(NASA / Goddard / University of Arizona https://bit.ly/3Q8nAIk)
Planetologists from the University of the Cote d'Azur found numerous cracks on the large boulders of the asteroid Bennu that arose relatively quickly.
The team used data collected by the OSIRIS-REx mission and found the cracks were caused due to the daily heating of the rocks by the Sun and their subsequent cooling.
This must be taken into account when studying the surfaces of other asteroids like Bennu, scientists say.
Low albedo asteroids, such as the parent body of near-Earth asteroid Bennu, are thought to have formed in a protoplanetary disk 4.56 billion years ago.
They formed from primitive matter rich in volatile, prebiotic and organic compounds.
At the same time, Bennu itself was originally formed in the Main Belt as a result of repeated accretion of debris formed after the collision of two large bodies.
During this process, the most ancient substance of the asteroid could have been on the surface of the asteroid.
The matter previously contained inside the parent body of Bennu was subjected to cosmic weathering processes: constant processes of heating and cooling of rocks.
The researchers want to understand the intensity of cosmic weathering because it could help us to correctly interpret observations of an asteroid's regolith.
The work
Now, a group of planetary scientists led by Marco Delbo analyzed the images of the surface of Bennu by the PolyCam camera of the OSIRIS-REx spacecraft.
The instrument examined the asteroid from low orbit and collected a soil sample from it.
The goal of the scientists was large boulders on the surface of Bennu with visible cracks, which could be due to thermal fatigue of the rocks.
In total, Delbo’s team identified 1528 cracks on the Bennu boulders in the latitude range from −50 to +50 degrees, counting from the equator.
They found some cracks were relatively straight, others were irregular, and some had polygonal crack networks.
The shape of the cracks is compatible with the mechanism of formation due to low stresses in the rock generated by daily cycles of temperature changes.
Some well-defined cracks cover the entire length of the boulder, while others affect only a small part of it.
A greater number of cracks are found in the equatorial band compared to the northern and southern average latitudes of the asteroid.
The team concluded that weathering through thermal fatigue of rocks is a fast process that develops on time scales that are much shorter than Bennu's lifetime in near-Earth space .
Cracks as long as those found on Bennu boulders can form over 10,000 to 100,000 years and reduce the thermal conductivity of rocks
This helps to explain the lower thermal inertia of boulders on Bennu and Ryugu compared to meteorites.
At the same time, the influence of such weathering of the asteroid's surface will increase with a decrease in its orbit around the Sun.
Source:
- Nature Geoscience: https://www.nature.com/articles/s41561-022-00940-3
- Space.com: https://www.space.com/asteroid-bennu-cracks-from-sun-osiris-rex-images
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