Itokawa
Key facts
- What it is
- Near-Earth asteroid (Apollo group)
- Size
- About 535 m long
- Discovered
- 1998
- Spacecraft
- Hayabusa (2005); samples returned 2010
- Orbit group
- Apollo
- Average distance from the Sun
- 1.32 au (about 200 million km)
- Time to go round the Sun
- 556 days
- Closest and farthest from the Sun
- 0.95 to 1.7 au
- Tilt of its orbit
- 1.6°
- Closest its orbit comes to Earth's
- 1,900,000 km (5.1 times the Moon's distance)
- Spins once every
- 12.1 hours
An au (astronomical unit) is Earth's average distance from the Sun, about 150 million km. Orbit figures are from open tracking data, figures last updated 1 Nov 2026.
Itokawa was the first asteroid from which samples were brought back to Earth. Japan's Hayabusa spacecraft arrived in September 2005, studied the asteroid for about two months and touched down briefly in November. After a difficult journey home with failing engines, its capsule landed in the Australian outback in June 2010.
Itokawa is small, only about 535 metres long, and shaped like a sea otter or a peanut, with a larger body and a smaller head. The images were a surprise. There were very few craters, and the surface was a jumble of boulders with smooth areas of gravel in the low places. Its density is low for a stony body, so Itokawa must be a rubble pile, a loose heap of fragments held together only by its weak gravity, rather than a single solid rock.
The capsule contained about 1,500 tiny grains, most smaller than the width of a hair, picked up when the spacecraft touched the surface. Their analysis solved a long-standing puzzle. S-type asteroids are the most common kind in the inner belt, but their colour did not quite match the most common meteorites, the ordinary chondrites. Itokawa's grains turned out to be LL chondrite material, proving the link and showing that the mismatch in colour is caused by space weathering: the slow darkening and reddening of surfaces exposed to the solar wind and micrometeorite impacts.
The asteroid was discovered in 1998 by a survey telescope in New Mexico and named after Hideo Itokawa, a pioneer of Japanese rocketry.
Coming close to Earth
Its next passes within about 30 million km of Earth, worked out from its orbit. Each one is a safe miss.
| Date | Distance | In Moon distances |
|---|---|---|
| 23 Mar 2033 | 13,000,000 km | 33 |
| 11 Jun 2036 | 6,100,000 km | 16 |
| 17 Jul 2039 | 28,000,000 km | 72 |
| 9 Apr 2071 | 4,100,000 km | 11 |
| 5 Jul 2074 | 7,000,000 km | 18 |
| 21 Mar 2100 | 19,000,000 km | 50 |