Scientists say it’s nearly impossible to destroy some ‘rubble pile’ asteroids

A type of “hard-to-destroy” asteroid, consisting of a pile of rock, may need new strategies, such as a “nuclear explosion”, to push it out of orbit from any potential collision course with Earth, the scientists said.

The research, published Monday in the journal PNAS, examined three tiny dust particles collected from the surface of a 500-metre-long ancient rubble-pile asteroid called Itokawa.

Analysis of these dust particles returned to Earth by the Hayabusa 1 probe of the Japanese Jaxa space agency suggested that the asteroid may be nearly as old as the Solar System.

Scientists, including those from Curtin University in Australia, have discovered that it’s nearly impossible to destroy Itokawa, about two million km from Earth and the size of the Sydney Harbor Bridge.

Last year, Nasa showed in Dart mission proof-of-concept testing that it was likely possible to effectively move an Earth-threatening asteroid before it reaches the planet by colliding with a spacecraft.

But the new study shows that it can be “very difficult” to alter the trajectory of an asteroid like Itokawa, made up of a mound of rubble and dust, by crashing it with a spacecraft.

“Unlike monolithic asteroids, Itokawa is not a single boulder but belongs to the rubble pile family, which means it is composed entirely of loose rocks and boulders, with nearly half of which is empty space,” said study co-author Fred Jourdan.

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

Scientists want new strategies to be tested to push rubble-heavy asteroids like Itokawa out of orbit from a potential collision with Earth.

“If an asteroid is detected too late for the kinetic thrust, then we could potentially use a more aggressive approach, for example using the shock wave of a nearby nuclear explosion to deflect a rubble asteroid off course without destroying it,” said Nick Timms. , co-author of a study.

The impact that destroyed the asteroid’s bedrock and formed Itokawa likely occurred at least 4.2 billion years ago, the researchers said.

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

“In short, we found that Itokawa was like a giant space pillow and very difficult to destroy,” said Dr Jourdan.

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

The durability of such rubble-piled asteroids was previously unknown.

The latest finding, according to the scientists, “compromises” the ability to devise strategies should such an asteroid blast toward Earth.

“Now that we’ve discovered that they can survive nearly all of its history in the solar system, they must be more abundant in the asteroid belt than previously thought, so if a large asteroid shoots toward Earth, there’s a better chance it’s going to be a pile of rubble,” added Dr Timms.

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