How do three speck of dust reveal an asteroid’s secrets?

The spots are small. No, it’s really small. Smaller than the diameter of a hair. But they have billions of years of history that has revealed some of the secrets of asteroids.

Three-minute particles from an asteroid called Itokawa show that some of these space rocks are much older and much harder than previously thought.

This could mean we need bolder ways to avoid devastating collisions with Earth, according to research published Tuesday.

Three samples were collected in 2005 from Itokawa, which is peanut-shaped about 300 million kilometers (186 million miles) from Earth.

It took five years for the Japanese spacecraft Hayabusa to return them to Earth, along with hundreds of other particles from Itokawa, and scientists have been analyzing them for clues ever since.

Fred Jourdan, a professor in Curtin University’s School of Earth and Planetary Sciences, wanted to see what the speckles could reveal about the age of rubble-piled asteroids like Itokawa.

These are formed when solid asteroids collide and the resulting fragments combine into new structures.

Solid asteroids are thought to have a lifespan of several hundred million years and gradually fall to the ground through constant collisions.

But rubble-piled asteroids have a very different structure, consisting of rocks, dust, gravel, and a vacuum, with their various components held together by the force of gravity.

“It’s like a giant space pillow, and pillows are good at absorbing shock,” Jourdan said.

To find out how good, the team analyzed the crystal structures in the samples, looking for deformations caused by the impact that formed Itokawa.

They dated the samples by measuring the conversion of potassium to argon.

Methods estimate that Itokawa was formed by an asteroid collision at least 4.2 billion years ago, ten times older than solid asteroids of similar size.

“We were really surprised,” Jourdan said.

“So this is really old and I’m sure some of my colleagues won’t even believe it.”

Composed of rubble, asteroids are so resistant to the constant blows they encounter that they are likely in greater numbers than previously thought, according to research published in the Proceedings of the National Academy of Sciences.

This could mean we need new ways to combat such asteroids on a collision course with Earth, Jourdan said.

NASA’s latest DART test has shown that asteroids like Itokawa can be deflected, but this will likely require several years of preparation time.

Just weeks before it collides with Earth, an asteroid may require a different approach, and Jourdan argues that a nuclear explosion may be necessary.

“It’s not ‘Armageddon’ style,” he adds hastily, referring to the 1998 sci-fi movie.

“The shock wave should push the asteroid out of the way.”

Making a conclusion from such tiny dust granules is a far-reaching conclusion, but every particle is analyzed at the atomic level.

“We can make big stories like this out of something very, very small, because what these machines do is measure and count atoms,” Jourdan said.

“Every grain has its own story to tell.”


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