Journal Article

The atmosphere of Pluto as observed by New Horizons

Tyler, G. Leonard, Curdt, Werner, Strobel, Darrell F., Yung, Yuk L., Young, Eliot F., Olkin, Catherine B., Retherford, Kurt D., Kammer, Joshua A., Weaver, Harold A., Summers, Michael E., Throop, Henry, Singer, Kelsi N., Lisse, Carey M., Ennico, Kimberly, Woods, William W., Slater, David C., Zhu, Xun, Gladstone, G. Randall, Wong, Michael L., Hinson, David P., Steffl, Andrew J., Versteeg, Maarten H., Cunningham, Nathaniel J., Parker, Alex H., Greathouse, Thomas K., Lavvas, Panayotis, Linscott, Ivan R., Stern, S. Alan, Young, Leslie A., Parker, Joel Wm, Cheng, Andrew F., Schindhelm, Eric, Tsang, Constantine C. C.

2016

Overview

In July 2015, the New Horizons spacecraft flew through the Pluto system at high speed, humanity's first close look at this enigmatic system on the outskirts of our solar system. In a series of papers, the New Horizons team present their analysis of the encounter data downloaded so far: Moore et al. present the complex surface features and geology of Pluto and its large moon Charon, including evidence of tectonics, glacial flow, and possible cryovolcanoes. Grundy et al. analyzed the colors and chemical compositions of their surfaces, with ices of H 2 O, CH 4 , CO, N 2 , and NH 3 and a reddish material which may be tholins. Gladstone et al. investigated the atmosphere of Pluto, which is colder and more compact than expected and hosts numerous extensive layers of haze. Weaver et al. examined the small moons Styx, Nix, Kerberos, and Hydra, which are irregularly shaped, fast-rotating, and have bright surfaces. Bagenal et al. report how Pluto modifies its space environment, including interactions with the solar wind and a lack of dust in the system. Together, these findings massively increase our understanding of the bodies in the outer solar system. They will underpin the analysis of New Horizons data, which will continue for years to come. Science , this issue pp. 1284 , 10.1126/science.aad9189 , 10.1126/science.aad8866 , 10.1126/science.aae0030 , & 10.1126/science.aad9045 Pluto’s atmosphere is cold, rarefied, and made mostly of nitrogen and methane, with layers of haze. Observations made during the New Horizons flyby provide a detailed snapshot of the current state of Pluto’s atmosphere. Whereas the lower atmosphere (at altitudes of less than 200 kilometers) is consistent with ground-based stellar occultations, the upper atmosphere is much colder and more compact than indicated by pre-encounter models. Molecular nitrogen (N 2 ) dominates the atmosphere (at altitudes of less than 1800 kilometers or so), whereas methane (CH 4 ), acetylene (C 2 H 2 ), ethylene (C 2 H 4 ), and ethane (C 2 H 6 ) are abundant minor species and likely feed the production of an extensive haze that 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.

• Publisher: American Association for the Advancement of Science,The American Association for the Advancement of Science
• Subject: Astronomy / Atmosphere / Boundary layers / Chemical reactions / Ethane / Haze / Low temperature / Methane / Nitrogen / Opacity / Orography / Photochemicals / Pluto / RESEARCH ARTICLE SUMMARY / Space telescopes / Spacecraft / Sublimation / Temperature inversions / Upper atmosphere