NASA Mission Helps Solve a Mystery: Why Are Some Asteroid Surfaces Rocky?

Closeup of the rocky surface of the Bennu asteroid. (Credits: NASA/Goddard/University of Arizona)

by Mikayla Mace Kelley
The University of Arizona

Scientists thought Bennu’s surface was like a sandy beach, abundant in fine sand and pebbles, which would have been perfect for collecting samples. Past telescope observations from Earth had suggested the presence of large swaths of fine-grained material smaller than a few centimeters called fine regolith.  But when NASA’s OSIRIS-REx mission arrived at Bennu in late 2018, the mission saw a surface covered in boulders. The mysterious lack of fine regolith became even more surprising when mission scientists observed evidence of processes potentially capable of grinding boulders into fine regolith.

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Highly Porous Rocks Responsible for Bennu’s Surprisingly Craggy Surface

During fall 2019, NASA’s OSIRIS-REx spacecraft captured this image, which shows one of asteroid Bennu’s boulders with a bright vein that appears to be made of carbonate. The image within the circle (lower right) shows a focused view of the vein. (Credits: NASA/Goddard/University of Arizona)

TUCSON, Ariz. (University of Arizona PR) — Scientists thought asteroid Bennu’s surface would be like a sandy beach, abundant in fine sand and pebbles, which would have been perfect for collecting samples. Past telescope observations from Earth’s orbit had suggested the presence of ­­large swaths of fine-grain material called fine regolith that’s smaller than a few centimeters.

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