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Triton’s Changing Atmosphere

Presentation #323.06 in the session Uranus and Neptune Systems (Poster)

Published onOct 23, 2023
Triton’s Changing Atmosphere

Throughout the entire period Triton’s atmosphere has been measured, from Voyager 2 in 1989 through the most recent stellar occultation measurements, Triton has been in a southern summer orientation. Its pole position has slowly evolved from a maximum sub-solar latitude of approximately –50 degrees in the late 1990’s through to –35 degrees today, as it moves towards the summer-ending Triton equinox in the late 2040’s (Park et al. 2021 AJ 161).

Given the decades-long southern summer, one might expect the constant insolation of the southern hemispheric ice formations to result in increasing atmospheric pressure during this period. In fact, rapid growth was observed during the peak portion of the southern summer as occultation observations from 1995 through 2001 showed atmospheric pressure increasing two-fold in just those seven years. (Elliot et al. 1998 Nature 393; Person et al. 2001 BAAS 33)

This trend was seen to suddenly reverse in 2017, with an occultation showing the pressure retreating towards its earlier levels, losing about half of the previously observed increases. (Person et al. 2018 DPS 50; this work) Unfortunately, the lack of suitable candidates prevented significant Triton observations in the period between 2002 and 2017, with only a few detections of low signal-to-noise ratio over those 15 years.

That the observed rapid growth of the late 1990’s has not only slowed with the ebbing summer, but apparently reversed in the course of just a few years indicates that Triton’s atmospheric response to insolation is much less straight forward than simple polar cap warming models might suggest. Differences in thermal inertia between ice layers and different material transport models may help to explain some of this reaction (Hansen and Paige 1992 Icarus 99; Spencer and Moore 1992 Icarus 99; Bertrand et al., 2019 DPS 51, etc.), but as yet the sudden reversal remains unconstrained by modelling efforts.

Here we present the analysis of the October 2022 Triton occultation of a 11.5 Gaia G magnitude star, which was extensively observed throughout Asia and environs by numerous groups. We present this reduction along with a re-reduction of prior occultation events with the same software and models in an attempt to verify the puzzling trends in Triton’s atmosphere and provide a reliable and consistent atmospheric baseline for the development of newer models.

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