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J. A. Stansberry (Lowell Observatory)
Recent stellar occultation observations of Triton's atmosphere (Elliot et al., Nature, 1998) indicate that the atmospheric pressure has doubled since the 1989 Voyager II encounter. If one accepts that the bright material seen on Triton by Voyager consists of volatile frost deposits, the distribution of those frosts is puzzling in light of simple energy balance and seasonal transport models. A change of perspective may help solve this puzzle in light of the Elliot et al. observations of seasonal pressure change. Rather than starting from the premise that the distribution of the volatile ices controls the atmospheric pressure, it is just as valid to assume that the atmospheric pressure controls what portions of the surface will be covered in volatile ices. If Triton's atmospheric pressure were increasing in 1989, as it seems to have been since 1989, the northern margin of South Polar Cap could well have been migrating towards the equator, rather than receding from it as is predicted by most seasonal transport models. If this was the case, we are left with a new puzzle which is, what is driving the seasonal pressure increase?