S-type asteroids are asteroids with a

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

that is indicative of a

siliceous Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

(i.e. stony)

mineralogical Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the p ...

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, are moderately bright and consist mainly of iron- and

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

- silicates. They are dominant in the

inner Interior may refer to: Arts and media * ''Interior'' (Degas) (also known as ''The Rape''), painting by Edgar Degas * ''Interior'' (play), 1895 play by Belgian playwright Maurice Maeterlinck * ''The Interior'' (novel), by Lisa See * Interior de ...

part of the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, c ...

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 532 Herculina is a large asteroid, with a diameter of around 200 km. Discovery It was discovered on April 20, 1904, by Max Wolf in Heidelberg, and initially catalogued as 1904 NY. The origin of its name is not known; it may be named afte ...

and

7 Iris Iris (minor planet designation: 7 Iris) is a large main-belt asteroid and perhaps remnant planetesimal orbiting the Sun between Mars and Jupiter. It is the fourth-brightest object in the asteroid belt. It is classified as an S-type asteroid, mea ...

. 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 The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

s (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 .P. Vernazza et al. (2021) VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis. ''Astronomy & Astrophysics'' 54, A56

S-group asteroids

SMASS classification

In the

SMASS classification An asteroid spectral type is assigned to asteroids based on their emission spectrum, color, and sometimes albedo. These types are thought to correspond to an asteroid's surface composition. For small bodies that are not internally differentiat ...

, 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 is a horizontally scrolling shooter arcade video game developed and released by Irem in 1987 and the first game in the ''R-Type'' series. The player controls a star ship, the R-9 "Arrowhead", in its efforts to destroy the Bydo, a powerful ...

* 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 The C-Group culture is an archaeological culture found in Lower Nubia, which dates from ca. 2400 BCE to ca. 1550 BCE. It was named by George A. Reisner. With no central site and no written evidence about what these people called themselves, Re ...

and the often metallic

X-group The X-Group Culture was an ancient civilization that existed from ca. 300 CE to ca. 600 CE. It was centered in Nubia stretching from the Dodekaschoinos in the north to Delgo in the south. George A. Reisner coined the term ''X-Group Culture'' for ...

Tholen classification

In the

Tholen classification An asteroid spectral type is assigned to asteroids based on their emission spectrum, color, and sometimes albedo. These types are thought to correspond to an asteroid's surface composition. For small bodies that are not internally differentiated ...

, 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

Prominent stony

asteroid families An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic o ...

with their typical albedo are the: *

Eos family The Eos family (''adj. Eoan'' ; ) is a very large asteroid family located in the outer region of the asteroid belt. The family of K-type asteroids is believed to have formed as a result of an ancient catastrophic collision. The family's parent body ...

(0.14) *

Eunomia family The Eunomia or Eunomian family () is a large asteroid family of S-type asteroids named after the asteroid 15 Eunomia. It is the most prominent family in the intermediate asteroid belt and the 6th-largest family with nearly six thousand known member ...

(0.21) *

Flora family The Flora family (''adj. Florian''; ; also known as ''Ariadne family'') is a prominent family of stony asteroids located in the inner region of the asteroid belt. It is one of the largest families with more than 13,000 known members, or approxi ...

(0.24) * Koronis family (0.24) *

Nysa family The Nysa family (adj. ''Nysian''; FIN: 405) is part of the Nysa–Polana complex, the largest cluster of asteroid families in the asteroid belt. It is located in the inner region of the asteroid belt, orbiting the Sun between 2.41 and 2.5 A ...

(0.20) * Phocaea family (0.23)

References