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A stellar occultation by Neptune's main satellite, Triton, was observed on 5October 2017 from Europe, North Africa, and the USA. We derived 90 light curvesfrom this event, 42 of which yielded a central flash detection.  We aimed at constraining Triton's atmospheric structure and the seasonalvariations of its atmospheric pressure since the Voyager 2 epoch (1989). Wealso derived the shape of the lower atmosphere from central flash analysis. Weused Abel inversions and direct ray-tracing code to provide the density,pressure, and temperature profiles in the altitude range $\sim$8 km to$\sim$190 km, corresponding to pressure levels from 9 {\mu}bar down to a fewnanobars.  Results. (i) A pressure of 1.18$\pm$0.03 {\mu}bar is found at a referenceradius of 1400 km (47 km altitude). (ii) A new analysis of the Voyager 2 radioscience occultation shows that this is consistent with an extrapolation ofpressure down to the surface pressure obtained in 1989. (iii) A survey ofoccultations obtained between 1989 and 2017 suggests that an enhancement insurface pressure as reported during the 1990s might be real, but debatable, dueto very few high S/N light curves and data accessible for reanalysis. Thevolatile transport model analysed supports a moderate increase in surfacepressure, with a maximum value around 2005-2015 no higher than 23 {\mu}bar. Thepressures observed in 1995-1997 and 2017 appear mutually inconsistent with thevolatile transport model presented here. (iv) The central flash structure doesnot show evidence of an atmospheric distortion. We find an upper limit of0.0011 for the apparent oblateness of the atmosphere near the 8 km altitude.

Constraints on the structure and seasonal variations of Triton's atmosphere from the 5 October 2017 stellar occultation and previous observations