Triton: Stratospheric molecules and organic sediments

Hydrocarbons and nitriles are produced in Triton's stratosphere by energetic electrons from Neptune's magnetosphere and other charged particle sources. Laboratory plasma experiments reported here show a substantial yield of molecules from low‐pressure flows of 10 −3 CH 4 in N 2 appropriate to Triton if both CH 4 and N 2 are saturated at the surface. An active magnetosphere similar to that of Uranus would result in a flux ∼ 0.3 erg cm −2 s −1 of 0.1–1 MeV electrons in Triton's stratosphere; molecular production rates are then 10 6 ‐10 8 cm −2 s −1 for NH 3 , C 2 H 2 , HCN, and NCCN; tens to hundreds of gm cm −2 of these compounds per 10 9 yr (and lesser quantities of at least eight other molecules experimentally detected) would freeze to fine‐grained white condensates in the lower stratosphere and sediment to the surface. Along with dark/colored organic haze produced in the stratosphere and other heteropolymers produced at the surface, these condensates are subject to redistribution by aeolian processes and may appear as lag deposits and/or sediment layers. A simple eddy diffusion model indicates abundances ∼ 10 19 molec cm −2 for HCN and C 2 H 2 , and > 10 17 molec cm −2 for NCCN, CH 3 CCH, CH 2 CCH 2 , and CH 3 CN in the stratosphere; these and other organic molecules will be detectable by IRIS if the stratosphere is (as expected) heated through ultraviolet and visible light absorption by the haze.