Triton, Neptune's largest moon, has been predicted to undergo significant seasonal changes that would reveal themselves as changes in its mean frost temperature1,2,3. But whether this temperature should at the present time be increasing, decreasing or constant depends on a number of parameters (such as the thermal properties of the surface, and frost migration patterns) that are unknown. Here we report observations of a recent stellar occultation by Triton which, when combined with earlier results, show that Triton has undergone a period of global warming since 1989. Our most conservative estimates of the rate of temperature and surface-pressure increase during this period imply that the atmosphere is doubling in bulk every 10 years—significantly faster than predicted by any published frost model for Triton2,3. Our result suggests that permanent polar caps on Triton play a dominant role in regulating seasonal atmospheric changes. Similar processes should also be active on Pluto.
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We thank E. Nelan and B. McArthur for help in reducing our data; the IRTF staff, the staff of the Lear Jet Observatory at NASA Ames, F. Osell, M. Kakkala, J. Kern, R. Meserole, C. Dahn and R. Stone for assistance; and D. Strobel for discussions. This work was supported, in part, by NASA, NSF, and the National Geographic Society. The NASA/ESA Hubble Space Telescope observations were supported by STScI, which is operated by Association of Universities for Research in Astronomy, Incorporated.
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Elliot, J., Hammel, H., Wasserman, L. et al. Global warming on Triton. Nature 393, 765–767 (1998). https://doi.org/10.1038/31651
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