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G-type asteroids are a relatively uncommon type of carbonaceous asteroid that makes up approximately 5% of asteroids. The most notable asteroid in this class is 1 Ceres.
Carbon is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Three isotopes occur naturally, 12C and 13C being stable, while 14C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity.
Asteroids are minor planets, especially of the inner Solar System. Larger asteroids have also been called planetoids. These terms have historically been applied to any astronomical object orbiting the Sun that did not resemble a planet-like disc and was not observed to have characteristics of an active comet such as a tail. As minor planets in the outer Solar System were discovered they were typically found to have volatile-rich surfaces similar to comets. As a result, they were often distinguished from objects found in the main asteroid belt. In this article, the term "asteroid" refers to the minor planets of the inner Solar System including those co-orbital with Jupiter.
Generally similar to the C-type objects, but contain a strong ultraviolet absorption feature below 0.5 μm. An absorption feature around 0.7 μm may also be present, which is indicative of phyllosilicate minerals such as clays or mica.
Ultraviolet (UV) designates a band of the electromagnetic spectrum with wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation is present in sunlight, and contributes about 10% of the total light output of the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules.
Clay is a finely-grained natural rock or soil material that combines one or more clay minerals with possible traces of quartz (SiO2), metal oxides (Al2O3, MgO etc.) and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure. Clays are plastic due to particle size and geometry as well as water content, and become hard, brittle and non–plastic upon drying or firing. Depending on the soil's content in which it is found, clay can appear in various colours from white to dull grey or brown to deep orange-red.
The mica group of sheet silicate (phyllosilicate) minerals includes several closely related materials having nearly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition. The nearly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms.
In the SMASS classification the G-type corresponds to the Cgh and Cg types, depending on the presence or absence (respectively) of the absorption feature at 0.7 μm. The G-type, C-type and some rare types are sometimes collected together into a wider C-group of carbonaceous asteroids.
C-type (carbonaceous) asteroids are the most common variety, forming around 75% of known asteroids. They are distinguished by a very low albedo because their composition includes a large amount of carbon, in addition to rocks and minerals. They occur most frequently at the outer edge of the asteroid belt, 3.5 astronomical units (AU) from the Sun, where 80% of the asteroids are of this type, whereas only 40% of asteroids at 2 AU from the Sun are C-type. The proportion of C-types may actually be greater than this, because C-types are much darker than most other asteroid types except for D-types and others that are mostly at the extreme outer edge of the asteroid belt.
A V-type asteroid or Vestoid is an asteroid whose spectral type is that of 4 Vesta. Approximately 6% of main-belt asteroids are vestoids, with Vesta being by far the largest of them. They are relatively bright, and rather similar to the more common S-type asteroid, which are also made up of stony irons and ordinary chondrites, with V-types containing more pyroxene than S-types.
S-type asteroids are asteroids with a spectral type that is indicative of a siliceous mineralogical composition, hence the name. Approximately 17% of asteroids are of this type, making it the second most common after the carbonaceous C-type.
M-type asteroids are asteroids of partially known composition; they are moderately bright. Some, but not all, are made of nickel–iron, either pure or mixed with small amounts of stone. These are thought to be pieces of the metallic core of differentiated asteroids that were fragmented by impacts, and are thought to be the source of iron meteorites. M-type asteroids are the third most common asteroid type.
Chondrites are stony (non-metallic) meteorites that have not been modified due to melting or differentiation of the parent body. They are formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids. They are the most common type of meteorite that falls to Earth with estimates for the proportion of the total fall that they represent varying between 85.7% and 86.2%. Their study provides important clues for understanding the origin and age of the Solar System, the synthesis of organic compounds, the origin of life and the presence of water on Earth. One of their characteristics is the presence of chondrules, which are round grains formed by distinct minerals, that normally constitute between 20% and 80% of a chondrite by volume.
T-type asteroids are rare inner-belt asteroids of unknown composition with dark, featureless and moderately red spectra, and a moderate absorption feature shortwards of 0.85 µm. No direct meteorite analog has been found to date. Thought to be anhydrous, they are considered to be related to P-types or D-types, or possibly a highly altered C-type. One example is 114 Kassandra.
Q-type asteroids are relatively uncommon inner-belt asteroids with a strong, broad 1 micrometre olivine and pyroxene feature, and a spectral slope that indicates the presence of metal. There are absorption features shortwards and longwards of 0.7 µm, and the spectrum is generally intermediate between the V and S-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 can be found in the outer asteroid belt, and also dominate the high-inclination Pallas family which includes the second-largest asteroid 2 Pallas. They are thought to be primitive, volatile-rich remnants from the early Solar System. There are 65 known B-type asteroids in the SMASS classification, and 9 in the Tholen classification as of March 2015.
F-type asteroids are a relatively uncommon type of carbonaceous asteroid, falling into the wider C-group.
Lutetia is a large asteroid in the asteroid belt of an unusual spectral type. It measures about 100 kilometers in diameter. It was discovered in 1852 by Hermann Goldschmidt, and is named after Lutetia, the Latin name of Paris.
2934 Aristophanes, provisional designation 4006 P-L, is a carbonaceous Veritasian asteroid from the outer regions of the asteroid belt, approximately 22 kilometers in diameter. It was discovered during the Palomar–Leiden survey in 1960, and later named after ancient Greek dramatist Aristophanes.
Aglaja is a large, dark main belt asteroid. It was discovered by Robert Luther on 15 September 1857 from Düsseldorf. The name was chosen by the Philosophical Faculty of the University of Bonn and refers to Aglaea, one of the Charites in Greek mythology.
Klymene is a large, dark Themistian asteroid that was discovered by J. C. Watson on September 13, 1868, and named after one of the many Clymenes in Greek mythology. It is classified as a C-type asteroid, indicating it probably has a carbonaceous composition. The spectra indicates the presence of aqueous-altered minerals on the surface based upon a sharp feature at a wavelength of 3 μm, and, as of 2015, is the only member of the Themis family found to show this absorption.
Siwa is a large and dark main-belt asteroid that was discovered by Austrian astronomer Johann Palisa on October 13, 1874, and named after Šiwa, the Slavic goddess of fertility.
K-type asteroids are relatively uncommon asteroids with a moderately reddish spectrum shortwards of 0.75 μm, and a slight bluish trend longwards of this. They have a low albedo. Their spectrum resembles that of CV and CO meteorites.
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 surface and internal compositions are presumably similar, while large bodies such as Ceres and Vesta are known to have internal structure. Over the years, there has been a number of surveys that resulted in a set of different taxonomic systems such as the Tholen, SMASS and Bus–DeMeo classification.
The X-group of asteroids collects together several types with similar spectra, but probably quite different compositions.
The rare O-type asteroids have spectra similar to the unusual asteroid 3628 Boznemcová, which is the best asteroid match to the spectra of L6 and LL6 ordinary chondrite meteorites. Their spectra have a deep absorption feature longward of 0.75 μm.
2099 Öpik, provisional designation 1977 VB, is a dark and eccentric asteroid and Mars-crosser from the inner regions of the asteroid belt, approximately 5.1 kilometers in diameter.
16560 Daitor, provisional designation 1991 VZ5, is a larger Jupiter trojan from the Trojan camp, approximately 44 kilometers (27 miles) in diameter. It was discovered on 2 November 1991, by Belgian astronomer Eric Elst at the La Silla site of the European Southern Observatory in Chile. The carbonaceous C-type asteroid is one of the largest Jupiter trojans with an unknown rotation period. It was named after the Trojan warrior Daitor from Greek mythology.
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