Although a common premise in science fiction, the possibility of a large asteroid crashing into Earth is not a fantasy at all, but a guarantee. An asteroid extinction event is a periodic event, just like a tidal wave or a full moon. Just ask the dinosaurs. That’s why the National Aeronautics and Space Administration (NASA) spent so much time and money testing the double asteroid redirection. (dart) importantwhich successfully tested our ability to defragment the asteroid from hitting the ground. That mission was a success, and indicates (it seems) that asteroids are not as dangerous as one might think.
But what if the asteroid in question is nearly indestructible?
According to new research published in Proceedings of the National Academy of Sciences (PNAS), led by planetary scientist Fred Jordan of Curtin University in Australia, rubble pile asteroids are more durable (and common) than previously thought, which could change the way scientists think about potential planetary defense measures. Rubble pile asteroids are a special type of asteroid that, true to their name, consist of small pieces of debris the size of boulders and boulders that have clumped together under the influence of gravity. These types of asteroids are notoriously diffuse compared to solid rock.
However, if you think that these piles of rubble are, by virtue of their composition, weak and easily dismantled, you would be mistaken.
In the study, Jordan and colleagues looked at the origin, composition, and durability of rubble-pile asteroids thanks to the Japan Aerospace Agency’s (JAXA) Hayabusa 1 probe sample-return mission.
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As you may remember, JAXA collected samples from an asteroid called Itokawa in 2005—and despite several setbacks to return them to Earth—they succeeded in 2010. A decade later, using a technique called electron backscattering diffraction, Jordan and his team were able to determine whether Particles returning to Itokawa had previously impacted in space. Through a process of scanning the surface of the particles, the researchers concluded that these asteroids are nearly indestructible, thanks to a unique “pillow”-like feature.
“Asteroids are usually thought of as a big chunk of solid rock, but they’re not all like that – some are called cumulus piles because they’re rocks and boulders and pebbles clump together, but there are a lot of voids between those rocks and that extra void makes them shock absorbent,” he said. Jordan to the salon via email. “The rubble-pile asteroids like Itokawa are like a giant space pillow.”
Jordan further explained that the pillows are soft because there is a lot of air trapped in them.
“So it’s a good shock absorber, right?” Jordan said. “Same for rubble heap asteroids, they are only good at absorbing shock.”
This new discovery may be the reason why the team of researchers discovered that Itokawa is very old – estimated to be 4.2 billion years old, which is roughly the same age as our solar system.
“We were surprised,” Jordan said of the asteroid’s age. “Most models predict that an asteroid a few hundred meters to a few kilometers in size should survive surrounding bombardment in the asteroid belt for a few hundred million years – yet Itokawa has survived for over 4.2 billion years; much longer than we thought it would be.”
The most important finding of his research, Jordan said, is that the rubble-pile asteroids are “bombproof”. While this may sound like we Earthlings are doomed in terms of planetary defense, he said we can “use that to our advantage”.
“So what we propose in our study is that we should explore the possibility of detonating a nuclear device very close to the asteroid.”
when it comes to Arrow Mission 2022, 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 huge success, “the problem is that it requires detecting asteroids very early because the thrust would be very small,” Jordan said.
“So if the asteroid starts to be zapped by kinetic impact, say three years before it hits Earth, no problem; DART-like devices can do that,” Jordan said. “But what if we don’t have enough time? What if we suddenly find out that an asteroid is going to hit Earth in 3 months? What do we do?”
This is where Jordan’s new research comes in.
“So what we propose in our study is that we should explore the possibility of detonating a nuclear device very close to the asteroid,” Jordan said. “Why? Because the shock wave will be much more energetic than small kinetic shocks like DART.”
Jordan said that the fact that rubble-pile asteroids are so durable means that the aim of the explosion would not be to destroy them, but merely to nudge their trajectory so that they do not strike Earth.
“An asteroid explosion is not really the right way to go because all the debris will fall off and cause similar destruction,” he said.