Dust grains reveal asteroid Itokawa’s age

On June 13, 2010, Japan’s asteroid-visiting Hayabusa spacecraft earned its name (“peregrine falcon”) by divebombing through Earth’s atmosphere at 7.5 miles (12.2 kilometers) per second.

As expected, the spacecraft disintegrated upon re-entry; however, a heat-shielded sample-return capsule survived the fall relatively unscathed, returning a plethora of precious dust grains collected from the loosely bound asteroid known as Itokawa.

Hayabusa spacecraft
Hayabusa spacecraft

After nearly a decade of closely examining the samples returned by Hayabusa, a study published August 7 in Scientific Reports claims to have finally pinned down the origins of the mysterious near-Earth asteroid. Based on analysis of more than a thousand specks of dust from Itokawa, scientists have learned that the primeval pile of rubble formed some 4.6 billion years ago, right around the time the solar system was born. However, unlike some asteroids, Itokawa apparently has had an eventful life since then. According to the study, about 1.5 billion years ago, a run-in with another asteroid nearly obliterated Itokawa before the remains eventually re-accreted into its present-day form.

A close-up view of a microscopic dust grain from asteroid Itokawa, which was collected by Japan’s Hayabusa spacecraft
A close-up view of a microscopic dust grain from asteroid
Itokawa, which was collected by Japan’s Hayabusa spacecraft

Furthermore, the researchers say Itokawa spent most of its life (and death and rebirth) in the asteroid belt, and it was kicked out into its current near- Earth orbit only in the past couple hundred thousand years. And since asteroids don’t typically fare well outside the main belt, the researchers predict Itokawa will either break apart or collide with Earth within the next million years. As Hayabusa showed, asteroid return missions can result in fascinating discoveries. With Hayabusa2 and OSIRIS-REx now underway, researchers should soon have a wealth of material to analyze, helping them methodically piece together the complicated history of these cosmic bocce balls.