Climate of Triton

Background

Triton's atmosphere is composed mainly of nitrogen, with minor methane and carbon monoxide. Its surface pressure is heavily variable, rising from 1.4 Pa at the Voyager 2 flyby to roughly 4 Pa by 2010, then dropping back to 1.454 Pa by 2022. Surface temperatures measured by Voyager 2 ranged from 34 to 44 K, with an extrapolated value of 37.5 K, consistent with nitrogen's vapor pressure. By 1997, the surface temperature had increased to 39.3 K.

Triton's atmosphere hosts a distinct troposphere, possibly defined thermally or by wind shear. Winds are inferred from dark streaks on the southern polar cap and from two active plumes, Hili and Mahilani, whose columns streak westward at about 8 km altitude, possibly marking the tropopause. Early wind speed estimates near the south pole were 5–15 m/s, but later modeling suggested weaker westerly winds below 0.5 m/s. Global circulation models during southern summer show a general south-to-north flow, with retrograde winds up to 10 m/s above the equator.

Clouds observed by Voyager 2 are thin, bright, likely composed of condensed nitrogen crystals, with an optical depth of about 0.063 in violet light. Up to one-third of Triton's southern limb was covered by clouds. Atmospheric haze, similar to that on Pluto and Titan, extends up to ~30 km, formed by ultraviolet light acting on methane and nitrogen, producing tholin particles 100–200 nm in size. Triton's haze differs from Pluto's due to its colder lower atmosphere and differences in methane abundance.

Did You Know?

• Triton's atmosphere is about as hazy as the Martian atmosphere when no dust storms are in progress.