Complex Organic Solid Matter in the Outer Solar System

Abstract

Complex organic molecular material of non-biological origin is found in abundance in the interstellar dust in our Galaxy, and is also detected in other galaxies. Some of this material was incorporated into the solar nebula and is now found in some Solar System bodies. While some pre-solar organic material has been preserved, synthesis of complex organics in planetary atmospheres and on icy surfaces has been in progress for the entire age of the Solar System. Refractory organic solids have proven difficult to detect by traditional spectroscopic techniques, and their presence is usually inferred from the low albedo and (often) red color of the surfaces of small bodies in the outer Solar System (OSS). Color in complex organic molecules, such as polymers and polycyclic aromatic hydrocarbons, is caused by absorption in the UV and visible spectral regions arising from electronic transitions connected primarily with C-C and C-0 bonding. In particular, large hydrocarbon molecules with conjugated (alternating pairs of double and single) C-C bonds have color because the electronic transitions of the de-localized pi electrons extend into the visible spectral region; the longer the conjugated chain, the further is the extension to longer wavelength, with the result that especially large molecular material appears black.