NASA has marked the spot it wants to steal a batch of dirt from an asteroid.
The spot, known as Nightingale, is a 20-metre wide crater which forms part of asteroid Bennu, which is millions of kilometres from planet Earth.
NASA said it had spent a year working out the best spot of the asteroid to take from the OSIRIS-REx spacecraft.
OSIRIS-REx spacecraft was launched on 8 September 2016, from Cape Canaveral Air Force Station. The spacecraft reached Bennu in 2018 and is due to return the sample to Earth in 2023.
Engineers picked the Nightingale site from four final candidate spots on Bennu, arguing it could be the best place to find organic material and water on the asteroid that may hail from the earliest days of the Solar System.
“This one really came out on top, because of the scientific value,” Dante Lauretta, the principal investigator of the asteroid sampling mission at the University of Arizona in Tucson, said at a press conference announcing the selection.
“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.
Nightingale is located in a northern crater 460 feet (140 meters) wide on the asteroid. 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. 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.
Although Nightingale ranks the highest of any location on Bennu, the site still poses challenges for sample collection. The original mission plan envisioned a sample site with a diameter of 164 feet (50 meters). While the crater that hosts Nightingale is larger than that, the area safe enough for the spacecraft to touch is much smaller – approximately 52 feet (16 meters) in diameter, resulting in a site that is only about one-tenth the size of what was originally envisioned. This means the spacecraft has to very accurately target Bennu’s surface. Nightingale also has a building-size boulder situated on the crater’s eastern rim, which could pose a hazard to the spacecraft while backing away after contacting the site.
The mission also selected site Osprey as a backup sample collection site. The spacecraft has the capability to perform multiple sampling attempts, but any significant disturbance to Nightingale’s surface would make it difficult to collect a sample from that area on a later attempt, making a backup site necessary. 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. In any situation where a follow-on attempt at Nightingale is not possible, the team will try to collect a sample from Osprey.
“Bennu has challenged OSIRIS-REx with extraordinarily rugged terrain,” said Rich Burns, OSIRIS-REx project manager at NASA’s Goddard Space Flight Center. “The team has adapted by employing a more accurate, though more complex, optical navigation technique to be able to get into these small areas. We’ll also arm OSIRIS-REx with the capability to recognise if it is on course to touch a hazard within or adjacent to the site and wave-off before that happens.”
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