Editing Triton (moon) (section)

== Atmosphere ==
{{Main|Atmosphere of Triton|Climate of Triton}}
[[File:The_Horns_of_Triton_-_Voyager_2_(43407605905).png|thumb|left|Departing image of Triton, showing its hazy atmosphere illuminated by sunlight and "extending" its crescent]]

Triton has a tenuous but well-structured and global [[nitrogen]] atmosphere,<ref name="Wind direction"/> with trace amounts of carbon monoxide and small amounts of methane near its surface.<ref name="nature2"/><ref name="grand"/><ref name="Lellouch2010"/> Like [[Pluto]]'s atmosphere, the atmosphere of Triton is thought to result from the evaporation of nitrogen from its surface.<ref name="Cruikshank2004"/> Its surface temperature is at least {{cvt|35.6|K|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.<ref name="Duxburyetal1993"/> An upper limit in the low 40s (K) can be set from vapor pressure equilibrium with nitrogen gas in Triton's atmosphere.<ref name="Tryka1993-Determination"/> This is colder than Pluto's average equilibrium temperature of {{cvt|44|K|C}}. Triton's surface atmospheric pressure is only about {{cvt|1.4–1.9|Pa|mbar|lk=on}}.<ref name="EncycSolSys-Triton"/>
[[File:Tritoncloud.jpg|thumb|Clouds observed above Triton's limb by ''Voyager 2''.]]
Turbulence at Triton's surface creates a [[troposphere]] (a "weather region") rising to an altitude of 8&nbsp;km. Streaks on Triton's surface left by geyser plumes suggest that the troposphere is driven by seasonal winds capable of moving material over a micrometer in size.<ref name="SmithSoderblom1989"/> Unlike other atmospheres, Triton's lacks a [[stratosphere]] and instead has a [[thermosphere]] from altitudes of 8 to 950&nbsp;km and an exosphere above that.<ref name="EncycSolSys-Triton"/> The temperature of Triton's upper atmosphere, at {{val|95|5|u=K}}, is higher than that at its surface, due to heat absorbed from solar radiation and Neptune's [[magnetosphere]].<ref name="nature2"/><ref name="Stevens1992-thermosphere"/> A haze permeates most of Triton's troposphere, thought to be composed largely of [[hydrocarbon]]s and [[nitrile]]s created by the action of sunlight on methane. Triton's atmosphere also has clouds of condensed nitrogen that lie between 1 and 3&nbsp;km from its surface.<ref name="EncycSolSys-Triton"/>

In 1997, observations from [[Earth]] were made of Triton's limb as it [[occultation|passed in front of stars]]. These observations indicated a denser atmosphere than was deduced from ''[[Voyager 2]]'' data.<ref name="Hubblesite"/> Other observations have shown an increase in temperature by 5% from 1989 to 1998.<ref name="MIT Triton"/> These observations indicated Triton was approaching an unusually warm southern hemisphere summer season that happens only once every few hundred years. Hypotheses for this warming include a change of frost patterns on Triton's surface and a change in ice [[albedo]], which would allow more heat to be absorbed.<ref name="Scienceagogo.com"/> Another hypothesis argues that temperature changes are a result of the deposition of dark, red material from geological processes. Because Triton's [[Bond albedo]] is among the highest in the [[Solar System]], it is sensitive to small variations in spectral albedo.<ref name="Nature"/> Based on the increase in atmospheric pressure between 1989 and 1997, it is estimated that by 2010 Triton's atmospheric pressure may have increased to as much as 4 Pa.<ref name="Lellouch2010"/> By 2017, however, Triton's atmospheric surface pressure had nearly returned to ''Voyager 2'' levels; the cause for the rapid spike in atmospheric pressure between 1989 and 2017 remains unexplained.<ref name="Sicardy2024"/>