High-resolutions images of asteroid Bennu from NASA's OSIRIS-REx spacecraft offer scientists the opportunity to analyze the processes that break down boulders on the surfaces of airless bodies, Planetary Science Institute Research Scientist Jamie Molaro said.

Breakdown can occur due to impacts on the surface, movement of boulders in landslides, and thermal fracturing. Thermal fracturing is a process where cracks can form in boulders due to heating and cooling from the Sun over time. This process is believed to be very important on certain objects in the solar system. However, it is hard to observe because it happens at small scales.

"Based on what we're seeing in these images, we believe rock breakdown due to thermal fracturing is happening on Bennu. What is really exciting is that this is the first time we're observing direct evidence for this process on a planetary surface," Molaro said during a presentation at the 50th Lunar and Planetary Science Conference held this week in The Woodlands, Texas [https://www.hou.usra.edu/meetings/lpsc2019].

Until OSIRIS-REx arrived at Bennu, scientists relied primarily on numerical models and laboratory studies to understand the nature of this process. We have learned that boulder size and composition play a big role in how thermal fracturing operates because it changes the boulder's response to heating and cooling.

For example, it may erode small dust grains from the surface of one rock but develop larger fractures in another that can split a boulder into many pieces.

Now, the results from these computer models and laboratory studies can be compared directly to observations from the spacecraft, allowing us to better understand how it works to break down rocks and produce dust on asteroid surfaces.

"The OSIRIS-REx mission to Bennu offers an unprecedented opportunity to search for evidence of thermal breakdown occurring in-situ on its surface. Characterizing this process is key to understanding Bennu's surface evolution and properties," Molaro said. "This analysis may also assist with sample site selection and eventually sample analysis."

Molaro's research was funded by a grant to PSI from NASA's OSIRIS-Rex Participating Scientists program.

Related Links
OSIRIS-REx at NASA
Asteroid and Comet Mission News, Science and Technology

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OSIRIS-REx images close in on Bennu's northern hemisphere
Greenbelt MD (SPX) Mar 15, 2019
This trio of images acquired by NASA's OSIRIS-REx spacecraft shows a wide shot and two close-ups of a region in asteroid Bennu's northern hemisphere. The wide-angle image (left), obtained by the spacecraft's MapCam camera, shows a 590-foot (180-meter) wide area with many rocks, including some large boulders, and a "pond" of regolith that is mostly devoid of large rocks. The two closer images, obtained by the high-resolution PolyCam camera, show details of areas in the MapCam image, specifica ... read more