 | This articleneeds additional citations forverification. Please helpimprove this article byadding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "C-type asteroid" – news ·newspapers ·books ·scholar ·JSTOR(June 2010) (Learn how and when to remove this message) |
_mathilde.jpg)
C-type (carbonaceous/ˌkɑːrbəˈneɪʃəs/)asteroids are the most common variety, forming around 75% of knownasteroids.[1] They are volatile-rich and distinguished by a very lowalbedo because their composition includes a large amount ofcarbon, in addition to rocks and minerals. They have an average density of about1.7 g/cm3.
They lie most often at the outer edge of theasteroid belt, 3.5 au (520 million km; 330 million mi) from theSun, where 80% of the asteroids are of this type[2], whereas only 40% of asteroids at 2 au (300 million km; 190 million mi) from the Sun are C-type.[3] The proportion of C-types may actually be greater than this, since C-types are much darker (and henceless detectable) than most other asteroid types, except forD-types and others that lie mostly at the extreme outer edge of the asteroid belt.
Asteroids of this class havespectra very similar to those ofcarbonaceous chondritemeteorites (types CI and CM). The latter are very close in chemical composition to theSun and the primitivesolar nebula minushydrogen,helium and other volatiles.Hydrated (water-containing) minerals are present.[4]
C-type asteroids are extremely dark, withalbedos typically in the 0.03 to 0.10 range. Consequently, whereas a number ofS-type asteroids can normally be viewed withbinoculars atopposition, even the largest C-type asteroids require a smalltelescope. The potentially brightest C-type asteroid is324 Bamberga, but that object's very higheccentricity means it rarely reaches its maximummagnitude.
Theirspectra contain moderately strongultraviolet 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 of1.7 g/cm3.[5]
The largest unequivocally C-type asteroid is10 Hygiea, although theSMASS classification places the largest asteroid,1 Ceres, here as well, because that scheme lacks aG-type.
In theTholen classification, the C-type is grouped along with three less numerous types into a wider C-group of carbonaceous asteroids which contains:[citation needed]
In theSMASS classification, the wider C-group contains the types:[citation needed]
| Main | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Distribution |
| ||||||||
| Classification |
| ||||||||
| Exploration | |||||||||
| Lists | |||||||||
| Related | |||||||||
