Editing 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 silicaceous-type) asteroids are [[asteroid]]s with a [[Asteroid spectral type|spectral type]] that is indicative of a [[siliceous]] (i.e. stony) [[mineralogical]] composition, hence the name. They have relatively high density. Approximately 17% of [[Asteroid|asteroids]] are of this type, making it the second-most common after the [[Carbonaceous chondrite|carbonaceous]] [[C-type asteroid|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]]-[[silicate]]s. They are dominant in the [[Kirkwood gap|inner]] part of the [[asteroid belt]] within 2.2 [[astronomical unit|AU]], common in the central belt within about 3 [[astronomical unit|AU]], but become rare farther out. The largest are [[3 Juno]] (about 240&ndash;250&nbsp;km across) and [[15 Eunomia]] (230&nbsp;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 [[micrometre]]s (μm), and has moderate to weak absorption features around 1&nbsp;μm and 2&nbsp;μm. The 1&nbsp;μm absorption is indicative of the presence of [[silicate]]s (stony minerals). Often there is also a broad but shallow absorption feature centered near 0.63&nbsp;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 asteroid|A-type]]
* [[K-type asteroid|K-type]]
* [[L-type asteroid|L-type]]
* [[Q-type asteroid|Q-type]]
* [[R-type asteroid|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-type asteroid#C-group asteroids|C-group]] and the often metallic [[X-type asteroid|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-type asteroid|A]], [[Q-type asteroid|Q]], and [[R-type asteroid|R]], which have particularly strong "stony" absorption features around 1&nbsp;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 ==<!-- end of reflist -->
{{reflist|refs=

<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>

}}
* {{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 (journal)|Icarus]] |volume=158 |issue=1 |pages=146–177 |doi=10.1006/icar.2002.6856 |year=2002 |bibcode=2002Icar..158..146B|s2cid=4880578 }}

{{Asteroids}}
{{Small Solar System bodies}}

[[Category:Asteroid spectral classes]]
[[Category:S-type asteroids|*]]