C-type (

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

aceous ) asteroids are the most common variety, forming around 75% of known

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

s. They are volatile-rich and distinguished by a very low

albedo Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...

because their composition includes a large amount of

, in addition to rocks and minerals. They have an average density of about . They lie most often at the outer edge of the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...

, from the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

, where 80% of the asteroids are of this type, whereas only 40% of asteroids at from the Sun are C-type. The proportion of C-types may actually be greater than this, since C-types are much darker (and hence less detectable) than most other asteroid types, except for D-types and others that lie mostly at the extreme outer edge of the asteroid belt.

Characteristics

Asteroids of this class have spectra very similar to those of carbonaceous chondrite

meteorite A meteorite is a rock (geology), rock that originated in outer space and has fallen to the surface of a planet or Natural satellite, moon. When the original object enters the atmosphere, various factors such as friction, pressure, and chemical ...

s (types CI and CM). The latter are very close in chemical composition to the

and the primitive

solar nebula There is evidence that the formation of the Solar System began about 4.6 bya, billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, whil ...

minus

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

and other volatiles.

Hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

d (water-containing) minerals are present. C-type asteroids are extremely dark, with

s typically in the 0.03 to 0.10 range. Consequently, whereas a number of S-type asteroids can normally be viewed with

binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...

at opposition, even the largest C-type asteroids require a small

telescope A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...

. The potentially brightest C-type asteroid is 324 Bamberga, but that object's very high

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

means it rarely reaches its maximum

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

. Their spectra contain moderately strong

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

absorption at wavelengths below about 0.4 μm to 0.5 μm, while at longer wavelengths they are largely featureless but slightly reddish. The so-called "water" absorption feature of around 3 μm, which can be an indication of water content in minerals, is also present. Due to their volatile-rich (icy) composition, C-type asteroids have relatively low density. A survey of 20 C-type asteroids found an average density of . The largest unequivocally C-type asteroid is 10 Hygiea, although the SMASS classification places the largest asteroid,

1 Ceres Ceres ( minor-planet designation: 1 Ceres) is a dwarf planet in the middle main asteroid belt between the orbits of Mars and Jupiter. It was the first known asteroid, discovered on 1 January 1801 by Giuseppe Piazzi at Palermo Astronomical O ...

, here as well, because that scheme lacks a G-type.

C-group classifications

C-group (Tholen)

In the Tholen classification, the C-type is grouped along with three less numerous types into a wider C-group of carbonaceous asteroids which contains: * B-type * C-type * F-type * G-type

C-group (SMASS)

In the SMASS classification, the wider C-group contains the types: * B-type corresponding to the Tholen B and F-types * a core C-type for asteroids having the most "typical" spectra in the group * Cg and Cgh types corresponding to the Tholen G-type * Ch type with an absorption feature around 0.7μm * Cb type corresponding to transition objects between the SMASS C and B types

References

{{DEFAULTSORT:C-Type Asteroid Asteroid spectral classes * *

Characteristics

C-group classifications

C-group (Tholen)

C-group (SMASS)

See also

References