1. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA

Abstract

THE recent Voyager encounter established certain facts about Triton's atmosphere: the surface pressure is in the range 1.5–1.9 Pa (15–19 bar)¹; the surface temperature is 383K (ref. 2); molecular nitrogen is the dominant atmospheric constituent³; hazes and clouds are visible not only on the limb but also against the surface⁴; the wind in the southern hemisphere is to the northeast at low altitudes (as shown by streaks on the surface⁴) and to the west at high altitudes (as shown by geyser-like plume tails⁴). Triton rotates with a period of 5.877 days in a right-hand sense about the south pole, where the season now is late spring⁴. Here we argue that these features can be explained if Triton, like Mars⁵, has a global, well-structured atmosphere in equilibrium with surface frosts. The subliming frost cap produces a polar anticyclone at low altitudes, with northeastward winds of 5 m s^-1 within the Ekman boundary layer. The temperature contrast between the cold frost-covered pole and the warm unfrosted equator produces westward winds at high altitudes.