Discovery of carbon monoxide in the upper atmosphere of Pluto

TL;DR

This paper reports the first detection of gaseous carbon monoxide in Pluto's upper atmosphere, revealing significant atmospheric changes over a decade likely due to increased surface-ice evaporation or pressure expansion.

Contribution

It provides the first observational evidence of CO in Pluto's upper atmosphere and shows that Pluto's atmospheric composition and structure have changed markedly since 2000.

Findings

Detection of gaseous CO via 1.3mm wavelength transition.

The CO line brightness is more than twice previous tentative results.

The CO molecules extend up to approximately 3 Pluto radii above the surface.

Abstract

Pluto's icy surface has changed colour and its atmosphere has swelled since its last closest approach to the Sun in 1989. The thin atmosphere is produced by evaporating ices, and so can also change rapidly, and in particular carbon monoxide should be present as an active thermostat. Here we report the discovery of gaseous CO via the 1.3mm wavelength J=2-1 rotational transition, and find that the line-centre signal is more than twice as bright as a tentative result obtained by Bockelee-Morvan et al. in 2000. Greater surface-ice evaporation over the last decade could explain this, or increased pressure could have caused the atmosphere to expand. The gas must be cold, with a narrow line-width consistent with temperatures around 50 K, as predicted for the very high atmosphere, and the line brightness implies that CO molecules extend up to approximately 3 Pluto radii above the surface. The upper atmosphere must have changed markedly over only a decade since the prior search, and more alterations could occur by the arrival of the New Horizons mission in 2015.