spaceSpace and Physics

Scientists Just Used Ridiculously Tiny Grains Of An Asteroid To Work Out Its Age


Jonathan O'Callaghan

Senior Staff Writer

Itokawa as seen by Hayabusa in 2005. ISAS/JAXA

Scientists have managed to determine the age of an asteroid, thanks to tiny particles of it that were returned to Earth almost a decade ago.

The samples were returned by the Japanese spacecraft Hayabusa, launched in 2003 to visit the asteroid Itokawa. Hayabusa was designed to scoop material from the asteroid and bring it to Earth, but a failure of its collection system meant it only brought back about 1,500 grains, each about 10 micrometers in size.


The mission also experienced an engine failure, limping home years later than planned in 2010. But against all the odds, the tiny sample it collected from the asteroid survived, re-entering our atmosphere in a capsule and being picked up from the South Australian outback.

Now in a paper published in Scientific Reports, scientists from Osaka University in Japan have used that ridiculously small sample to make an interesting finding. They’ve been able to work out how old the Itokawa asteroid is. 

Their findings show that Itokawa comes from an unknown parent asteroid that formed 4.6 billion years ago at the dawn of the Solar System. About 1.5 billion years ago, that parent asteroid crashed into another asteroid and was destroyed, breaking into smaller pieces – including trusty old Itokawa.

“[W]e propose that an intense impact event on Itokawa’s parent body and reassembly occurred within the asteroid main belt and that its by-product, Itokawa, must have spent on the order of thousands of million years in the main belt,” the researchers wrote in their paper.

Dust kicked up by Hayabusa was gathered by its sample collector. Wikimedia

To make the finding, the scientists studied the Itokawa particles returned to Earth and focused on a few micrometers of phosphate materials. They then looked at the amount of lead and uranium in the particles. By noting their decay rate and the crystallization of the phosphate, the scientists were able to pinpoint when the parent asteroid formed and when Itokawa split. Which is pretty amazing.

Almost all of the near-Earth asteroids in our Solar System were formed in a similar way, with a parent body breaking up at some point in the past. We’re doing our best to track back the history of asteroids, but it’s a tricky business.

So working out the history of Itokawa can tell us more about this specific family. And it can tell us more about where asteroids like this come from, and what might become of them in the future.

Itokawa’s future might not be too great for us, mind, with the researchers noting it “will collide with the Earth within a million years and/or be destroyed by space erosion.” Ah.


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