‘Rubblepile’ asteroids nearly impossible to destroy, study finds

Asteroid discoveries from space dust particles could save the planet

The Itokawa asteroid. Credit: Curtin University

Research by Curtin University into the durability and age of an ancient asteroid made of rocky rubble and dust has revealed important findings that could potentially help save the planet if it were ever rushed back to Earth.

The international team studied three tiny dust particles collected from the surface of the 500-metre-long ancient rubble-pile asteroid Itokawa, beamed back to Earth by the Japanese Space Agency’s Hayabusa 1 probe.

The results of the study showed that the asteroid Itokawa, located 2 million kilometers from Earth and the size of the Sydney Harbor Bridge, was difficult to destroy and resistant to collisions.

Lead author Professor Fred Jourdan, director of the Western Australian Argon Isotope Facility, part of the John de Laeter Center and Curtin’s School of Earth and Planetary Sciences, said the team also found that Itokawa is almost as old as the solar system itself.

“Unlike monolithic asteroids, Itokawa is not a single piece of rock, but belongs to the family of rubble heaps, which means that it consists entirely of boulders and loose rocks, almost half of which is an empty space,” Professor Jourdan said.

“The survival time of Itokawa-sized monolithic asteroids is only expected to be several hundred thousand years in the asteroid belt.

“The huge impact that destroyed Itokawa’s monolithic parent asteroid and formed Itokawa occurred at least 4.2 billion years ago. Such a surprisingly long survival time for an asteroid the size of ‘Itokawa is attributed to the shock-absorbing nature of the rubble pile material.

“In short, we found that Itokawa is like a giant space cushion, and very difficult to destroy.”

Asteroid discoveries from space dust particles could save the planet

Itokawa grain with scale. Credit: Celia Mayers/Curtin University

The Curtin-led team used two complementary techniques to analyze the three dust particles. The first is called Electron Backscattered Diffraction and can measure if a rock has been shocked by a meteor impact. The second method, argon-argon dating, is used to date asteroid impacts.

Co-author, Associate Professor Nick Timms, also from Curtin’s School of Earth and Planetary Sciences, said the durability of rubble-pile asteroids was previously unknown, undermining the ability to devise defense strategies in case the would rush towards Earth.

“We wanted to find out if rubble-pile asteroids are resilient to shocks or if they splinter on the slightest shock,” said Associate Professor Timms.

“Now that we’ve discovered that they can survive in the solar system for most of its history, they must be more abundant in the asteroid belt than previously thought, so there’s a better chance that if a big asteroid is rushing towards Earth, it will be a pile of rubble.

“The good news is that we can also use this information to our advantage – if an asteroid is detected too late for a kinetic push, then we can potentially use a more aggressive approach like using the shock wave from a nearby nuclear explosion to push an asteroid into a pile of rubble has veered off course without destroying it.”

Co-authors from Curtin University include Associate Professor William Rickard, Celia Mayers, Professor Steven Reddy, Dr David Saxey and Distinguished Professor John Curtin Phil Bland, all from the School of Earth and Planetary Sciences .

Posted in the Proceedings of the National Academy of Sciencesthe study is titled “Rubblepile Asteroids Are Forever”.

More information:
Jourdan, Fred, rubble heap asteroids are forever, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2214353120.

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Curtin University

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