La NASA découvre des astéroïdes vieillis tôt par le soleil – “Nous avons été surpris”

Récemment, des scientifiques de La mission OSIRIS-REx de la NASA découvert que la régénération de surface se produit sur les astéroïdes beaucoup plus rapidement que sur Terre. En analysant des images haute résolution de fractures rocheuses sur l’astéroïde Bennu prises par le

” data-gt-translate-attributes=”[{” 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 <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="

” data-gt-translate-attributes=”[{” attribute=””>Nature Geoscience. “We were surprised to learn that the aging and weathering process on asteroids happens so quickly, geologically speaking.”

Although landslides, volcanoes, and earthquakes may abruptly alter the Earth’s surface, most changes occur gradually. Over millions of years, water, wind, and temperature changes slowly erode rock to create new surfaces. For instance, if you hiked into the Grand Canyon, you would see distinct rock layers; the top layers tend to be the youngest rocks, dating around 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 chiseling away at rocks in the Grand Canyon for 5 million to 6 million years, according to the U.S. National Park Service.

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.

“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 <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="

” data-gt-translate-attributes=”[{” attribute=””>Mars in terms of how they form,” said Christophe Matonti, a co-author of the paper at Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, Géoazur, Sophia-Antipolis, Valbonne, France. “It is fascinating to see that they can exist and are similar in very ‘exotic’ physical conditions [low gravity, no atmosphere]même comparé à Mars.

“Gardez à l’esprit que la topographie de Bennu est jeune, mais les roches sur les astéroïdes ont encore des milliards d’années et contiennent des informations précieuses sur le début du système solaire”, a déclaré Jason Dworkin, scientifique du projet OSIRIS-REx à Centre de vol spatial Goddard de la NASA à Greenbelt, Maryland.

OSIRIS-REx (Origines, Interprétation Spectrale, Identification des Ressources, Sécurité-Regolith Explorer) renverra un échantillon de Bennu sur Terre le 24 septembre 2023. “Nous pourrons en savoir plus sur l’âge de la surface lorsque nous pourrons étudier directement l’échantillon”, a déclaré Dworkin.

Référence : “Alignement des fractures sur les rochers de Bennu indiquant une évolution rapide de la surface de l’astéroïde” par 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 et Dante S. Lauretta, 23 mai 2022, . Géoscience de la nature.
DOI : 10.1038/s41561-022-00940-3