By Rani C. Gran, NASA Goddard Space Flight Center July 24, 2022
This mosaic of asteroid Bennu was created using observations made by NASA’s OSIRIS-REx spacecraft that flew very close to the asteroid for more than two years. Credit: NASA/Goddard/University of Arizona
Recently, scientists on NASA’s OSIRIS-REx mission discovered that surface regeneration occurs on asteroids much faster than on Earth. By analyzing high-resolution images of rock fractures on asteroid Bennu taken by the OSIRIS-REx spacecraft, the researchers discovered that the Sun’s heat fractures Bennu’s rocks in just 10,000 to 100,000 years. Using this knowledge, scientists will be able to better predict how long it takes for rocks from asteroids like Bennu to break up into smaller pieces, some of which may be released into space while others may remain in the asteroid surface.
Although tens of thousands of years might seem quite slow, “we thought that the surface regeneration of asteroids took a few million years,” said Marco Delbo, senior scientist at the Université Côte d’Azur, CNRS, Observatoire de the Côte d’Azur, Laboratoire. Lagrange, Nice, France, and lead author of a paper published in June 2022 in the journal Nature Geoscience. “We were surprised to learn that the aging and weathering process of asteroids occurs so rapidly, geologically speaking.”
Although landslides, volcanoes, and earthquakes can alter Earth’s surface abruptly, most changes occur gradually. Over millions of years, water, wind and temperature changes slowly erode the rock to create new surfaces. For example, if you hiked the Grand Canyon, you would see different layers of rock; the upper layers are usually the youngest rocks, about 270 million years old, and the layers at the bottom of the canyon are the oldest, about 1.8 billion years old. The Colorado River has been carving the rocks of the Grand Canyon for 5 to 6 million years, according to the US National Park Service.
PolyCam aboard NASA’s OSIRIS-REx spacecraft provided high-resolution, microscope-like images of the surface of asteroid Bennu. This allowed the 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 cracks rocks, comparable to how a cold glass breaks under hot water. In Bennu, the Sun rises every 4.3 hours. At the equator, daytime highs can reach nearly 260°F (about 127°C) and nighttime lows drop to almost minus 10°F (about minus 23°C).
OSIRIS-REx scientists spotted cracks in the rocks in spacecraft images from early surveys of the asteroid. All the fractures seemed to point in the same direction, “a clear signature that temperature shocks between day and night could be the cause,” Delbo said.
The same image as the previous one, but with the fractures highlighted in red. Credit: NASA/Goddard/University of Arizona
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.
“We were surprised to learn that the aging and weathering process of asteroids occurs so rapidly, geologically speaking.” – Marco Delbo
“If landslides or impacts moved the rocks faster than the cracks, the fractures would point in random directions,” Delbo said.
The research team 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 Côte d’Azur, CNRS, Observatoire de la Côte. d’Azur, Géoazur, 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.”
“Keep in mind that Bennu’s topography is young, but the asteroid rocks are still billions of years old and contain valuable information about the early solar system,” said Jason Dworkin, OSIRIS-REx project scientist at NASA’s Goddard Space. Flight Center in Greenbelt, Maryland.
OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) will return a sample of Bennu to Earth on September 24, 2023. “We will be able to learn more details about the age of the surface when we can. study the sample directly,” Dworkin said.
Reference: “Alignment of fractures on Bennu’s boulders indicative of rapid asteroid surface evolution” by Marco Delbo, Kevin J. Walsh, Christophe Matonti, Justin Wilkerson, Maurizio Pajola, Manar M. Al Asad, Chrysa Avdellidou, Ronald-Louis Ballouz, Carina A Bennett, Harold C. Connolly Jr., Daniella N. DellaGiustina, Dathon R. Golish, Jamie L. Molaro, Bashar Rizk, Stephen R. Schwartz, and Dante S. Lauretta, 23 May 2022, Nature Geoscience.DOI: 10.1038/ s41561 -022-00940-3