1. Max-Planck-lnstitut für Aeronomie, D-3411 Katlenburg-Lmdau, FRG

Abstract

SATURN'S planet-sized moon Titan has a nitrogen-rich atmosphere with a surface pressure of 1.6 bar (ref. 1). Methane, ethylene and other hydrocarbons are also present, allowing photochemical synthesis of complex organic molecules and aerosols^2–6. The ablation of meteoroids in Titan's upper atmosphere could contribute to the atmospheric chemistry in two important respects. First, refractory elements such as sodium, iron and magnesium could recondense into small (10–100 Å) particles which could act as aerosol nucleation centres, as in the Earth's atmosphere^7,8. Second, meteoroids from stray bodies with perihelia of 3 AU could be rich in volatile ices (H₂O, CO₂, CO), and might constitute an important source of oxygen-bearing material in Titan's atmosphere. Here I use a simple model of meteoroid ablation to calculate the altitude profiles of material introduced in this way from both icy and rocky meteoroids. The source region of oxygen-bearing molecules is found to lie between 600 and 800 km altitude ; on Earth, by comparison, most of the meteoritic material evaporates between 80 and 100 km (refs 9,10).