Itokawa (minor planet 25143)

Image of Itokawa taken by Hayabusa from a range of about 20 km

A small asteroid that was the target of the Japanese Hayabusa (MUSES-C) probe – the first spacecraft to return a sample of material from an asteroid. 25143 Itokawa, also known as 1998 SF36, was discovered by LINEAR in 1998 and is named after the late Hideo Itokawa, considered one of the fathers of Japan's space program. It is both an Apollo asteroid and a Mars-crosser and appears to have an S-class composition.

The first images of Itokawa returned by Hayabusa proved surprising. The asteroid's shape – similar to a knobbly potato – is not what researchers had predicted based on radar images. Another asteroid mission, NASA's NEAR-Shoemaker, visited the asteroid Eros in 2000 and found it to be fairly homogenous. This does not appear to be the case for Itokawa. Early pictures of the asteroid appear to show hilly and rocky regions in addition to some very smooth features. Itokawa's edges appear rounded, possibly the result of eons of being pelted by other space objects. There also appears to be some dust and rocks left over from impacts on the asteroid's surface. This is another surprise because small asteroids, with such a small gravitational pull, were not expected to havemuch in the way of regolith. It is strongly suspected from its appearance that Itokawa may be a rubble-pile asteroid.

dimensions	0.687 × 0.287 × 0.264 km
mass	~4.8 × 10¹⁰ kg
spectral class	S
rotational period	12.5 hours
albedo	0.53
semimajor axis	1.324 AU
perihelion	0.953 AU
aphelion	1.695 AU
eccentricity	0.280
inclination	1.62°
orbital period	556.36 days

Related category

• NOTABLE ASTEROIDS, CENTAURS, AND KUIPER BELT OBJECTS

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