Detection of CO in Triton's atmosphere and the nature of surface-atmosphere interactions

TL;DR

This study reports the first infrared detection of gaseous CO and methane in Triton's atmosphere, revealing seasonal variability and surface-atmosphere interactions affecting its composition and temperature.

Contribution

It provides the first infrared spectroscopic detection of CO and methane in Triton's atmosphere, offering new insights into surface-atmosphere interactions and seasonal changes.

Findings

First infrared detection of gaseous CO in Triton.

Methane partial pressure is higher than previous ultraviolet estimates.

Atmospheric CO is linked to surface CO-enriched veneer.

Abstract

Triton possesses a thin atmosphere, primarily composed of nitrogen, sustained by the sublimation of surface ices. The goal is to determine the composition of Triton's atmosphere and to constrain the nature of surface-atmosphere interactions. We perform high-resolution spectroscopic observations in the 2.32-2.37 $\mu$m range, using CRIRES at the VLT. From this first spectroscopic detection of Triton's atmosphere in the infrared, we report (i) the first observation of gaseous methane since its discovery in the ultraviolet by Voyager in 1989 and (ii) the first ever detection of gaseous CO in the satellite. The CO atmospheric abundance is remarkably similar to its surface abundance, and appears to be controlled by a thin, CO-enriched, surface veneer resulting from seasonal transport and/or atmospheric escape. The CH$_4$ partial pressure is several times larger than inferred from Voyager. This confirms that Triton's atmosphere is seasonally variable and is best interpreted by the warming of CH$_4$-rich icy grains as Triton passed southern summer solstice in 2000. The presence of CO in Triton's atmosphere also affects its temperature, photochemistry and ionospheric composition. An improved upper limit on CO in Pluto's atmosphere is also reported.