Models of organic-rich surfaces in the outer solar system.

摘要

This thesis applies light-scattering theory along with recently-measured optical constants of astronomically-interesting organic materials in an attempt to understand the surfaces of representative organic-rich bodies in the outer Solar System.; The Centaur 5145 Pholus has a visible and near-ir spectrum redder than any other object in the Solar System. Its color can be reproduced by an intraparticle mixture of water ice, Titan tholin, and either astronomical silicate or polymerized hydrogen cyanide. The solar UV flux, combined with surface gardening by micrometeoroids, will convert all carbon-bearing ices to dark organic solids in the top millimeter of Kuiper Belt Objects in {dollar}{lcub}sim{rcub}10sp7{dollar} yrs. Initially red, further irradiation makes the surface more neutral. If impacts expose fresh ice over a large fraction of the object's surface on a similar time scale, an average red color may be retained. The color diversity observed in the Centaur and Kuiper Belt populations thus can be explained by a variation in the average exposure ages of their surfaces.; The dark material on the leading hemisphere of Iapetus has a spectrum that is too generic, lacking in absorption features, to strongly constrain models of its composition; many mixtures of water ice, organics, and/or silicates can reproduce its albedo and spectrum. Several mechanisms have been proposed to explain why one hemisphere of Iapetus is extremely dark while the other hemisphere is very bright, but this thesis finds major flaws in most of them. A scheme postulating a global, several-km-thick layer of dark material covered by a layer of ice {dollar}sim{dollar}1-m thick, but which is excavated on the leading hemisphere, works best.; Finally, the impacts of the fragments of Comet Shoemaker-Levy 9 into Jupiter left behind dark atmospheric blemishes that may be composed of organic matter. The optical constants of the blemish aerosols--as derived by others--are near-perfect matches to Murchison organic residue. The reflectances of the initial impact plumes and the thermal pulse during plume collapse are inconsistent with the blemish aerosols, so the organic matter had to have formed in situ, rather than being cometary debris.