Asteroid

Itokawa

The small rubble-pile asteroid from which Japan's Hayabusa returned the first asteroid sample in 2010, linking common meteorites to their source.

A radar shape model of Itokawa
Image: S. J. Ostro et al., NASA/JPL (radar shape model)

At a glance

Next close approach
Mar 23, 2033 (UTC) · 33 lunar distances
Size
~500 m long rubble pile
Impact risk
Not on NASA's impact-risk list
Close approaches and the impact-risk list

Missions to Itokawa

From discovery to the flyby

  1. May 9, 2003
    Launch on an M-V rocket from Uchinoura
    Hayabusa
  2. May 2004
    Earth swing-by
    Hayabusa
  3. September 12, 2005
    Arrives at asteroid Itokawa
    Hayabusa
  4. November 20, 2005
    First touchdown on Itokawa
    Hayabusa
  1. November 25, 2005
    Second touchdown on Itokawa
    Hayabusa
  2. April 2007
    Leaves Itokawa for Earth
    Hayabusa
  3. June 13, 2010
    Returns the Itokawa sample to Earth, the first asteroid sample
    Hayabusa

Itokawa is the first asteroid from which samples were collected and brought to Earth.[1] The dust that Japan's Hayabusa spacecraft returned in 2010 settled a long-standing question: where the most common meteorites come from.[1]

A small rubble pile

Itokawa was discovered on 26 September 1998 by the Lincoln Near-Earth Asteroid Research team at Socorro, New Mexico.[1] It is named for Hideo Itokawa, regarded as the father of Japanese rocketry, who led Japan's first rocket launch tests in 1955.[1] Its longest dimension is only about 0.5 km, about five football fields end to end.[1]

Itokawa is not a solid rock but a rubble pile, a collection of rocks loosely held together by their own weak gravity.[1] It has few craters, probably because any impact strong enough to make one shakes loose rocks that fill it in.[1] Its two-lobed shape, which the mission team compared to a sea otter, may come from two rubble piles that drifted together and stuck.[1]

Hayabusa's mission

Hayabusa launched on 9 May 2003 and reached Itokawa on 12 September 2005, after a journey of two billion km.[2] It touched down twice, on 20 and 25 November 2005, and collected a small amount of dust even though the mechanism designed for the purpose failed.[2][1] Its capsule returned to Earth on 13 June 2010 and was recovered at Woomera, in Australia.[2]

What the dust showed

The grains matched LL chondrites, a group of ordinary chondrites, which are the most common kind of meteorite found on Earth.[2][1] That confirmed that S-type asteroids like Itokawa, the most common type in the inner asteroid belt, are a source of those meteorites.[1]

The grains also preserve Itokawa's history. Many had cooled slowly after forming deep inside a rocky body at around 800 °C, which requires a parent body more than 20 km across.[1] Itokawa is therefore thought to be reassembled debris from a much larger asteroid shattered by a collision.[1] Its largest boulder, about 50 m across, is thought to be a fragment of that event.[1] Hayabusa's successor, Hayabusa2, went on to collect samples from the asteroid Ryugu.[3]

Sources

  1. [1]NASA, 25143 Itokawa — science.nasa.gov, retrieved October 26, 2026
  2. [2]JAXA Extraterrestrial Sample Curation Center, Hayabusa and Itokawa — curation.isas.jaxa.jp, retrieved October 26, 2026
  3. [3]JAXA, Asteroid Explorer Hayabusa2 — global.jaxa.jp, retrieved October 26, 2026

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