What Itokawa's dust told us about meteorites — and water

How 1,500 tiny grains linked the most common meteorites to S-type asteroids and revealed surprising water.

Published 2026-10-23

Hayabusa's capsule carried only tiny specks of Itokawa — JAXA identified about 1,500 rocky grains.^[5] They have had an outsized impact on planetary science.

Solving a meteorite mystery

The most common meteorites to fall on Earth are ordinary chondrites, and the most common asteroids in the inner main belt are S-type asteroids like Itokawa. The Itokawa grains confirmed the long-suspected link: S-type asteroids are a source of ordinary chondrites.^[1] Itokawa's composition specifically matches the LL group (low total iron, low metal).^[4]

Evidence of a lost parent body

Many grains show signs of slowly cooling after forming deep inside a rocky body at about 800 °C. That would require a parent body more than 20 km across — far larger than Itokawa's half-kilometer length. Itokawa is likely what remains of a much larger object shattered by a collision.^[1]

Weathered by space

Dust collected from the surface appears to have been exposed there for about eight million years.^[4]

Water from a “dry” asteroid

In 2018, two separate research groups reported water in Itokawa particles, including in grains of the mineral pyroxene. The estimated water content suggested Itokawa's parent had once been a water-rich asteroid.^[4] Later studies found water and hydroxide formed on grain surfaces, consistent with hydrogen from the solar wind combining with oxygen in the minerals — a possible source of some of Earth's water.^[4]

Explore the sky yourself

You can't see Itokawa without a large telescope, but a good pair of binoculars opens up the Moon, star clusters and the Milky Way. Our binocular picker can help you choose.

Numbered citations link to the sources list on the Itokawa overview page.