Global mineralogical mapping of Mars by the Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activité (OMEGA) instrument on the European Space Agency's Mars Express spacecraft provides new information on Mars' geological and climatic history. Phyllosilicates formed by aqueous alteration very early in the planet's history (the “phyllocian” era) are found in the oldest terrains; sulfates were formed in a second era (the “theiikian” era) in an acidic environment. Beginning about 3.5 billion years ago, the last era (the “siderikian”) is dominated by the formation of anhydrous ferric oxides in a slow superficial weathering, without liquid water playing a major role across the planet.

[1] We have developed a one-dimensional, diurnally averaged, photochemical model for Jupiter's stratosphere that couples photodissociation, chemical kinetics, vertical diffusion, and radiative transport. The predictions regarding the abundances and vertical profiles of hydrocarbon compounds are compared with observations from the Infrared Space Observatory (ISO) to better constrain the atmospheric composition, to better define the eddy diffusion coefficient profile, and to better understand the chemical reaction schemes that produce and destroy the observed constituents. From model-data comparisons we determine that the C 2 H 6 mole fraction on Jupiter is (4.0 ± 1.0) Â 10 À6 at 3.5 mbar and (2.7 ± 0.7) Â 10 À6 at 7 mbar, and the C 2 H 2 mole fraction is (1.4 ± 0.8) Â 10 À6 at 0.25 mbar and (1.5 ± 0.4) Â 10 À7 at 2 mbar. The column densities of CH 3 C 2 H and C 6 H 6 are (1.5 ± 0.4) Â 10 15 cm À2 and (8.0 ± 2) Â 10 14 cm À2 , respectively, above 30 mbar. Using identical reaction lists, we also have developed photochemical models for Saturn, Uranus, and Neptune. Although the models provide good first-order predictions of hydrocarbon abundances on the giant planets, our current chemical reaction schemes do not reproduce the relative abundances of C 2 H x hydrocarbons. Unsaturated hydrocarbons like C 2 H 4 and C 2 H 2 appear to be converted to saturated hydrocarbons like C 2 H 6 more effectively on Jupiter than on the other giant planets, more effectively than is predicted by the models. Further progress in our understanding of photochemistry at low temperatures and low pressures in hydrogen-dominated atmospheres hinges on the acquisition of high-quality kinetics data.