Atmosphere of Triton - Structure

Structure

Triton's atmosphere is well structured and global. The atmosphere extends up to 800 kilometers above the surface, where the exobase is located, and had a surface pressure of about 14 microbars as of 1989. This is only 1/70,000th of the surface pressure on Earth. The surface temperature was at least 35.6 K (−237.6 °C) because Triton's nitrogen ice is in the warmer, hexagonal crystalline state, and the phase transition between hexagonal and cubic nitrogen ice occurs at that temperature. An upper limit in the low 40s (K) can be set from vapor pressure equilibrium with nitrogen gas in Triton's atmosphere. The most likely temperature was 38 ± 1 K as of 1989. Later in 1990s it probably increased by about 1 K owing to the general global warming on Triton (see below).

Convection near Triton's surface heated by the Sun creates a troposphere (a "weather region") rising to an altitude of about 8 km. In it temperature decreases with height reaching a minimum of about 36 K at the tropopause. There is no stratosphere, defined as a layer where heating from the warmer troposphere and thermosphere is balanced by radiative cooling. Higher regions include the thermosphere (8–850 km) and exosphere (above 850 km). In the thermosphere the temperature rises reaching a constant value of about 95 kelvins above 300 km. The upper atmosphere continuously leaks into the space due to the weak gravity of Triton. The loss rate is about 1×1025 nitrogen molecules per second, which equals about 0.3 kg/s.