S-type asteroid







433 Eros, an example of an S-type asteroid


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




Contents






  • 1 Characteristics


  • 2 S-group asteroids


    • 2.1 SMASS classification


    • 2.2 Tholen classification


    • 2.3 Stony asteroid families




  • 3 See also


  • 4 References





Characteristics


S-types asteroids, with an astronomical albedo of typically 0.20,[1] 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 is 15 Eunomia (about 330 km wide across its longest dimension), with the next largest members by diameter being 3 Juno, 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.



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 information: Asteroid family § All families

Prominent stony asteroid families with their typical albedo are the:[1]




  • 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





  1. ^ ab "Asteroid Lightcurve Database (README) – 2. Taxonomic Class, orbital class, and albedo". LCDB. Retrieved 16 February 2018..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output .citation q{quotes:"""""""'""'"}.mw-parser-output .citation .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .citation .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Wikisource-logo.svg/12px-Wikisource-logo.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-maint{display:none;color:#33aa33;margin-left:0.3em}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}




  • Bus, S. J.; Binzel, R. P. (2002). "Phase II of the Small Main-belt Asteroid Spectroscopy Survey: A feature-based taxonomy". Icarus. 158 (1): 146–177. Bibcode:2002Icar..158..146B. doi:10.1006/icar.2002.6856.









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