NASA spacecraft observes asteroid Bennu’s ‘bulletproof vest’

This image shows the rock-covered surface of asteroid Bennu. It was taken by the PolyCam camera on NASA’s OSIRIS-REx spacecraft on April 11, 2019 from a distance of 2.8 miles (4.5 km). The field of view is 211 feet (64.4 m) and the large rock in the upper right corner of the image is 50 feet (15.4 m) high. When the image was taken, the spacecraft was over the southern hemisphere, pointing PolyCam far north and west. Credit: NASA/Goddard/University of Arizona

Asteroid Bennu’s boulder-covered surface gives it protection from small meteor impacts, according to crater observations by NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) spacecraft .

“These observations provide new insight into how asteroids like Bennu respond to energetic impacts,” said Edward (Beau) Bierhaus of Lockheed Martin Space, Littleton, Colorado, lead author of a paper published in this month’s issue. from nature geoscience.

Bennu is a “rubble pile” asteroid, meaning it formed from the debris of a much larger asteroid that was destroyed by an ancient impact. The fragments from the collision coalesced under their low gravity to form Bennu.

The team used unprecedented high-resolution global datasets to examine Bennu’s craters: images from the OSIRIS-REx camera suite and surface height (topography) data derived from the OSIRIS- REx, a laser ranging instrument (lidar). on the spaceship.

“Measuring craters and their population on Bennu was exceptionally exciting,” said David Trang of the University of Hawaii at Mānoa, Honolulu, co-author of the paper. “At Bennu, we discovered something unique with small, rocky bodies, which broadened our knowledge of the impacts.”

Planetary scientists can estimate the age of surfaces by measuring the abundance and size of craters. Impact craters accumulate over time, so a surface with many craters is older than a surface with few craters. Also, the size of the crater depends on the size of the impactor, with larger impactors generally creating larger craters. Because small meteoroids are much more abundant than large meteoroids, celestial objects like asteroids typically have many more small craters than large ones.

Bennu’s largest craters follow this pattern, with the number of craters decreasing as their size increases. However, for craters less than about 6.6 to 9.8 feet (about 2 to 3 meters) in diameter, the trend is reversed, with the number of craters decreasing as their size decreases. This indicates that something unusual is happening on the surface of Bennu.

The researchers believe that Bennu’s profusion of boulders acts as a shield, preventing many small meteoroids from forming craters. Instead, these impacts are more likely to shatter rocks or chip and fracture them. Additionally, some rock-cutting impactors create smaller craters than they would if Bennu’s surface were covered with smaller, more uniform particles, such as beach sand.

This activity causes Bennu’s surface to change differently from fine-grained or solid-surface objects. “The displacement or disruption of an individual or small group of rocks by a small impact is probably one of the fastest processes on the surface of a rubblepile asteroid. On Bennu, this contributes to make the surface much younger than the interior,” Bierhaus said.


Study of craters on asteroid Bennu shows how long it has been orbiting near Earth


More information:
EB Bierhaus et al, Crater population on asteroid (101955) Bennu indicates impact shielding and a young surface, nature geoscience (2022). DOI: 10.1038/s41561-022-00914-5

Provided by NASA’s Goddard Space Flight Center

Quote: NASA spacecraft observes ‘bulletproof vest’ from asteroid Bennu (Jun 16, 2022) Retrieved June 17, 2022 from https://phys.org/news/2022-06-nasa-spacecraft-asteroid -bennu-boulder.html

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