016, NASA’s first probe to a near-Earth asteroid has traveled approximately 1.1 billion miles. It will arrive at Bennu in December of this year and fly by the asteroid’s poles and equator before entering orbit.
From a distance of 1.4 millon miles, the spacecraft’s PolyCam camera photographed its target on August 17.
“Right now, Bennu just looks like a star, a point source. That will change in November, when we begin detailed observations, and we’ll start seeing craters and boulders. You could say that’s when our asteroid will transition from being an astronomical object to an actual geological object,” said OSIRIS-REx working group lead and University of Arizona Lunar and Planetary Laboratory (LPL) staff scientist Carl Hergenrother.
Between now and the probe’s arrival date, its science instruments, which include a thermal spectrometer, a visible and infrared spectrometer, a laser altimeter, and an X-ray spectrometer, will gather data about Bennu.
Early flybys will occur at distances ranging from 4.4 to 11.8 miles above the asteroid’s surface, a challenging maneuver because Bennu is so small and has very weak gravity.
Based on the spacecraft’s studies of Bennu, the mission team will select two possible sample collection sites. Collection will occur in July 2020, followed by a return to Earth. The samples will be placed in a Sample Return Capsule, which the probe will eject to land in the Utah desert in September 2023.
“The story of this asteroid is the story of our solar system. When we understand Bennu, we will understand something fundamental about our solar system,” stated OSIRIS-REx Camera Suite (OCAMS) instrument scientist Bashar Rizk.
PolyCam, one of three cameras on the spacecraft, is designed to function as both a long-range acquisition camera that will photograph Bennu on approach, and as a reconnaissance camera, which will take detailed images of Bennu once OSIRIS-REx arrives at its target.
After conducting a slingshot or gravity assist maneuver around the Earth last December to raise it to Bennu’s orbital plane, OSIRIS-REx has been traveling close to 32,000 miles per hour on its way to Bennu.
“Now that OSIRIS-REx is close enough to observe Bennu, the mission team will spend the next few months learning as much as possible about Bennu’s size, shape, surface features, and surroundings before the spacecraft arrives at the asteroid,” explained OSIRIS-REx principal investigator Dante Lauretta of the University of Arizona.
“After spending so long planning for this moment, I can’t wait to see what Bennu reveals to us.”