S-type asteroid

{{short description|Asteroid spectral type indicating stony composition}} [[File:Eros - PIA02923 (color).jpg|thumb|433 Eros, an example of an S-type asteroid]]

'''S-type''' (stony-type or siliceous-type) asteroids are asteroids with a spectral type that is indicative of a siliceous (i.e. stony) mineralogical composition, hence the name. They have relatively high density. Approximately 17% of asteroids are of this type, making it the second-most common after the carbonaceous C-type.

== Characteristics == S-type asteroids, with an astronomical albedo of typically 0.20,<ref name="LCDB-albedos" /> are moderately bright and consist mainly of iron- and magnesium-silicates. They are dominant in the inner part of the asteroid belt within 2.2 AU, common in the central belt within about 3 AU, but become rare farther out. The largest are 3 Juno (about 240–250 km across) and 15 Eunomia (230 km), with other large S-types being 29 Amphitrite, 532 Herculina and 7 Iris. These largest S-types are visible in 10x50 binoculars at most oppositions; the brightest, 7 Iris, can occasionally become brighter than +7.0, which is a higher magnitude than any asteroid except the unusually reflective 4 Vesta.

Their spectrum has a moderately steep slope at wavelengths shorter than 0.7 micrometres (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.

Due to their volatile-poor (rocky) composition, S-type asteroids have relatively high density. A survey of 11 S-type asteroids found an average density of {{val|3.0|u=g/cm3}}.<ref name=VLT>P. Vernazza et al. (2021) VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis. ''Astronomy & Astrophysics'' 54, A56 </ref>

== 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. The entire "S"-assemblage of asteroids is spectrally quite distinct from the carbonaceous C-group and the often 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.

=== Stony asteroid families === {{Further|Asteroid family#All families}}

Prominent stony asteroid families with their typical albedo are the:<ref name="LCDB-albedos" /> * Eos family (0.14) * Eunomia family (0.21) * Flora family (0.24) * Koronis family (0.24) * Nysa family (0.20) * Phocaea family (0.23)

== See also == * Asteroid spectral types * X-type asteroid

== References == <references> <ref name="LCDB-albedos">{{cite web |title = Asteroid Lightcurve Database (README) – 2. Taxonomic Class, orbital class, and albedo |publisher = LCDB |url = http://www.minorplanet.info/datazips/LCDB_readme.txt |access-date = 16 February 2018 |archive-date = 16 November 2015 |archive-url = https://web.archive.org/web/20151116190637/http://www.minorplanet.info/datazips/LCDB_readme.txt |url-status = dead }}</ref> </references> * {{cite journal |ref=Bus2002 |first1=S. J. |last1=Bus |first2=R. P. |last2=Binzel |title=Phase II of the Small Main-belt Asteroid Spectroscopy Survey: A feature-based taxonomy |journal=Icarus |volume=158 |issue=1 |pages=146–177 |doi=10.1006/icar.2002.6856 |year=2002 |bibcode=2002Icar..158..146B|s2cid=4880578 }}

Category:Asteroid spectral classes *