D-type asteroids have a very low albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

 and a featureless reddish electromagnetic spectrum

Electromagnetic spectrum

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....

. It has been suggested that they have a composition of organic rich silicate

Silicate

A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...

s, carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 and anhydrous

Anhydrous

As a general term, a substance is said to be anhydrous if it contains no water. The way of achieving the anhydrous form differs from one substance to another...

 silicates, possibly with water ice

Ice

Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

 in their interiors. D-type asteroids are found in the outer asteroid belt

Asteroid belt

The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...

 and beyond; examples are 152 Atala

152 Atala

152 Atala is a very large, dark main belt asteroid. It is a type D asteroid, meaning that it is composed of carbon, organic rich silicates and possibly water ice...

, 588 Achilles

588 Achilles

588 Achilles is an asteroid discovered on February 22, 1906, by the German astronomer Max Wolf. It was the first of the trojan asteroids to be discovered, and is named after Achilles, the fictional hero from the Iliad. It orbits in the Lagrangian point of the Sun-Jupiter system...

, 624 Hektor

624 Hektor

624 Hektor is the largest Jupiter Trojan. It was discovered in 1907 by August Kopff.Hektor is a D-type asteroid, dark and reddish in colour. It lies in Jupiter's leading Lagrangian point, , called the 'Greek' node after one of the two sides in the legendary Trojan War...

 and 944 Hidalgo

944 Hidalgo

944 Hidalgo is a small Solar System body with a semi-major axis beyond Jupiter's and an orbital period of 13.77 years. This makes it a centaur, but it was discovered in 1920 and has hence traditionally been considered an asteroid....

.

The Nice model

Nice model

The Nice model is a scenario for the dynamical evolution of the Solar System. It is named for the location of the Observatoire de la Côte d'Azur, where it was initially developed, in Nice, France. It proposes the migration of the giant planets from an initial compact configuration into their...

 suggests that D-type asteroids may be captured Kuiper belt objects.

In 1992, Larry A. Lebofsky and colleagues published an article in which they detected a spectral feature at 3 micrometre

Micrometre

A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...

s in 773 Irmintraud

773 Irmintraud

773 Irmintraud is a minor planet that orbits the Sun between the planets Mars and Jupiter. Discovered by German astronomer Franz Kaiser at Heidelberg, Germany, on December 22, 1913, the planetoid was named for Irmtraud, an old German woman's name that appears frequently in old songs and sagas. This...

, a main-belt D-type asteroid. This feature was believed to indicate the presence of water on the surface and to indicate that the D-type asteroid was more likely to be in an altered state rather than in an unaltered, primitive or primordial state.