NASA weighs up four hazardous sampling sites on asteroid Bennu
Having nearly completed its long journey to the asteroid Bennu and collected a couple of orbital records along the way, NASA’s OSIRIS-REx spacecraft is now being readied for its most critical maneuver, sample collection. After combing through the probe’s recent observations of the rocky body, mission scientists are now in the process of selecting which of the four possible sites it will target for a sampling attempt, which is expected to take place midway through next year.
The OSIRIS-REx mission is NASA’s first asteroid sampling mission, and all going to plan, will follow a similar path to Japan’s Hayabusa2 probe, which recently departed asteroid Ryugu with its samples securely onboard.
Since July, NASA has been weighing up four candidate sites for its sampling attempt, which were given the bird-inspired names of Sandpiper, Osprey, Kingfisher and Nightingale. Since then, OSIRIS-REx has been circling the asteroid and gathering images of each site so scientists can closely examine which is most suitable for their means.
This involves looking at how fine the surface material is and therefore how easily it can be collected, along with the topography of the area, the color and the albedo, or reflectivity. These images have revealed a more rugged terrain than NASA had planned and hoped for, void of large clear areas with piles of sandy material that would have been attractive targets and instead strewn with hazardous boulders that could bring the whole thing undone.
“Sample site selection really is a comprehensive activity. It requires that we look at many different types of data in many different ways to ensure the selected site is the best choice in terms of spacecraft safety, presence of sampleable material, and science value,” says Heather Enos, OSIRIS-REx deputy principal investigator. “Our team is incredibly innovative and integrated, which is what makes the selection process work.”
Each of the four candidates have their strengths and weaknesses as sampling sites. Sandpiper is mostly flat, but its sandy material is wedged between bigger rocks. Osprey seems to have a nice variety of carbon-rich material, but the particles may be too large for the sampling mechanism to collect.
Kingfisher was selected because it is inside a young crater with what is likely fresher material. The probe’s flyovers revealed that this crater may be too rocky, but scientists have spotted a nearby crater that could also serve their purpose. Nightingale appears to be packed with fine, unobstructed material, but is farther north where the lighting conditions could confuse the craft’s navigation systems.
“Bennu’s challenges are an inherent part of this mission, and the OSIRIS-REx team has responded by developing robust measures to overcome them,” says Mike Moreau, OSIRIS-REx deputy project manager at Goddard. “If the spacecraft executes a wave-off while attempting to collect a sample, that simply means that both the team and the spacecraft have done their jobs to ensure the spacecraft can fly another day. The success of the mission is our first priority.”
In the coming days, NASA expects to make a decision on not just a primary site, but a backup option as well. Its preparations for the sampling attempt will include more reconnaissance flyovers in the early parts of next year, along with spacecraft touchdown rehearsals. Sample collection is scheduled for summer 2020, while OSIRIS-REx is expected back on home soil in September 2023.
The video below provides an update on the mission and its discoveries so far.