Asteroids made of ‘rubble’ could be very, very difficult to destroy, astronomers say

Although a common premise in science fiction, the prospect of a large asteroid crashing into Earth is not fiction at all, but rather a guarantee. Extinction asteroids are a periodic event, just like the tides or the full moon; ask the dinosaurs. That’s why the National Aeronautics and Space Administration (NASA) spent so much time and money on the DART (Double Asteroid Redirection Test) mission, which successfully tested our ability to deflect an asteroid from hitting Earth. This mission was a success and suggests (apparently) that asteroids are not as dangerous as one might think.

What if the asteroid in question was virtually indestructible?

According to new research published in the Proceedings of the National Academy of Sciences (PNAS), led by planetary scientist Fred Jourdan of Curtin University in Australia, rubble heap asteroids are more durable (and common) than we previously thought, which could change the way scientists think. about potential planetary defense measures. Rubblepile asteroids are a special type of asteroids that, true to their name, are made up of smaller boulder-sized debris and rocks that have fused together under the influence of gravity. These types of asteroids are notoriously diffuse relative to solid rock.

However, if you thought that these piles of rubble were, due to their composition, fragile and easily broken, you would be wrong.

In the study, Jourdan and his colleagues examined the origin, composition and durability of rubble heap asteroids through the Japan Space Agency’s (JAXA) Hayabusa 1 probe sample return mission.

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As you may remember, JAXA collected samples from an asteroid named Itokawa in 2005 – and despite many setbacks to get them back to Earth – they succeeded in 2010. More than a decade later, in Using a technique called electron backscatter diffraction, Jourdan and his team were able to determine if the particles sent back from Itokawa had ever been impacted in space. Through this process of scanning the surface of the particles, the researchers concluded that these asteroids are nearly indestructible, thanks to a unique “cushion”-like feature.

“Asteroids are usually thought of as one big solid piece of rock, but not all of them are like that – some are called rubble piles because they are rocks, boulders and pebbles clumped together, but there are many empty spaces between these rocks and that extra empty space makes them shock absorbent,” Jourdan told Salon via email. “Rubblepile asteroids like Itokawa are like a giant space cushion.”

Jourdan further explained that the cushions are soft because they contain a lot of air.

“So it’s good to absorb shock, isn’t it?” said Jourdan. “Same for rubble heap asteroids, they’re just good for absorbing shock.”

This new discovery could be why the team of researchers discovered that Itokawa is so old – around 4.2 billion years old, almost the same age as our own solar system.

“We were surprised,” Jourdan said of the asteroid’s age. “Most models predict that an asteroid a few hundred meters to a few kilometers in size should survive ambient bombardment in the asteroid belt for a few hundred million years – yet Itokawa survived more than 4 .2 billion years, much longer than we thought it would be.”

Jourdan said the most important implication of his research is that rubble-pile asteroids are “resistant to bombardment.” While it may seem like we Earthlings are doomed in terms of planetary defense, he said we can “use this to our advantage.”

As for the 2022 DART mission, NASA sent a 1,320-pound spacecraft to crash into a small asteroid called Dimorphos and throw it out of orbit. While the mission was a resounding success, Jourdan said “the problem is that you have to detect asteroids very early because the thrust will be very weak”.

“So if the asteroid starts being pushed by a kinetic impact, say three years before it collides with Earth, no problem; DART-like devices can do that,” Jourdan said. “But what if we don’t have enough time? What if we suddenly find out that an asteroid will impact the Earth within 3 months? What do we do?”

This is where Jourdan’s new research comes in.

“So what we’re suggesting in our study is that we should explore the possibility of detonating a nuclear device very close to the asteroid,” Jourdan said. “Why? Because the shock wave would be much more energetic than small kinetic impactors like DART.”

Jourdan said the fact that rubble heap asteroids are so durable means that the purpose of the explosion would not be to destroy them, but simply to shift their trajectory so that they do not hit Earth.

“Blowing up an asteroid is really not the way to go because all the debris would rain down and cause similar devastation,” he said.