Surface of the asteroid Bennu was significantly more porous than its average material.

(ORDO NEWS) — When the OSIRIS-REx spacecraft collected soil samples from the surface of the asteroid Bennu in 2020, scientists measured the forces generated by such interaction and were able to directly test the physical properties of the poorly understood upper subsurface layer of asteroids such as “rubble pile”.

Now, in a new study, astronomers have characterized the top layer of the asteroid’s surface as consisting of loosely bonded rock fragments with void volumes between them roughly twice the average void volume calculated for the asteroid’s material as a whole.

“The low gravity of rubble asteroids such as Bennu weakens the bonding forces between the elements of its upper subsurface, as they experience only a small compressive effect, and particle cohesion is minimal,” said study lead author Dr. Kevin Walsh. ) from the Southwestern Research Institute, USA.

“We conclude that the loose, loosely bound topsoil is more likely to have a global distribution over the surface of the asteroid Bennu, rather than localized only in the sampling area.”

Asteroid Bennu, which fits well the definition of a “rubble pile” asteroid, is a spherical formation of rock fragments about 500 meters in diameter, held together by gravity. This asteroid is believed to have been formed by a collision involving a larger Asteroid Belt object.

A large number of rocks are scattered across the asteroid’s cratered surface, indicating a “turbulent past” for the asteroid after its separation from its larger parent body millions or billions of years ago.

The goal of the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission is to collect and deliver to Earth in 2023 at least 60 grams of material from the surface of the asteroid Bennu. Sampling operations have provided additional information about this asteroid.

Soil sampling operations were captured using the Sample Acquisition Verification Camera (SamCam) of the OSIRIS-REx probe’s Camera Suite, which tracked the movements of a robotic arm called the Touch-and-Go Sample Acquisition Mechanism (TAGSAM).

Analysis of these images showed that contact with the surface led to significant movements of rock fragments – almost every particle observed in the camera’s field of view was moved or rotated within the area with a radius of about 40 centimeters, in which operations were performed using the TAGSAM tool.

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