Itokawa.space

Near-Earth asteroid (S-type) · Apollo group

Itokawa

(25143) Itokawa · 1998 SF36

A tiny, peanut-shaped rubble pile — and the first asteroid ever to have pieces of its surface brought back to Earth.

Key factsFind your stargazing binoculars
Itokawa at a glance
Object typeNear-Earth asteroid, Apollo group; spectral type S[3]
DiscoveredSeptember 26, 1998 — LINEAR survey, Socorro, New Mexico[3]
Named forHideo Itokawa (1912–1999), “father of Japanese rocketry”[4]
Size≈ 535 × 294 × 209 m (≈ 330 m mean diameter)[3]
ShapePeanut-like — likely a contact binary of two rubble piles[4]
Bulk density≈ 1.9 g/cm³[3]
Rotation period≈ 12.1 hours[3]
Distance from Sun0.95–1.70 AU (average ≈ 1.32 AU)[3]
Orbital period≈ 556 days (1.5 years)[3]
Orbital inclination≈ 1.6°[3]
CompositionMatches LL ordinary chondrite meteorites[1]
Largest boulder≈ 50 m (160 ft) across[1]
SpacecraftJAXA's Hayabusa — arrived September 2005[5]
Sample returnedAbout 1,500 grains, landed in Australia June 13, 2010[5]

Discovery and name

Itokawa was discovered on September 26, 1998, by the LINEAR survey in New Mexico, and received the provisional designation 1998 SF36.[3] It is named in memory of Hideo Itokawa (1912–1999), regarded as the father of Japanese rocketry.[4]

A peanut-shaped rubble pile

Itokawa is tiny: about 535 m long and only about 210 m thick.[3] Hayabusa's science team compared its shape to a sea otter, with a smaller “head” attached to a larger “body.”[1] It is probably a contact binary: two rubble piles that drifted together and stuck.[1][4]

Itokawa is not a solid rock but a rubble pile of boulders and gravel loosely held together by gravity. Few craters are visible, probably because impacts shake loose rocks into any new hole. Its largest boulder is about 50 m across.[1]

Orbit

Itokawa is an Apollo-group near-Earth asteroid: its orbit crosses Earth's. It ranges from about 0.95 to 1.70 AU from the Sun, completing an orbit every 556 days, in an orbit tilted less than 2° to Earth's.[3] It spins once every 12.1 hours.[3]

Sun Earth (1 AU)Mars (1.52 AU) aphelion ≈ 1.70 AU perihelion ≈ 0.95 AU
Top-down orbit of Itokawa to scale, computed from JPL orbital elements (a ≈ 1.32 AU, e ≈ 0.28).[3] Earth and Mars orbits shown for comparison.[6]

Hayabusa: the first asteroid sample return

JAXA's Hayabusa (formerly MUSES-C) launched on May 9, 2003, and reached Itokawa in September 2005.[5] It touched down twice in November 2005, and although its sampling mechanism did not work as designed, it still collected a small amount of dust.[1] After years of struggling with damaged hardware, it returned its capsule to Woomera, Australia, on June 13, 2010.[5] JAXA later identified about 1,500 rocky grains from Itokawa.[5]

Hayabusa was the first mission to return an asteroid sample to Earth for analysis.[5]

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What Itokawa's dust told us

The grains confirmed that S-type asteroids like Itokawa — the most common type in the inner main belt — are the source of the most common meteorites found on Earth, the ordinary chondrites.[1] Some grains show signs of having slowly cooled deep inside a body more than 20 km across, evidence that Itokawa is a remnant of a much larger object shattered by a collision.[1] Surface dust appears to have been exposed for about eight million years, and in 2018 two research groups reported water in Itokawa particles.[4]

Can you see Itokawa?

Not with binoculars or a backyard telescope — at roughly 330 m across, it is far too small and faint.[3] But binoculars are a superb way to start exploring the sky Itokawa travels through: the Moon's craters, bright star clusters and the band of the Milky Way. Try our binocular picker to find a pair that suits you.

Read more

Hayabusa: the comeback mission that brought home the first asteroid sample

A solar flare, failed reaction wheels, a fuel leak and a lost mini-lander — and how JAXA still got a capsule of Itokawa dust to Australia.

Read →

Itokawa, the “sea otter” rubble pile

Why a 535-meter asteroid looks like two pieces stuck together, and what its boulders and missing craters reveal.

Read →

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.

Read →

Sources

  1. 25143 Itokawa — NASA Science
  2. Hayabusa — NASA Science
  3. Small-Body Database Lookup: 25143 Itokawa (1998 SF36) — NASA JPL Solar System Dynamics
  4. 25143 Itokawa — Wikipedia
  5. Hayabusa — Wikipedia
  6. Planetary Fact Sheet (orbit comparison) — NASA NSSDCA

Figures are rounded; where sources differ we note it. Spotted an error? Tell us.