Three specks of dust reveal the secrets of an asteroid

published on Monday, January 23, 2023 at 9:56 p.m.

The grains are tiny, smaller than the thickness of a hair, but they hold the history, in billions of years, of the secrets of an asteroid.

The three particles from the Itokawa asteroid revealed that this type of space object is much older than imagined, and much harder.

This would involve revising plans to avoid a collision with Earth, according to a study published Monday in the journal Proceedings of the US National Academy of Sciences.

The three samples were recovered in 2005 from the asteroid, while it was cruising some 300 million kilometers from Earth. The Japanese space probe Hayabusa took five years to bring them back to the blue planet, along with hundreds of other particles from Itokawa.

Fred Jourdan, a professor at the College of Earth and Planetary Sciences at Australia’s Curtin University, sought to find out the age of Itokawa, a type of asteroid said to have a “loose cluster”.

It results from the assembly of the fragments of a monolith asteroid which was pulverized by a shock.

Monolith asteroids are said to have a lifetime of a few hundred million years, and to be gradually eroded by collisions with other asteroids.

The loose cluster asteroid, like Itokawa, has a much different structure. With a motley collection of rocks, dust, gravel and even vacuum, held together by a simple effect of gravity.

“It’s like a giant cushion in space, and cushions are good at absorbing shocks,” remarks Professor Jourdan.

To find out just how much, the team analyzed the crystal structure of the samples, looking for deformations from the impact that created Itokawa. And also dated them.

The conclusion is that Itokawa was formed after a collision that occurred at least 4.2 billion years ago, almost the age of the Earth (4.5 billion years), but above all ten times older than the age of monolithic asteroids of similar size.

An age so venerable that Fred Jourdan is “convinced” that some of his colleagues “won’t believe him”.

The resilience of this type of space object to collisions is such that there should be many more of them than previously imagined, according to the study.

With the consequence of adapting the ways to guard against a collision of the Earth by this kind of asteroid, notes the geochemist.

The DART experiment to divert an asteroid’s trajectory, successfully carried out last year by NASA, shows that this is possible with an object like Itokawa, again according to the scientist. But this would require applying a much greater force to it, for example with a nuclear warhead, so that “the shock wave deflects the asteroid from its course”.

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