[Previous] | [Session 69] | [Next]
J. I. Moses (LPI)
Exogenic material from comets, interplanetary dust particles (IDPs), or satellites and rings can have conspicuous effects on the chemistry and physics of outer-planetary atmospheres. Comets such as Shoemaker-Levy 9 occasionally deposit large amounts of vaporized and solid debris in giant-planet atmospheres. The vapor initiates interesting oxygen, nitrogen, and sulfur chemistry in the stratosphere, while the solid debris causes localized heating and can affect atmospheric dynamics. Strong shocks created during the bolide and plume-splashback phases of the cometary impacts profoundly affect the thermal structure and chemistry of localized areas. IDPs that ablate high in the planet's atmosphere will also affect atmospheric thermal structure and chemistry, but less sporadically and more globally than comets. For example, the ablated meteoritic material can affect ionospheric structure and chemistry --- metal ions can replace hydrocarbon ions as the dominant species in the lower ionosphere (facilitating the formation of layered structures), and recondensed refractory material can affect the structure and diurnal variability of the lower ionosphere. The meteoritic material also introduces oxygen compounds and instigates neutral oxygen photochemistry in the stratosphere. Water from meteoritic sources can condense in outer-planetary stratospheres, contributing to the global haze layers, and refractory meteoritic material can condense high in the atmosphere, leading to upper-atmospheric heating and providing surfaces upon which other molecules can condense or upon which heterogeneous chemical reactions can occur. Material from the planet's rings and/or satellites can affect the atmosphere in some of the same ways as IDPs; moreover, ring material can affect chemistry and structure in the topside ionosphere, and heavy ions from satellites such as Io can cause auroral heating and chemistry. The evidence for extraplanetary material in the atmospheres of giant planets will be reviewed.