Choosing the Candidate Sample Collection Sites
Each of the four candidate sample sites on Bennu were chosen based on their scores for safety, sampleability, deliverability, and science value. Sites with safe surrounding topography were selected because the spacecraft must be protected as it descends to, touches and collects a sample from the asteroid’s surface. The four sites were also evaluated for the amount of sampleable material they contain. Sites with high sampleability contain material that can be ingested by the spacecraft’s sample mechanism head. To be considered ingestible, rocks and debris must be 2.5 cm or smaller. Deliverability evaluates the relative ease for the spacecraft to be maneuvered in and out of a site. The four sites also have high science value. Science value evaluates the surface properties of each site by measuring the presence of carbon-rich materials, presence of hydrated minerals, alteration of regolith, diversity in material composition and evidence of primitive materials. In December 2019, the OSIRIS-REx team chose sites Nightingale and Osprey as the mission’s primary and backup sample collection sites.
Site Nightingale is the primary sample collection site on Bennu. It is located in a crater (with a 33 ft, or 10 m, radius) near Bennu’s north pole.
Site Osprey is the backup sample collection site on Bennu. Located near the asteroid’s equator, Osprey is set in a small crater with a 33 ft (10 m) radius.
Site Kingfisher is located near Bennu’s equator in a small crater that has a radius of 13 ft (4 m). Kingfisher is surrounded by boulders, but the site itself, with a radius of 16 ft (5 m), is free of large rocks.
Site Sandpiper is in asteroid Bennu’s southern hemisphere, on the southeast floor of a large crater with a radius of 103 ft (31.5 m). The site itself is a relatively flat area with a 16 ft (5 m) radius.