When NASA’s OSIRIS-REx reached the asteroid Bennu in December 2018, the team were met with a rock that was rougher than expected.
“We knew that Bennu would surprise us, so we came prepared for whatever we might find,” said Dante Lauretta, the principal investigator of the OSIRIS-REx mission. “As with any mission of exploration, dealing with the unknown requires flexibility, resources and ingenuity. The OSIRIS-REx team has demonstrated these essential traits for overcoming the unexpected throughout the Bennu encounter.”
The team figured Bennu might throw a curveball at them. That’s why they scheduled nearly a year’s worth of extra time in case something unexpected popped up. A rougher surface falls into this category. If everything went nice and smooth, the team would have narrowed down the potential sample sites to two by now. Instead, the team is going to take a longer look at four sites.
Future high-res imaging of each site will help the OSIRIS-REx team spot areas of fine-grain material perfect for the spacecraft’s sampling instrument.
OSIRIS-REx was designed to collect a sample from an area that looks more like a beach. The team was hoping to find a boulder-free area about 50 meters across. But there isn’t a spot like that on Bennu’s rougher than expected surface. Instead, the team had to find smoother places measuring just 10-20 meters across. Four locations were selected, each named after birds native to Egypt: Nightingale, Kingfisher, Osprey, and Sandpiper.
With the smaller locations selected, the team also developed a new way to get the sample they call “Bullseye TAG.” Images of the asteroid surface will help the spacecraft get to the exact spot at one of these four target locations.
“The extraordinary in-flight performance to date demonstrates that we will be able to meet the challenge that the rugged surface of Bennu presents,” said Rich Burns, project manager for OSIRIS-REx. “That extraordinary performance encompasses not only the spacecraft and instruments, but also the team who continues to meet every challenge that Bennu throws at us.”
The four locations are located all across Bennu’s surface.
Nightingale is the northernmost of the four and is also home to the darkest material of the four.
Kingfisher sits within a small crater near the asteroid’s equator. The exact sample location is free of larger rocks, and it also has the strongest signature for hydrated minerals.
Osprey has several possible sampling locations with its 20 meter across the site. There’s also the strongest signature for carbon-rich material at this spot.
And Sandpiper is a mostly flat area situated in Bennu’s southern hemisphere. The team believes this location also has hydrated minerals present.
In a few months, OSIRIS-REx will begin close passes over each site from a distance of less than a mile. The team will confirm each place is safe to land and contains material that can be sampled by the spacecraft. High-res imaging of these locations will map out features and potential obstacles to help the spacecraft’s autonomous navigation to Bennu’s surface.
With this upcoming data, two final locations will be selected in December. This will be followed by a second and third reconnaissance flyby early next year to gather even better images of the surface at these locations. All this data will hopefully lead to a successful sample mission in the second half of 2020.
If the rest of the mission goes as smoothly as it already has, a piece of Bennu will be back on Earth on September 24, 2023.