SAN FRANCISCO — After a year of meticulously mapping the asteroid Bennu’s surprisingly boulder-littered surface (SN: 3/19/19), NASA has finally picked a sample collection site.
OSIRIS-REx, on NASA’s first mission to bring a bit of asteroid back to Earth, will touch down at a site called Nightingale, inside a dark, relatively smooth crater in Bennu’s northern hemisphere. “What really drove the decision for me, here, on this site was the scientific value,” OSIRIS-REx principal investigator Dante Lauretta said December 12 in a news conference at the American Geophysical Union annual meeting.
Because Nightingale lies so far north, its surface material is chillier than other parts of the asteroid. “Cool is good because we’re interested in organic material, and we’re interested in hydrated minerals,” which are generally better preserved in cooler conditions, said Lauretta, of the University of Arizona in Tucson. Investigating that material may offer insight into early solar system conditions and hint whether an asteroid like Bennu could have delivered the chemical precursors for life to Earth (SN: 1/15/19).
But the Nightingale site is high-risk, high-reward. “It’s kind of a tight fit” to park a 6-meter-wide spacecraft in a 20-meter-wide crater, Lauretta said. And “there are some substantial hazards even within the crater itself,” such as a wall of rocks on the eastern edge. That wall includes a pointy rock, which Lauretta has nicknamed “Mount Doom,” looming 10 meters above the sample collection site.
Lauretta is confident that OSIRIS-REx will safely snag a sample from Nightingale. But as a backup, the team has also picked a similarly sized crater near Bennu’s equator, Osprey. Osprey contains less fine-grained material than Nightingale — a potential challenge to OSIRIS-REx’s sample collector, which is designed to swallow particles smaller than a couple of centimeters. But Osprey is relatively free of hazards that OSIRIS-REx might fly into, Lauretta said.
OSIRIS-REx will now make more detailed observations of Nightingale and Osprey at low altitudes and perform two sample collection rehearsals — ducking to 50, then 25, meters above the asteroid’s surface — before its first attempt to collect a sample in August 2020.