Geysers near Triton's South Pole spew dark material high into the moon's atmosphere. As this plume settles back down to Triton's surface, it appears to indicate prevailing winds moving from lower-left towards upper-right in this image.
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Image courtesy NASA/JPL/USGS.
The Atmosphere of Triton
Triton, by far the largest moon of Neptune, is slightly smaller than Earth's Moon. Triton has the coldest surface temperatures in our Solar System. Surprisingly, this frigid moon has an atmosphere, albeit a very thin one. Atmospheric pressure on Earth is at least 50,000 times higher than on the surface of Triton!
Another surprise... nitrogen is the main gas in Triton's atmosphere, just as it is on Earth! Triton is so cold that most of its nitrogen is on the moon's surface as frost. Some of that frost has evaporated, however, creating Triton's atmosphere. Triton also has numerous ice geysers that spew nitrogen, dust, and/or methane compounds up to 8 km (5 miles) high into the atmosphere. Scientists have detected clouds of nitrogen ice particles between 1 and 3 km (3 to 10 thousand feet) above the surface as well as a haze layer made of hydrocarbons which forms when sunlight strikes methane molecules in Triton's air. Streaks of dark deposits appear to form downwind of geysers, apparently showing the direction of seasonal prevailing winds near Triton's South Pole.
Like Earth's atmosphere, Triton's atmosphere has layers. Turbulence near the moon's surface creates a troposphere ("weather region") that rises to an altitude of 8 km (5 miles). Triton's atmosphere lacks a stratosphere, but it does have a thermosphere and an exosphere. The upper atmosphere extends to 800 or more km (500+ miles) above Triton's surface.
Triton's atmosphere seems to be warming slightly. Although it is still extremely cold, it appears that the temperature rose 5% in about a decade. Some scientists think Triton is approaching an unusually warm summer that only happens once every few hundred years.
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