Asteroid Bennu: NASA selects final 4 site candidates for second most DANGEROUS space rock sample return

Asteroid 101955 Bennu is a carbonaceous asteroid in the Apollo group discovered by the LINEAR Project on 11 September 1999. It has a mean diameter of approximately 492 metre (the size of the Empire State building) and it may collide with our planet in 2135. The gigantic asteroid has an estimated weight of 79 billion kilograms. Recently, NASA grabbed the closest shot of the asteroid Bennu. And now, NASA’s asteroid-sampling OSIRIS-REx spacecraft will soon attempt to obtain and return a sample from the near-Earth asteroid. Yes, you read it right. NASA has announced that it has selected final four site candidates for the ambitious asteroid sample return attempt.

Asteroids, asteroids and only asteroids. Now-a-days you must be hearing a lot about asteroids. Aren’t you? Well, asteroids are small, rocky objects that orbit the Sun. The space rocks approach towards the Earth due to the gravitational forces that affect them. There are more than 7 lakh asteroids that have been found in space. Asteroids can bring tsunamis, shock waves and flattening winds that could be catastrophic. Recently, many deadly asteroids including 2019 OK, 2019 OD, 2015 HM10, 2019 OE, 2019 NN3, 2019 MB4, 2019 MT2, 2006 QV89, 2016 NO56M, RF12 and others approached towards the Earth, fortunately did not hit out planet.

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Coming back to asteroid Bennu, the gigantic space rock has an estimated 1-in-2,700 chance of impacting our planet between 2175 and 2199. It is the second-most dangerous known space rock.

According to the NASA, The four candidate sample sites on Bennu are designated Nightingale, Kingfisher, Osprey, and Sandpiper – all birds native to Egypt. The naming theme complements the mission’s two other naming conventions – Egyptian deities (the asteroid and spacecraft) and mythological birds (surface features on Bennu).

Pictured are the four candidate sample collection sites on asteroid Bennu selected by NASA’s OSIRIS-REx mission (Photo Credit: NASA/University of Arizona)

Pictured are the four candidate sample collection sites on asteroid Bennu selected by NASA’s OSIRIS-REx mission (Photo Credit: NASA/University of Arizona)

The four sites are diverse in both geographic location and geological features. While the amount of sampleable material in each site has yet to be determined, all four sites have been evaluated thoroughly to ensure the spacecraft’s safety as it descends to, touches and collects a sample from the asteroid’s surface.

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Nightingale is the northern-most site, situated at 56 degrees north latitude on Bennu. There are multiple possible sampling regions in this site, which is set in a small crater encompassed by a larger crater 459 feet (140 m) in diameter. The site contains mostly fine-grain, dark material and has the lowest albedo, or reflection, and surface temperature of the four sites.

Kingfisher is located in a small crater near Bennu’s equator at 11 degrees north latitude. The crater has a diameter of 26 feet (8 m) and is surrounded by boulders, although the site itself is free of large rocks. Among the four sites, Kingfisher has the strongest spectral signature for hydrated minerals.

Video Credit: NASA

Osprey is set in a small crater, 66 feet (20 m) in diameter, which is also located in Bennu’s equatorial region at 11 degrees north latitude. There are several possible sampling regions within the site. The diversity of rock types in the surrounding area suggests that the regolith within Osprey may also be diverse. Osprey has the strongest spectral signature of carbon-rich material among the four sites.

Sandpiper is located in Bennu’s southern hemisphere, at 47 degrees south latitude. The site is in a relatively flat area on the wall of a large crater 207 ft (63 m) in diameter. Hydrated minerals are also present, which indicates that Sandpiper may contain unmodified water-rich material.

In a press release, the US space agency said, “After months grappling with the rugged reality of asteroid Bennu’s surface, the team leading NASA’s first asteroid sample return mission has selected four potential sites for the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft to “tag” its cosmic dance partner.”

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NASA further said, “Since its arrival in December 2018, the OSIRIS-REx spacecraft has mapped the entire asteroid in order to identify the safest and most accessible spots for the spacecraft to collect a sample. These four sites now will be studied in further detail in order to select the final two sites – a primary and backup – in December.”

“The team originally had planned to choose the final two sites by this point in the mission. Initial analysis of Earth-based observations suggested the asteroid’s surface likely contains large “ponds” of fine-grain material. The spacecraft’s earliest images, however, revealed Bennu has an especially rocky terrain. Since then, the asteroid’s boulder-filled topography has created a challenge for the team to identify safe areas containing sampleable material, which must be fine enough – less than 1 inch (2.5 cm) diameter – for the spacecraft’s sampling mechanism to ingest it,” it added.

“We knew that Bennu would surprise us, so we came prepared for whatever we might find,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. “As with any mission of exploration, dealing with the unknown requires flexibility, resources and ingenuity. The OSIRIS-REx team has demonstrated these essential traits for overcoming the unexpected throughout the Bennu encounter.”

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