How three specks of dust reveal the secrets of an asteroid

The spots are tiny. No, really tiny. Smaller than the diameter of a hair. But they have billions of years of history that reveal some asteroid secrets.

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

And that could mean we need bolder ways to prevent catastrophic collisions with Earth, according to research published Tuesday.

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

The Japanese spacecraft Hayabusa took five years 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 at Curtin University’s School of Geosciences and Planetary Sciences, wanted to see what the spots could tell about the age of debris piles of asteroids like Itokawa.

They are formed when solid asteroids collide and the resulting fragments coalesce into new structures.

Solid asteroids are thought to have lifetimes of several hundred million years and are gradually destroyed by constant collisions.

But rubble-pile asteroids have a very different structure, composed of rock, dust, pebbles, and void, and held together by the gravitational pull of their various constituents.

“It’s like a giant space cushion, and the cushions absorb shock well,” Jourdan said.

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

They dated the samples by measuring the decay of potassium into argon.

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

“We were really surprised,” said Jourdan.

“I mean, it’s really, really old, and I’m sure some of my colleagues won’t even believe it.”

Debris-pile asteroids are so resilient to the constant impacts they come in contact with that they are likely to be many more than previously thought, concludes a study published in the journal Proceedings of the National Academy of Sciences.

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

NASA’s recent DART test showed that asteroids like Itokawa could be swerved off course, but it would likely take several years of implementation.

An asteroid just weeks away from colliding with Earth would require a different approach, and Jourdan says a nuclear blast may be needed.

“It’s not like Armageddon,” he adds, referring to the 1998 science-fiction film.

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

Drawing far-reaching conclusions from such tiny dust particles, however, is an analysis of each particle at the atomic level.

“We can get such big stories from (something) very, very small because these machines, what they do is measure and count atoms,” Jourdan said.

“Each seed has its own story to tell.”


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