NASA's OSIRIS-REx team has selected four potential sites for the agency's first asteroid sample return mission. The spacecraft started mapping asteroid Bennu's surface as soon as it arrived in late 2018, and scientists part of its ground team thought they'd be choosing the final two candidate sites at this point in time. Observations made from our planet showed that the asteroid had large areas with fine-grain materials, but images the spacecraft took showed the truth: Bennu has an especially rocky terrain, making it a challenge to collect materials less than 1 inch in diameter. That's the maximum size the probe's sample mechanism can handle.
The fact that OSIRIS-Rex was designed to identify sample sites with an 82-foot radius made things even more difficult. To be able to find four boulder-free areas, the mission team had to adjust the spacecraft's sample site identification process to be able to detect sites with a radius of 16 to 33 feet. The scientists also had to give its navigation capabilities an accuracy boost to be able to target smaller sites than expected.
The OSIRIS-Rex team stuck to the mission's Egyptian-themed naming scheme and christened the four sites Nightingale, Kingfisher, Osprey and Sandpiper -- all birds native to Egypt. They vary in geological features: Nightingale contains fine-grain dark materials, Kingfisher has hydrated minerals, Osprey may have carbon-rich materials, while Sandpiper could yield water-rich samples. OSIRIS-REx will take close-up images of the four sites and analyze them in detail this fall. That will provide the mission team the data it needs to choose the primary and backup sample sites in December.