Scientists say some “rubble pile” asteroids are almost impossible to destroy

The researchers said a kind of “hard-to-destroy” asteroid composed of a pile of rocks could require new strategies such as a “nuclear blast” to push it off a trajectory off a potential collision course with Earth.

The study, published Monday in the journal PNAS, looked at three tiny dust particles collected from the surface of an ancient 500-meter-long asteroid called Itokawa.

Analysis of these dust particles, returned to Earth by Japan’s Jaxa space agency’s Hayabusa 1 probe, suggests that the asteroid may be almost as old as the solar system itself.

Scientists, including those at Curtin University in Australia, found that Itokawa – about two million kilometers from Earth and the size of the Sydney Harbor Bridge – was nearly impossible to destroy.

Last year, NASA showed in a proof of concept test of the Dart mission that it is likely possible to successfully move an Earth-threatening asteroid before it hits the planet with the spacecraft.

But a new study indicates that changing the trajectory of an asteroid like Itokawa, made of a pile of debris and dust, can be “very difficult” by hitting it with a spacecraft.

“Unlike monolithic asteroids, Itokawa is not a single lump of rock, but belongs to a family of rubble heaps, meaning it is entirely made of loose boulders and rocks, almost half of which is empty space,” said study co-author, Fred Jordan.

“The survival time of Itokawa-sized monolithic asteroids is predicted to be only a few hundred thousand years in the asteroid belt,” said Dr Jourdan.

Scientists are calling for testing new strategies to push debris asteroids like Itokawa out of the trajectory of a potential impact with Earth.

“If the asteroid is detected too late for the kinetic push, we could potentially use a more aggressive approach, such as using the shockwave of a nearby nuclear blast to push a pile of debris off course without destroying it,” said Nick Timms, co-author of the study.

The researchers said the impact that destroyed the asteroid’s host rock and formed Itokawa probably occurred at least 4.2 billion years ago.

The study suggests that the long survival time of an Itokawa-sized asteroid may be due to the shock-absorbing nature of the material that makes up the debris pile.

“In short, we found Itokawa to be like a giant space cushion and very difficult to destroy,” Dr Jourdan explained.

The study used two complementary techniques to analyze the three dust particles: one method measured whether the space rock was shocked by a meteorite impact, and the other was used to date asteroid impacts.

The persistence of such debris asteroids was previously unknown.

According to the researchers, the latest discovery “compromises” the ability to design strategies in case such an asteroid flies towards Earth.

“Now that we’ve discovered that they can survive in the solar system for almost its entire history, they must be more numerous in the asteroid belt than previously thought, so there’s a higher chance that if a large asteroid is heading towards Earth, it will be a poop debris,” Dr Timms added.

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