Sun's Heat Speeds Up Ageing And Weathering On Asteroids Like Bennu, NASA Says

The team of scientists analysed the rock fractures visible on the asteroid from the images, and discovered that the Sun's heat fractures rocks on the asteroid in just 10,000 to 100,000 years.

Surface regeneration takes place a lot quicker on asteroids than on Earth, scientists from NASA's OSIRIS-REx mission have found. The OSIRIS-REx spacecraft has captured high-resolution images of the asteroid Bennu. The team of scientists analysed the rock fractures visible on the asteroid from the images, and discovered that the Sun's heat fractures rocks on the asteroid in just 10,000 to 100,000 years. In other words, the Sun's heat speeds up ageing and weathering on asteroids like Bennu.

The fact that the Sun's heat fractures rocks on Bennu in just a few thousand years allows scientists to estimate how long it takes boulders on asteroids like Bennu to break down into smaller particles. The smaller particles may either eject into space or stay on the asteroid's surface.

The study describing the findings was recently published in the journal Nature Geoscience. 

Ageing On Asteroids Happens ‘Quickly’: Study Author

In a statement released by NASA, Marc Delbo, the lead author on the paper, said tens of thousands of years might sound pretty slow, but scientists thought surface regeneration on asteroids took a few millions of years. He said the researchers were surprised to learn that the ageing and weathering process on asteroids happens so quickly, geologically speaking.

Rock layers are slowly broken down by factors such as water, wind, and temperature changes. As a result, new surfaces are formed over millions of years. According to NASA, if one hikes into the Grand Canyon, they would see distinct Rick layers. In the Grand Canyon, the top layers represent the youngest rocks, and are around 270 million years old. The layers at the bottom of the Grand Canyon are believed to be the oldest, about 1.8 billion years old. 

The Colorado River has been carving down rocks in the Grand Canyon for five million to six million years, according to the US National Park Service. 

What Fractures The Rocks On Bennu?

Since the temperatures on Bennu change rapidly, internal stress is created. This internal stress fractures and breaks down the rocks. NASA compares internal stress fracturing the rocks to hot water breaking down a cold glass. 

The Sun rises every 4.3 hours on Bennu, and daytime highs at the equator can reach almost 260 degrees Fahrenheit. Meanwhile, the nighttime lows can plummet to nearly minus ten degrees Fahrenheit.

The OSIRIS-REx images from the first surveys of the asteroid show cracks in the rocks. 

According to Delbo, the fractures in the rocks indicate a distinct signature that temperature shocks between the day and the night could be the cause.

According to NASA, the researchers measured the length and angles of more than 1,500 fractures in OSIRIS-REx images by hand. Some fractures were shorter than a tennis racket, and others were longer than a tennis court. Since most of the fractures aligned in the northwest-southeast direction, the study authors concluded that the fractures were caused by the Sun.

Delbo said that if landslides or impacts were moving boulders faster than the boulders were cracking, the fractures would point in random directions.

Christophe Matonti, a co-author on the paper, said the thermal fractures on Bennu are quite similar to what "we find on Earth and on Mars in terms of how they form". 

Jason Dworkin, OSIRIS-REx project scientist at NASA's Goddard Space Flight Center in Greenbelt, said the topography of Bennu is young, but the rocks on the asteroids are still billions of years old and hold valuable information about the beginning of the solar system.

The damage due to this space-weathering process has consequences for the material properties of these asteroids, the authors noted in the study.