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This asteroid Bennu mosaic was created using observations by NASA’s OSIRIS-REx spacecraft, which has been in close proximity to the asteroid for more than two years. Credit: NASA/Goddard/University of Arizona
Recently, scientists from NASA’s OSIRIS-REx mission discovered that surface regeneration occurs on asteroids much more quickly than it does on Earth. By analyzing high-resolution images of rock fractures on the asteroid Bennu, taken by[{” attribute=””>OSIRIS-REx spacecraft, the researchers discovered that the Sun’s heat fractures rocks on Bennu in only 10,000 to 100,000 years. With the use of this knowledge, scientists will be able to better predict the time it takes boulders on asteroids like Bennu to fragment into smaller pieces, some of which may eject into space while others may remain on the asteroid’s surface.
Although tens of thousands of years might sound pretty slow, “we thought surface regeneration on asteroids took a few millions of years,” said Marco Delbo, senior scientist at Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, Laboratoire Lagrange, Nice, France, and lead author of a paper published in June 2022 in the journal 
The PolyCam aboard NASA’s OSIRIS-REx spacecraft provided high-resolution, microscope-like images of asteroid Bennu’s surface. This made it possible for researchers to map more than 1,500 rock fractures. Credit: NASA/Goddard/University of Arizona
Rapid temperature changes on asteroid Bennu create internal stress that fractures and breaks down rocks, comparable to how a cold glass breaks under hot water. On Bennu, the Sun rises every 4.3 hours. At the equator, daytime highs can reach almost 260°F (about 127°C), and nighttime lows plummet to nearly minus 10°F (about minus 23°C).
OSIRIS-REx scientists spotted cracks in the rocks in spacecraft images from the first surveys of the asteroid. All of the fractures seemed to point in the same direction, “a distinct signature that temperature shocks between the day and the night could be the cause,” said Delbo.
Same image as above, but with the fractures highlighted in red. Credit: NASA/Goddard/University of Arizona
Delbo and his colleagues measured the length and angles of more than 1,500 fractures in OSIRIS-REx images by hand: some shorter than a tennis racket, others longer than a tennis court. They found the fractures predominantly align in the northwest-southeast direction, indicating they were caused by the Sun, which is shown here to be the primary force changing Bennu’s landscape.
“We were surprised to learn that the aging and weathering process on asteroids happens so quickly, geologically speaking.” — Marco Delbo
“If landslides or impacts were moving boulders faster than the boulders were cracking, the fractures would point in random directions,” said Delbo.
The research team used a computer model and their fracture measurements to calculate the 10,000- to 100,000-year timeframe for thermal fractures to propagate and split rocks.
“The thermal fractures on Bennu are quite similar to what we find on Earth and on