Asteroid discovery could assist with planetary defence strategies

In a Curtin University-led study into the durability and age of an ancient asteroid, potential ways to save the planet if one ever hurtled toward Earth have been revealed.

The team of researchers studied three tiny dust particles, collected by the Japanese Space Agency’s Hayabusa 1 probe, from the surface of the asteroid Itokawa – an ancient 500-metre-long rubble pile asteroid. The results revealed that Itokawa, which is two million kilometres from Earth, was hard to destroy and resistant to collision. It was found that the asteroid is also almost as old as the solar system itself.

The research, titled ‘Rubble Pile Asteroids are Forever,’ is published in the Proceedings of the National Academy of Sciences.

Itokawa has a large survival time due to its shock-absorbent nature

Lead author Professor Fred Jourdan, Director of the Western Australian Argon Isotope Facility, part of the John de Laeter Centre and the School of Earth and Planetary Sciences at Curtin, said: “Unlike monolithic asteroids, Itokawa is not a single lump of rock, but belongs to the rubble pile family which means it’s entirely made of loose boulders and rocks, with almost half of it being empty space.

“The survival time of monolithic asteroids the size of Itokawa is predicted to be only several hundreds of thousands of years in the asteroid belt.

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

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

The durability of rubble pile asteroids was previously unknown

Two complementary techniques were used to analyse the three dust particles: Electron Backscattered Diffraction, which can measure if a rock has been shocked by any meteor impact, and argon-argon dating, which is used to date asteroid impacts.

© shutterstock/Alexyz3d

Associate Professor Nick Timms, also from Curtin’s School of Earth and Planetary Sciences and co-author of the study said that the durability of rubble pile asteroids was previously unknown. This threatened the ability to design potential defence strategies if one was to hurtle towards Earth.

“We set out to answer whether rubble pile asteroids are resistant to being shocked or whether they fragment at the slightest knock,” Associate Professor Timms said.

“Now that we have found they can survive in the solar system for almost its entire history, they must be more abundant in the asteroid belt than previously thought, so there is more chance that if a big asteroid is hurtling toward Earth, it will be a rubble pile.

“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, we can then potentially use a more aggressive approach like using the shockwave of a close-by nuclear blast to push a rubble-pile asteroid off course without destroying it.”

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