thumb
C-type asteroids are
carbonaceousCarbonaceous is the defining attribute of a substance rich in carbon. Particularly, carbonaceous hydrocarbons are very unsaturated, high-molecular-weight hydrocarbons, having an elevated carbon:hydrogen ratio....
asteroidthumb|260px|right|[[253 Mathilde]], a [[C-type asteroid]] measuring about across. Photograph taken in 1997 by the [[NEAR Shoemaker]] probe.Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, especially in the inner Solar System; they are...
s. They are the most common variety forming around 75% of known
asteroidthumb|260px|right|[[253 Mathilde]], a [[C-type asteroid]] measuring about across. Photograph taken in 1997 by the [[NEAR Shoemaker]] probe.Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, especially in the inner Solar System; they are...
s, and an even higher percentage in the outer part of the belt beyond 2.7
AUAn astronomical unit is a unit of length roughly equal to the mean distance between the Earth and the Sun. It is approximately 150 million kilometres ....
, which is dominated by this asteroid type. The proportion of C-types may actually be greater than this, because C-types are much darker than most other asteroid types except
D-typesD-type asteroids have a very low albedo and a featureless reddish electromagnetic spectrum. It has been suggested that they have a composition of organic rich silicates, carbon and anhydrous silicates, possibly with water ice in their interiors...
and others common only at the extreme outer edge of the Main Belt.
This type of asteroid has very similar spectra to
carbonaceous chondriteCarbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 7 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites...
meteoriteA meteorite is a natural object originating in outer space that survives an impact with the Earth's surface. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s (types CI and CM), whose chemical composition is approximately the same as the
SunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
and the primitive
solar nebulaIn cosmogony, the nebular hypothesis is the most widely accepted model explaining the formation and evolution of the Solar System. It was first proposed in 1734 by Emanuel Swedenborg. Originally applied only to our own Solar System, this method of planetary system formation is now thought to be at...
, except that they do not contain
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
,
heliumHelium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...
and other volatiles.
thumb
C-type asteroids are
carbonaceousCarbonaceous is the defining attribute of a substance rich in carbon. Particularly, carbonaceous hydrocarbons are very unsaturated, high-molecular-weight hydrocarbons, having an elevated carbon:hydrogen ratio....
asteroidthumb|260px|right|[[253 Mathilde]], a [[C-type asteroid]] measuring about across. Photograph taken in 1997 by the [[NEAR Shoemaker]] probe.Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, especially in the inner Solar System; they are...
s. They are the most common variety forming around 75% of known
asteroidthumb|260px|right|[[253 Mathilde]], a [[C-type asteroid]] measuring about across. Photograph taken in 1997 by the [[NEAR Shoemaker]] probe.Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, especially in the inner Solar System; they are...
s, and an even higher percentage in the outer part of the belt beyond 2.7
AUAn astronomical unit is a unit of length roughly equal to the mean distance between the Earth and the Sun. It is approximately 150 million kilometres ....
, which is dominated by this asteroid type. The proportion of C-types may actually be greater than this, because C-types are much darker than most other asteroid types except
D-typesD-type asteroids have a very low albedo and a featureless reddish electromagnetic spectrum. It has been suggested that they have a composition of organic rich silicates, carbon and anhydrous silicates, possibly with water ice in their interiors...
and others common only at the extreme outer edge of the Main Belt.
Characteristics
This type of asteroid has very similar spectra to
carbonaceous chondriteCarbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 7 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites...
meteoriteA meteorite is a natural object originating in outer space that survives an impact with the Earth's surface. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s (types CI and CM), whose chemical composition is approximately the same as the
SunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
and the primitive
solar nebulaIn cosmogony, the nebular hypothesis is the most widely accepted model explaining the formation and evolution of the Solar System. It was first proposed in 1734 by Emanuel Swedenborg. Originally applied only to our own Solar System, this method of planetary system formation is now thought to be at...
, except that they do not contain
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
,
heliumHelium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...
and other volatiles.
HydrateHydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....
d (water-containing) minerals are present.
C-type asteroids are extremely dark with
albedoThe albedo of an object is the extent to which it diffusely reflects light from light sources such as the Sun. It is therefore a more specific form of the term reflectivity. Albedo is defined as the ratio of diffusely reflected to incident electromagnetic radiation. It is a unitless measure...
s typically in the 0.03 to 0.10 range. Consequently, whereas a number of
S-typesS-type asteroids are of a siliceous composition, hence the name. Approximately 17% of asteroids are of this type, making it the second most common after the C-type.-Characteristics:...
can normally be viewed with
binocularsBinoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes with binocular vision when viewing distant objects. Most are sized to be held...
at
oppositionOpposition is a term used in positional astronomy to indicate when one celestial body is on the opposite side of the sky when viewed from a particular place . In particular, two planets are in opposition to each other when their ecliptic longitudes differ by 180°.The symbol of opposition is...
, even the largest C-types require a small
telescopeA telescope is an instrument designed for the observation of remote objects by the collection of electromagnetic radiation. The first known practically functioning telescopes were invented in the Netherlands at the beginning of the 17th century...
. The potentially brightest C-type asteroid is
324 Bamberga324 Bamberga is one of the largest asteroids in the Main asteroid belt. It was discovered by Johann Palisa on February 25, 1892 in Vienna, making it one of the last large asteroids discovered...
, but that object's very high eccentricity means it rarely reaches its maximum
magnitudeThe apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, normalized to the value it would have in the absence of the atmosphere...
.
Their
spectraThe electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
contain moderately strong
ultravioletUltraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than x-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
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 around 3 μm, which can be an indication of water content in minerals is also present.
The largest unequivocally
C-type asteroid is
10 Hygiea10 Hygiea is an asteroid located in the main asteroid belt. With somewhat oblong diameters of 350–500 km, and a mass estimated to be 2.9% of the total mass of the belt, it is the fourth largest object in the region by volume and mass...
, although the SMASS classification places the largest asteroid
1 CeresCeres, formal designation 1 Ceres, is the smallest identified dwarf planet in the Solar System and the only one in the asteroid belt. It was discovered on 1 January 1801, by Giuseppe Piazzi, and is named after the Roman goddess Ceres — the goddess of growing plants, the harvest, and motherly...
, here as well, because that scheme lacks a
G-typeG-type asteroids are a relatively uncommon type of carbonaceous asteroid. The most notable asteroid in this class is 1 Ceres.-Characteristics:Generally similar to the C-type objects, but containing a strong ultraviolet absorption feature below 0.5 μm...
.
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
B-type asteroids are a relatively uncommon type of carbonaceous asteroid, falling into the wider C-group. In the asteroid population, B-class objects are abundant in the outer main belt, and also dominate the high-inclination Pallas family which includes the second-largest asteroid 2 Pallas...
- C-type
- F-type
F-type asteroids are a relatively uncommon type of carbonaceous asteroid, falling into the wider C-group.-Characteristics:Generally similar to the B-type asteroids, but...
- G-type
G-type asteroids are a relatively uncommon type of carbonaceous asteroid. The most notable asteroid in this class is 1 Ceres.-Characteristics:Generally similar to the C-type objects, but containing a strong ultraviolet absorption feature below 0.5 μm...
C-group (SMASS)
In the SMASS classification, the wider C-group contains the types
- B-type
B-type asteroids are a relatively uncommon type of carbonaceous asteroid, falling into the wider C-group. In the asteroid population, B-class objects are abundant in the outer main belt, and also dominate the high-inclination Pallas family which includes the second-largest asteroid 2 Pallas...
corresponding to the Tholen BB-type asteroids are a relatively uncommon type of carbonaceous asteroid, falling into the wider C-group. In the asteroid population, B-class objects are abundant in the outer main belt, and also dominate the high-inclination Pallas family which includes the second-largest asteroid 2 Pallas...
and F-typesF-type asteroids are a relatively uncommon type of carbonaceous asteroid, falling into the wider C-group.-Characteristics:Generally similar to the B-type asteroids, but...
- a core C-type for asteroids having the most "typical" spectra in the group
- Cg and Cgh types corresponding to the Tholen G-type
G-type asteroids are a relatively uncommon type of carbonaceous asteroid. The most notable asteroid in this class is 1 Ceres.-Characteristics:Generally similar to the C-type objects, but containing a strong ultraviolet absorption feature below 0.5 μm...
- Ch type with an absorption feature around 0.7μm
- Cb type corresponding to transition objects between the SMASS C and B types.