Scientists ‘surprised’ to find that Sun ages some asteroids much sooner than earlier thought

“Surprised” scientists have discovered that the Sun’s heat likely fractures rocks on asteroid Bennu in only 10,000-100,000 years, an advance suggesting space rocks age more rapidly than earlier thought.

High-resolution images of rock fractures on asteroid Bennu taken by the Osiris-Rex spacecraft were analysed by researchers, said the study, published recently in the journal Nature Geoscience.

The Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (Osiris-Rex) spacecraft left Bennu’s orbit in May 2021 and is expected to reach Earth in the latter half of 2023.

Using data from the spacecraft, researchers, including those from CNRS in France, could 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.

“We were surprised to learn that the aging and weathering process on asteroids happens so quickly, geologically speaking... we thought surface regeneration on asteroids took a few millions of years,” study co-author Marco Delbo from the Université Côte d’Azur in France said in a statement.

Researchers said landslides, volcanoes and earthquakes gradually change the surface on Earth, along with other forces like water, wind and temperature changes chipping down rock layers and creating new surfaces over millions of years.

On the asteroid Bennu, where the Sun rises every 4.3 hours, rapid temperature changes create internal stress that fractures and breaks down rocks, similar to how a cold glass breaks under hot water.

The Nasa spacecraft Osiris-Rex spotted cracks in the rocks in its first surveys of the asteroid.

Researchers said 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”.

Scientists then measured the length and angles of more than 1,500 fractures in Osiris-Rex images by hand – some shorter than a tennis racket and others longer than a tennis court.

They found the fractures predominantly align in the northwest-southeast direction, meaning they were likely caused by the Sun, which could be the primary force changing Bennu’s landscape, the study noted.

“If landslides or impacts were moving boulders faster than the boulders were cracking, the fractures would point in random directions,” Dr Delbo said.

Researchers used a computer model to calculate the 10,000- to 100,000-year timeframe for thermal fractures to propagate and split rocks on the asteorid.

“The thermal fractures on Bennu are quite similar to what we find on Earth and on Mars in terms of how they form.

“It is fascinating to see that they can exist and are similar in very ‘exotic’ physical conditions [low gravity, no atmosphere], even compared to Mars,” Christophe Matonti, another co-author of the study, said.

While the topography of Bennu is young, researchers highlight that the rocks on the asteroids are still billions of years old and “hold valuable information about the beginning of the solar system”.

Scientists hope that when the Osiris-Rex asteroid returns a sample from Bennu to Earth in 2023, they could learn more about the age of the surface and how the space rock has evolved.

Scientists had earlier calculated the 500m-long asteroid could make a close approach to Earth in 2135.

If Bennu slammed Earth, it wouldn’t wipe out life, but make a crater roughly 10-20 times the size of the asteroid, Lindley Johnson, Nasa’s planetary defense officer, had said last year.