C-type asteroid

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253 Mathilde, a C-type asteroid (253) mathilde.jpg
253 Mathilde, a C-type asteroid

C-type (carbonaceous) asteroids are the most common variety, forming around 75% of known asteroids. [1] They are volatile-rich and distinguished by a very low albedo because their composition includes a large amount of carbon, in addition to rocks and minerals. Their density averages at about 1.7 g/cm3. 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. [2] The proportion of C-types may actually be greater than this, because C-types are much darker (and therefore less detectable) than most other asteroid types except for D-types and others that are mostly at the extreme outer edge of the asteroid belt.

Contents

Characteristics

Asteroids of this class have spectra very similar to those of carbonaceous chondrite meteorites (types CI and CM). The latter are very close in chemical composition to the Sun and the primitive solar nebula minus hydrogen, helium and other volatiles. Hydrated (water-containing) minerals are present. [3]

C-type asteroids are extremely dark, with albedos typically in the 0.03 to 0.10 range. Consequently, whereas a number of S-type asteroids can normally be viewed with binoculars at opposition, even the largest C-type asteroids require a small telescope. The potentially brightest C-type asteroid is 324 Bamberga, but that object's very high eccentricity means it rarely reaches its maximum magnitude.

Their spectra contain moderately strong ultraviolet 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 1.7 g/cm3. [4]

The largest unequivocally C-type asteroid is 10 Hygiea, although the SMASS classification places the largest asteroid, 1 Ceres, 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:[ citation needed ]

C-group (SMASS)

In the SMASS classification, the wider C-group contains the types:[ citation needed ]

See also

Related Research Articles

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 asteroid Asteroid spectral type indicating stony composition

S-type asteroids are asteroids with a spectral type that is indicative of a siliceous mineralogical 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.

M-type asteroid Asteroid spectral 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.

P-type asteroids are asteroids that have low albedo and a featureless reddish spectrum. It has been suggested that they have a composition of organic rich silicates, carbon and anhydrous silicates, possibly with water ice in their interior. P-type asteroids are found in the outer asteroid belt and beyond. There are in the neighborhood of 33 known P-type asteroids, depending on the classification, including 46 Hestia, 65 Cybele, 76 Freia, 87 Sylvia, 153 Hilda, 476 Hedwig and, in some classifications, 107 Camilla.

G-type asteroid

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.

B-type asteroid Asteroid spectral class; uncommon type of carbonaceous asteroid

B-type asteroids are a relatively uncommon type of carbonaceous asteroid, falling into the wider C-group; the 'B' indicates these objects are spectrally blue. 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.

21 Lutetia Main-belt asteroid

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.

47 Aglaja

47 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. It was rendered Aglaia in English sources into the early 20th century, as 'i' and 'j' are equivalent in Latin names and in the Latin rendering of Greek names.

92 Undina

Undina, minor planet designation 92 Undina, is a large main belt asteroid. The asteroid was discovered by Christian Peters on 7 July 1867 from the Hamilton College Observatory. It is named for the eponymous heroine of Undine, a popular novella by Friedrich de la Motte Fouqué.

Aletheia is a very large main-belt asteroid that was discovered by German–American astronomer Christian Peters on June 28, 1886, at Litchfield Observatory, Clinton, New York. The dark and heterogeneously composed X-type asteroid contains primitive carbonaceous materials, responsible for its low albedo of 0.04. Aletheia measures about 185 kilometers in diameter and belongs to the largest asteroids of the main-belt. It has a semi-major axis of 3.1 AU and an orbit inclined by 11 degrees with a period of 5.55 years.

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.

L-type asteroids are relatively uncommon asteroids with a strongly reddish spectrum shortwards of 0.75 μm, and a featureless flat spectrum longwards of this. In comparison with the K-type, they exhibit a more reddish spectrum at visible wavelengths and a flat spectrum in the infrared.

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.

735 Marghanna is a large carbonaceous background asteroid from the central regions of the asteroid belt, approximately 74 kilometers in diameter. It was discovered on 9 December 1912, by German astronomer Heinrich Vogt at the Heidelberg-Königstuhl State Observatory in southwest Germany. The dark C-type asteroid (Ch) has a rotation period of 20.6 hours and is rather regular in shape. It was named after Margarete Vogt and after Hanna, the mother and a relative of the discoverer, respectively.

776 Berbericia

776 Berbericia is a minor planet orbiting the Sun. A main-belt C-type asteroid, it was discovered on 24 January 1914 by astronomer Adam Massinger at Heidelberg Observatory in southwest Germany. It was named by Max Wolf in honor of Adolf Berberich (1861–1920), a German astronomer. The spectra of the asteroid displays evidence of aqueous alteration.

Space weathering

Space weathering is the type of weathering that occurs to any object exposed to the harsh environment of outer space. Bodies without atmospheres take on many weathering processes:

1155 Aënna, provisional designation 1928 BD, is an asteroid from the inner regions of the asteroid belt, approximately 11 kilometers in diameter. It was discovered on 26 January 1928, by German astronomer Karl Reinmuth at Heidelberg Observatory in southwest Germany. It is named for the astronomy journal Astronomische Nachrichten.

Asteroidal water is water or water precursor deposits such as hydroxide (OH) that exist in asteroids. The "snow line" of the Solar System lies outside of the main asteroid belt, and the majority of water is expected in minor planets (e.g., Kuiper belt objects and Centaurs. Nevertheless, a significant amount of water is also found inside the snow line, including in near-earth objects.

References

  1. Gradie et al. pp. 316-335 in Asteroids II. edited by Richard P. Binzel, Tom Gehrels, and Mildred Shapley Matthews, Eds. University of Arizona Press, Tucson, 1989, ISBN   0-8165-1123-3
  2. "Asteroids: Structure and composition of asteroids". ESA.
  3. Norton, O. Richard (2002). The Cambridge Encyclopedia of Meteorites. Cambridge: Cambridge University Press. pp. 121–124. ISBN   0-521-62143-7.
  4. P. Vernazza et al. (2021) VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis. Astronomy & Astrophysics 54, A56