C-type asteroids are the most common type of asteroids, forming around 75% of all known asteroids in the solar system.
Key Facts & Summary
- C-type asteroids are among the darkest celestial objects in color.
- They are the most numerous asteroids in the Solar System.
- Though Ceres is classified as a G-type asteroid, it falls under the C-type group; thus, the dwarf-asteroid-planet is the most massive asteroid of the C-class type.
- C-type asteroids are among the most ancient celestial objects in our solar system.
- They have a charcoal-like appearance due to their high concentration of carbon.
- C-type asteroids share the same spectral classification as carbonaceous meteorites.
- The C-type asteroids have albedos typically in the 0.03 and 0.10 range.
- The total mass of all known asteroids constitutes around 4% of the Moon’s mass.
- Most asteroids have irregular shapes similar to that of a potato.
- Though they are among the most numerous, their low albedo makes them very difficult to observe.
- Most C-type asteroids are located in the famous asteroid belt.
- The average distance between asteroids is around 600.000 mi / 1 million km.
- One day, the entire asteroid belt will be gone. This will happen when the Sun approaches the end of its life.
- The C-type asteroid group holds together three other sub-groups of carbonaceous asteroids: B-type, F-type, and G-type.
Around 80% of the asteroids located there are of this kind, whereas 40% of asteroids at 2 AU from the Sun are C-type. Their proportions may be even higher than this. Since C-type asteroids are usually dark, much darker than other types of asteroids, except for D-types, they are also less detectable.
All asteroids are rocky remnants from 4.6 billion years ago. They are leftovers from the early solar system. Most of them are located in the central asteroid belt between Mars and Jupiter. The thickness of the asteroid belt is believed to be at around 1 AU.
They orbit the Sun, and among them, the C-type asteroids are the most ancient. In the asteroid belt, there are several groups of different estimated ages. The Karin family, for example, is believed to have formed around 5.7 million years ago out of a single object. The Veritas family around 8.3 million years ago, and the Datura family at only 53.000 years ago.
The C-type asteroids consist of clay, minerals, and silicate rocks, and are dark in appearance. They are carbonaceous – a large amount of carbon – and since they are far away from the Sun, they have been the least altered by heat, this also testifies their old age.
Since most haven’t reached temperatures above 50 degrees Celsius, it is believed that they contain at least around 22% water. Their albedo is very low, precisely because they have high amounts of carbon in their composition.
C-type asteroids have a spectral class similar to those of carbonaceous chondrite meteorites- type CI and CM – the latter is very close in chemical composition to the Sun, and even the primitive solar nebula, without the hydrogen, helium, and other volatiles.
There are though hydrated – water-containing – minerals. The C-type asteroids have albedos typically in the 0.03 and 0.10 range. Even the largest C-type asteroids require a small telescope to be viewed, whereas S-type asteroids, for example, can be observed with binoculars.
The brightest C-type asteroid to be found, 324 Bamberga, is an exception. Though, its high eccentric orbit rarely helps it reach its maximum magnitude.
The spectra of C-type asteroids contain moderately strong ultraviolet absorption at wavelengths below 0.4 um to 0.5 um. At longer wavelengths, they are mainly featureless but slightly reddish.
The water absorption feature of around 3 um in C-type asteroids, is an indication of water content in minerals.
Size & Mass
The largest unequivocally C-type asteroid is 10 Hygiea, having a diameter of 434 km / 270 mi. However, the SMASS classification places the largest asteroid, 1 Ceres, here as well since Ceres is a G-type asteroid part of the larger C-type group.
The C-type asteroids come in different sizes. They range from 0.5 mi to 587 mi / 1 km to 945 km in diameter. The total mass of all known asteroids constitutes around 4% of the Moon’s mass.
Some C-type asteroids are merely piles of rubble held together by gravity. Most of them aren’t massive enough, and as such, their shape is irregular, sometimes resembling that of a potato.
The Tholen classification system places the C-type asteroid group along with three less numerous types of carbonaceous asteroids such as:
B-type – a relatively uncommon type of carbonaceous asteroid of which the second-largest asteroid, 2 Pallas, is also part of. It Has a diameter of 510 km / 320 mi.
F-type – another peculiar model of carbonaceous asteroids falling into the full C-type group.
G-type – They represent around 5% of all asteroids. The most notable is Ceres, the largest asteroid known. It has a diameter of 945 km / 587 mi.
Millions of asteroids more than 0.5 mi / 1 km across are in the asteroid belt. However, there are even smaller ones and they dominate in terms of numbers.
The average distance between asteroids is around 600.000 mi / 1 million km. A spacecraft can safely travel there and explore, many SCI-FI movies often exaggerate the closeness of asteroids.
Though C-type asteroids are the most numerous and have survived for millions of years, one day, the entire asteroid belt will be gone. This will happen when the Sun approaches the end of its life. The Sun’s powerful last light will shatter the asteroids with radiation.
Did you know?
- The initial C for C-type stands for carbon.
- If you stood on an asteroid in the asteroid belt, you wouldn’t be able to see the other asteroids due to their size and overall distance.
- The meteorites found on Earth are thought to be pieces of C-type asteroids that suffered collisions and broke off of the larger body.
- Some believe that the asteroid belt is merely the remnants of a destroyed planet. However, the calculated remaining mass is not enough to support this.