GLOBAL warming on Neptune鈥檚 icy moon Triton has taken astronomers by
surprise.
Triton presents different faces to the Sun depending on Neptune鈥檚 position in
its orbit, and it is now nearing the point where the Sun is highest over the
moon鈥檚 south pole. Astronomers had expected this to cause nitrogen-rich polar
ices to evaporate.
Last November a team led by Jim Elliot of the Massachusetts Institute of
Technology used the Hubble Space Telescope to monitor changes in light from a
distant star as Triton passed in front of it. The results showed that Triton鈥檚
atmosphere is warming faster than anyone predicted. 鈥淲e were expecting a
seasonal cycle, but we weren鈥檛 sure what that cycle would be,鈥� says team member
Steve McDonald.
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The team says in this week鈥檚 Nature (vol 393, p 765) that temperatures 48
kilometres above the surface increased from 47 kelvin in 1995 to 50.3 kelvin
last year. They say the atmosphere appears to have doubled in volume over the
past 10 years as surface ices evaporated.