# C-type asteroid
A C-type asteroid is a dark, carbon-rich asteroid whose visible and near-infrared reflectance spectrum resembles that of carbonaceous chondrite meteorites. C-types form the largest spectral class in the asteroid population: NASA's basics-of-space-flight text states that more than 75 percent of asteroids are C-type, dark and reddish with a geometric albedo below 0.10, and a chemical composition similar to the Sun's minus its volatile elements[1](https://science.nasa.gov/learn/basics-of-space-flight/chapter1-3/). A 2018 NASA assessment of the asteroid population gives a lower figure, calling C-types the largest class at 40 percent, so published percentages depend on the survey and weighting used[2](https://ntrs.nasa.gov/api/citations/20180002057/downloads/20180002057.pdf).
| Key fact | Detail |
|---|---|
| Defining properties | Dark and reddish, geometric albedo less than 0.10; spectrum similar to carbonaceous chondrite meteorites[1](https://science.nasa.gov/learn/basics-of-space-flight/chapter1-3/) |
| Composition | Roughly the same chemical composition as the Sun minus its volatiles[1](https://science.nasa.gov/learn/basics-of-space-flight/chapter1-3/) |
| Share of population | More than 75 percent of asteroids per NASA's spaceflight text; a 2018 NASA assessment gives 40 percent as the largest class[1](https://science.nasa.gov/learn/basics-of-space-flight/chapter1-3/) • [2](https://ntrs.nasa.gov/api/citations/20180002057/downloads/20180002057.pdf) |
| Hydration | 60–70% of C-complex asteroids are expected to have hydrated minerals; 77% of C-complex asteroids observed in the AKARI survey show the 2.7 μm water-of-hydration feature[3](https://academic.oup.com/pasj/article/71/1/1/5238131) |
| Meteorite link | Ch-type asteroids correspond closely to CM carbonaceous chondrites, whose spectra mostly show the same 0.7 μm band[4](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JE005584) |
| Sampled members | Ryugu (C-type, 5.4 g returned by Hayabusa2 in 2020) and Bennu (B-type, 121.6 g returned by OSIRIS-REx in 2023)[5](https://www.isas.jaxa.jp/en/topics/004280.html) • [6](https://science.nasa.gov/mission/osiris-rex/) |
| Distribution | The outer main belt, centered near 3.2 au, is rich in carbon-bearing asteroids, while the inner belt near 2.8 au is silicate-rich[1](https://science.nasa.gov/learn/basics-of-space-flight/chapter1-3/) |
## Taxonomy
Asteroid spectral classes arose from cluster analysis of colors, albedos, and spectra. In the Tholen (1984) taxonomy, built from Eight-Color Asteroid Survey photometry, 190 asteroids were classified as type C, the largest single class in that survey[7](https://www.sciencedirect.com/science/article/pii/0019103578900854). Later systems split the low-albedo population further. In the Bus-DeMeo taxonomy the C-complex includes B, C, Cg, Ch, and related subtypes, and a 2022 taxonomy that reintroduces visual albedo places the P-class within the C-complex[8](https://arxiv.org/abs/2203.11229).
The suffix "h" marks hydration. C-complex asteroids showing an absorption feature in the broad 0.7 μm band are categorized as Ch- or Cgh-type, and the band arises from an Fe²⁺–Fe³⁺ charge-transfer transition in oxidized iron in phyllosilicates formed by aqueous alteration, the reaction of anhydrous rock with liquid water inside a parent body[3](https://academic.oup.com/pasj/article/71/1/1/5238131). The 0.7 μm band is the defining characteristic of the Ch class in the Bus-DeMeo system, so every Ch and Cgh asteroid can be assumed to carry hydrated minerals[4](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JE005584).
## Hydration signatures
Water of hydration in C-type surfaces is read from two absorptions. The 2.7 μm band, attributed to the OH-stretch in hydrated minerals, is the more direct indicator of water; the 0.7 μm band is an indirect signifier that has only been seen on asteroids and in meteorites together with a 3 μm band[3](https://academic.oup.com/pasj/article/71/1/1/5238131) • [4](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JE005584). Early 3 μm spectrophotometry found water-of-hydration features in 9 C-class asteroids, with band intensities from 6 to 23 percent[9](https://www.sciencedirect.com/science/article/pii/0019103585900028).
**How common is hydration?** Rivkin (2012) reported that 60–70 percent of C-complex asteroids are expected to have hydrated minerals, and the AKARI near-infrared survey found the 2.7 μm feature in 77 percent of the C-complex asteroids it observed, though the authors note possible observational bias[3](https://academic.oup.com/pasj/article/71/1/1/5238131). The two bands do not always appear together: if the 0.7 μm band is present, the 2.7 μm feature always accompanies it, but a 2.7 μm band can occur without the 0.7 μm band, and some objects show neither[3](https://academic.oup.com/pasj/article/71/1/1/5238131).
A few large outer-belt members carry surface ice instead. Rivkin and Emery (2010) matched the spectrum of 24 Themis with a model of ice-coated pyroxene grains and amorphous carbon, suggesting very fine water frost as grain coatings[3](https://academic.oup.com/pasj/article/71/1/1/5238131). Such Themis-like 3 μm band shapes have not been identified among near-Earth objects, whose surfaces are too hot for near-surface ice[4](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JE005584).
## Distribution in the Solar System
C-type asteroids dominate the outer main belt. Data from the [Sloan Digital Sky Survey](https://www.edgepedia.org/sloan-digital-sky-survey) divide the belt into an inner belt centered at 2.8 au, containing silicate-rich asteroids, and an outer belt centered at 3.2 au, containing asteroids rich in carbon[1](https://science.nasa.gov/learn/basics-of-space-flight/chapter1-3/). The largest body of the class is the dwarf planet 1 [Ceres](https://www.edgepedia.org/ceres-dwarf-planet), classified as a C-type asteroid, about 940 km across and holding 35 percent of the main belt's total mass[10](https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1945-5100.2003.tb00321.x) • [11](https://science.nasa.gov/mission/dawn/science/ceres/).
Among near-Earth asteroids the class is rarer. In a 2016 study, Carry et al. identified 54 near-Earth asteroids whose Sloan colors matched C-type taxonomy, plus 4 that showed B-type colors; separately, the Binzel et al. (2004) spectroscopic survey turned up 13 C-type and 5 B-type bodies.[4](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JE005584)
## Link to carbonaceous chondrites
Most main-belt C-type asteroids have spectra similar to carbonaceous type 1 and 2 (CI and CM) meteoritic materials, although a significant minority show a different, opaque-rich mafic silicate assemblage[12](https://ntrs.nasa.gov/api/citations/19790024054/downloads/19790024054.pdf). The closest match is between the Ch asteroids and the CM chondrites: the vast majority of CM meteorite spectra show the 0.7 μm band, which is rare or absent in other meteorite groups, and 3 μm band shapes and albedo are consistent between the Ch asteroids and CM material[4](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JE005584). Experiments in the laboratory back up the view, broadly held among meteorite researchers, that CM, CI, and CR carbonaceous chondrites coming from asteroids of the C-complex underwent aqueous alteration within the bodies they came from.[3](https://academic.oup.com/pasj/article/71/1/1/5238131)
## Sampled C-type asteroids
Three missions have returned asteroid samples to Earth: JAXA's Hayabusa and [Hayabusa2](https://www.edgepedia.org/hayabusa2) and NASA's OSIRIS-REx[5](https://www.isas.jaxa.jp/en/topics/004280.html). Hayabusa2 collected samples from the C-type asteroid [162173 Ryugu](https://www.edgepedia.org/162173-ryugu) between 2018 and 2019 and delivered them to Earth on December 5, 2020, returning two samples of 5.4 grams each[13](https://www.space.com/astronomy/asteroids/ryugu-asteroid-sample-contains-all-five-key-components-of-dna-scientists-find). The Ryugu particles have a bulk density of 1,282 ± 231 kg/m³, more porous than known primitive chondrites, and such high-microporosity material has not been found in any meteorite recovered on Earth, probably because it is too fragile to survive atmospheric entry[14](https://www.nature.com/articles/s41550-021-01550-6).
OSIRIS-REx returned 121.6 grams (4.29 ounces) of material from 101955 Bennu in September 2023, the largest asteroid sample ever collected in space[6](https://science.nasa.gov/mission/osiris-rex/). Bennu is classified as a B-type, a class with strong observational similarities to C-types such as Ryugu, and the two agencies exchanged samples for the first comparative analysis of two pristine carbonaceous asteroids[5](https://www.isas.jaxa.jp/en/topics/004280.html).
**Organic content.** The returned samples show that carbonaceous asteroid bodies hosted liquid water and complex chemistry. [Ryugu samples](https://www.edgepedia.org/ryugu-samples) contain the nucleobases adenine, guanine, cytosine, thymine, and uracil, the building blocks of DNA and RNA[13](https://www.space.com/astronomy/asteroids/ryugu-asteroid-sample-contains-all-five-key-components-of-dna-scientists-find). Samples from Bennu include a minimum of 14 of the 20 amino acids that Earth life employs, plus 19 additional amino acids that biology does not use, together with sodium-bearing minerals thought to be leftovers of salty waters on an ancient water world[15](https://www.space.com/astronomy/asteroids/asteroid-bennu-samples-nasa-transported-to-earth-reveal-lifes-building-blocks-could-be-pretty-widespread) • [16](https://apnews.com/article/e3318592d16a53bea56c1ff689555f0d). One Ryugu grain analyzed by NASA carried 3.76 ± 0.14 wt.% total carbon and 1.14 ± 0.09 wt.% total hydrogen[17](https://ntrs.nasa.gov/api/citations/20230002235/downloads/Dworkin.soluble.updated%202023.03.16.pdf).
## References
1. [Chapter 1: The Solar System, NASA Science – Basics of Space Flight](https://science.nasa.gov/learn/basics-of-space-flight/chapter1-3/)
2. [Asteroid Threat Assessment, NASA NTRS (2018)](https://ntrs.nasa.gov/api/citations/20180002057/downloads/20180002057.pdf)
3. [AKARI/IRC near-infrared asteroid spectroscopic survey: AcuA-spec, Publications of the Astronomical Society of Japan](https://academic.oup.com/pasj/article/71/1/1/5238131)
4. [How Many Hydrated NEOs Are There? Rivkin, Journal of Geophysical Research: Planets (2019)](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JE005584)
5. [The science from asteroid sample return missions, ISAS/JAXA](https://www.isas.jaxa.jp/en/topics/004280.html)
6. [NASA's OSIRIS-REx Mission to Asteroid Bennu, NASA Science](https://science.nasa.gov/mission/osiris-rex/)
7. [Taxonomy of asteroids, Tholen (1984), Icarus](https://www.sciencedirect.com/science/article/pii/0019103578900854)
8. [Asteroid Taxonomy from Cluster Analysis of Spectrometry and Albedo, arXiv:2203.11229](https://arxiv.org/abs/2203.11229)
9. [The nature of C-class asteroids from 3-μm spectrophotometry, Icarus](https://www.sciencedirect.com/science/article/pii/0019103585900028)
10. [Hydrogen concentrations on C-class asteroids derived from remote sensing, Meteoritics & Planetary Science](https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1945-5100.2003.tb00321.x)
11. [Ceres, NASA Science – Dawn mission](https://science.nasa.gov/mission/dawn/science/ceres/)
12. [Asteroid and meteorite spectra, NASA NTRS (1979)](https://ntrs.nasa.gov/api/citations/19790024054/downloads/19790024054.pdf)
13. [Ryugu asteroid sample contains all five key components of DNA, Space.com](https://www.space.com/astronomy/asteroids/ryugu-asteroid-sample-contains-all-five-key-components-of-dna-scientists-find)
14. [Preliminary analysis of the Hayabusa2 samples returned from C-type asteroid Ryugu, Nature Astronomy](https://www.nature.com/articles/s41550-021-01550-6)
15. [Asteroid samples NASA brought to Earth suggest life's building blocks may be widespread, Space.com](https://www.space.com/astronomy/asteroids/asteroid-bennu-samples-nasa-transported-to-earth-reveal-lifes-building-blocks-could-be-pretty-widespread)
16. [NASA's asteroid samples hold salty remains of ancient water world, AP News](https://apnews.com/article/e3318592d16a53bea56c1ff689555f0d)
17. [Soluble organic compounds in Ryugu sample A0106, NASA NTRS](https://ntrs.nasa.gov/api/citations/20230002235/downloads/Dworkin.soluble.updated%202023.03.16.pdf)
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*Topic: Encyclopedia › Physical world and mathematics › Astronomy › Solar System › Solar System bodies › Asteroid spectral and compositional types*
*Initially written Sep 17, 2026 · Reviewed: Sep 19, 2026; Oct 15, 2026 · Edited: Sep 19, 2026; Oct 11, 2026; Oct 15, 2026 · Last review: Oct 15, 2026*
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