Scientists on NASA’s OSIRIS-REx have found that the Sun’s heat cracks Bennu’s rocks in just 10,000 to 100,000 years, revealing that surface regeneration occurs much faster on asteroids than on Earth.
For the findings, the team analyzed rock fractures on asteroid Bennu from high-resolution images taken by the OSIRIS-REx spacecraft (Origins, Spectral Interpretation, Resource Identification, Regoli Explorer of security).
This information will help scientists estimate how long it takes for rocks from asteroids like Bennu to break down into smaller particles, which can be ejected into space or remain on the asteroid’s surface.
Tens of thousands of years may seem quite slow, but “we thought that the surface regeneration of asteroids took a few million years,” said Marco Delbo, a senior scientist at the Université Côte d’Azur in France.
“We were surprised to learn that the aging and weathering process of asteroids occurs so rapidly, geologically speaking,” said Delbo.
The rapid temperature changes on Bennu have created internal stress that fractures and cracks the rocks, similar to how a cold glass breaks under hot water.
The Sun rises every 4.3 hours in Bennu. At the equator, daytime highs can reach nearly 127 degrees Celsius, and nighttime lows drop to almost minus 23 degrees Celsius.
OSIRIS-REx scientists spotted cracks in the rocks in spacecraft images from early surveys of the asteroid. The fractures appeared to point in the same direction, “a clear signature that temperature shocks between day and night could be the cause,” Delbo said.
Delbo and colleagues hand-measured the length and angles of more than 1,500 fractures in OSIRIS-REx images: some shorter than a tennis racket, others longer than a tennis court.
They found that the fractures are predominantly aligned in a northwest-southeast direction, indicating that they were caused by the Sun, which is shown here as the main force changing Bennu’s landscape.
“If landslides or impacts moved the rocks faster than the cracks, the fractures would point in random directions,” Delbo said.
The scientists used a computer model and their fracture measurements to calculate the time frame of between 10,000 and 100,000 years for thermal fractures to propagate and split the rocks.
“Bennu’s thermal fractures are quite similar to those we find on Earth and Mars in terms of how they form,” said Christophe Matonti, co-author of the paper at the Universitat Côte d’Azur, CNRS, Observatory of the Coast. d’Azur, Geoazur, Sophia-Antipolis, Valbonne, France.
“It’s fascinating to see that they can exist and are similar in very ‘exotic’ physical conditions. [low gravity, no atmosphere]even compared to Mars.”
OSIRIS-REx will return a sample of Bennu to Earth on September 24, 2023.
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