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The reflected spectral energy distribution of low-albedo, red-colored, airless bodies in the outer Solar System (planetary satellites, Centaur objects, Kuiper Belt objects, bare comet nuclei) can be modeled with spectral models that incorporate the optical properties of refractory complex organic materials synthesized in the laboratory and called tholins. These materials are strongly colored and impart their color properties to the models. The colors of the bodies cannot be matched with plausible minerals, ices, or metals. Iapetus, a satellite of Saturn, is one such red-colored body that is well matched with tholin-rich models. Detection of aromatic and aliphatic hydrocarbons on Iapetus by the Cassini spacecraft, and the presence of these hydrocarbons in the tholins, is taken as evidence for the widespread presence of solid organic complexes aromatic and aliphatic units on many bodies in the outer Solar System. These organic complexes may be compositionally similar to the insoluble organic matter in some classes of the carbonaceous meteorites, and thus may ultimately derive from the organic matter in the interstellar medium.