S-type asteroid

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S-type asteroids are of a silicaceous (stony) composition, hence the name. Approximately 17% of asteroids are of this type, making it the second most common after the C-type.

Contents

1 Characteristics
2 S-group asteroids

2.1 SMASS classification
2.2 Tholen classification

3 See also
4 References

Characteristics

S-types are moderately bright (with an albedo of 0.10 to 0.22) and consist of metallic nickel-iron mixed with iron- and magnesium-silicates. They are dominant in the inner main belt within 2.2 AU, common in the central belt within about 3 AU, but become rare further out. The largest is 15 Eunomia (about 330 km wide across its longest dimension), with other large members being 3 Juno and 9 Metis.

Their spectrum has a moderately steep slope at wavelengths shorter than 0.7 μm, and has moderate to weak absorption features around 1 μm and 2 μm. The 1 μm absorption is indicative of the presence of silicates (stony minerals). Often there is also a broad but shallow absorption feature centered near 0.63 μm. The composition of these asteroids is similar to a variety of stony meteorites which share similar spectral characteristics.

S-group asteroids

SMASS classification

In the SMASS classification, several generally "stony" types of asteroids are brought together into a wider S-group which contains the following types:

A-type
K-type
L-type
Q-type
R-type
a core S-type for asteroids having the most "typical" spectra for the S-group
Sa, Sk, Sl, Sq, and Sr-types containing transition objects between the core S-type and the A, K, L, Q, and R-types, respectively.

This whole "S" assemblage of asteroids is spectrally quite distinct from the carbonaceous C-group and the mostly metallic X-group.

Tholen classification

In the Tholen classification the S-type is a very broad grouping which includes all the types in the SMASS S-group except for the A, Q, and R, which have particularly strong "stony" absorption features around 1 μm.

References

S. J. Bus and R. P. Binzel Phase II of the Small Main-belt Asteroid Spectroscopy Survey: A feature-based taxonomy, Icarus, Vol. 158, pp. 146 (2002).

The minor planets
Vulcanoids | Near-Earth asteroids | Main belt | Jupiter Trojans | Centaurs | Damocloids | Comets | Trans-Neptunians (Kuiper belt · Scattered disc · Oort cloud)
For other objects and regions, see: , , asteroid moons and the Solar system
For a complete listing, see: List of asteroids. See also Pronunciation of asteroid names and Meanings of asteroid names.

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