NASA’s team leading the first asteroid sample return mission OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) has officially selected a sample collection site on the asteroid Bennu’s boulder-scattered surface.
The mission team spent the past several months evaluating close-range data from four candidate sites in order to identify the best option for the sample collection. It concluded that a site located in a crater high in Bennu’s northern hemisphere — designated “Nightingale” — is the best spot for the OSIRIS-REx spacecraft to snag its sample.
“After thoroughly evaluating all four candidate sites, we made our final decision based on which site has the greatest amount of fine-grained material and how easily the spacecraft can access that material while keeping the spacecraft safe,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona in Tucson. “Of the four candidates, site Nightingale best meets these criteria and, ultimately, best ensures mission success.”
The other candidate sites apart from Nightingale were Sandpiper, Osprey, and Kingfisher all of which were chosen for investigation because these potential sampling regions on asteroid Bennu pose the fewest hazards to the spacecraft’s safety while still providing the opportunity for great samples to be gathered.
The site Nightingale is located in a northern crater that is 140 meters wide. “Nightingale’s regolith or rocky surface material is dark, and images show that the crater is relatively smooth. Because it is located so far north, temperatures in the region are lower than elsewhere on the asteroid and the surface material is well-preserved.” NASA said.
“The crater also is thought to be relatively young, and the regolith is freshly exposed. This means the site would likely allow for a pristine sample of the asteroid, giving the team insight into Bennu’s history,” NASA added.
Although Nightingale ranks the highest of any location on Bennu, the site still poses challenges for sample collection. As per NASA, any significant disturbance to Nightingale’s surface would make it difficult to collect a sample from that area. That is why the mission also selected Osprey as a backup sample collection site.
The spacecraft is designed to autonomously “wave-off” from the site if its predicted position is too close to a hazardous area. “During this manoeuvre, the exhaust plumes from the spacecraft’s thrusters could potentially disturb the surface of the site, due to the asteroid’s microgravity environment,” NASA said. In any situation where a follow-on attempt at Nightingale is not possible, the team will try to collect a sample from site Osprey instead.