Observations made during the New Horizons flyby provide a detailed snapshot of the current state of Pluto's atmosphere. While the lower atmosphere (at altitudes <200 km) is consistent with ground-based stellar occultations, the upper atmosphere is much colder and more compact than indicated by pre-encounter models. Molecular nitrogen (N2) dominates the atmosphere (at altitudes <1800 km or so), while methane (CH4), acetylene (C2H2), ethylene (C2H4), and ethane (C2H6) are abundant minor species, and likely feed the production of an extensive haze which encompasses Pluto. The cold upper atmosphere shuts off the anticipated enhanced-Jeans, hydrodynamic-like escape of Pluto's atmosphere to space. It is unclear whether the current state of Pluto's atmosphere is representative of its average state--over seasonal or geologic time scales.
@article{arxiv.1604.05356,
title = {The Atmosphere of Pluto as Observed by New Horizons},
author = {G. Randall Gladstone and S. Alan Stern and Kimberly Ennico and Catherine B. Olkin and Harold A. Weaver and Leslie A. Young and Michael E. Summers and Darrell F. Strobel and David P. Hinson and Joshua A. Kammer and Alex H. Parker and Andrew J. Steffl and Ivan R. Linscott and Joel Wm. Parker and Andrew F. Cheng and David C. Slater and Maarten H. Versteeg and Thomas K. Greathouse and Kurt D. Retherford and Henry Throop and Nathaniel J. Cunningham and William W. Woods and Kelsi N. Singer and Constantine C. C. Tsang and Rebecca Schindhelm and Carey M. Lisse and Michael L. Wong and Yuk L. Yung and Xun Zhu and Werner Curdt and Panayotis Lavvas and Eliot F. Young and G. Leonard Tyler and the New Horizons Science Team},
journal= {arXiv preprint arXiv:1604.05356},
year = {2021}
}