Editing Pluto (section)

== Atmosphere ==
{{Main|Atmosphere of Pluto}}
[[File:PIA21590 – Blue Rays, New Horizons' High-Res Farewell to Pluto.jpg|thumb|upright=1.28|A near-true-color image taken by ''New Horizons'' after its flyby. Numerous layers of blue haze float in Pluto's atmosphere. Along and near the limb, mountains and their shadows are visible.]]Pluto has a tenuous [[atmosphere]] consisting of [[nitrogen]] (N<sub>2</sub>), [[methane]] (CH<sub>4</sub>), and carbon monoxide (CO), which are in [[equilibrium vapor pressure|equilibrium with their ices]] on Pluto's surface.<ref name="NYT-20150724-ap">{{cite news |title=Conditions on Pluto: Incredibly Hazy With Flowing Ice |url=https://www.nytimes.com/aponline/2015/07/24/science/ap-us-sci-pluto.html |date=July 24, 2015 |work=[[New York Times]] |access-date=July 24, 2015 |archive-date=July 28, 2015 |archive-url=https://web.archive.org/web/20150728081402/http://www.nytimes.com/aponline/2015/07/24/science/ap-us-sci-pluto.html |url-status=live }}</ref><ref name="Croswell1992" /> According to the measurements by ''New Horizons'', the surface pressure is about 1&nbsp;[[Pascal (unit)|Pa]] (10&nbsp;[[μbar]]),<ref name=Stern2015 /> roughly one million to 100,000 times less than Earth's atmospheric pressure. It was initially thought that, as Pluto moves away from the Sun, its atmosphere should gradually freeze onto the surface; studies of ''New Horizons'' data and ground-based occultations show that Pluto's atmospheric density increases, and that it likely remains gaseous throughout Pluto's orbit.<ref name=Olkin_2015 /><ref name="skyandtel">{{cite news|title=Pluto's Atmosphere Confounds Researchers|author=Kelly Beatty|newspaper=Sky & Telescope|year=2016|url=http://www.skyandtelescope.com/astronomy-news/plutos-atmosphere-confounds-researchers-032520166/|access-date=April 2, 2016|archive-date=April 7, 2016|archive-url=https://web.archive.org/web/20160407162627/http://www.skyandtelescope.com/astronomy-news/plutos-atmosphere-confounds-researchers-032520166/|url-status=live}}</ref> ''New Horizons'' observations showed that atmospheric escape of nitrogen to be 10,000 times less than expected.<ref name=skyandtel /> Alan Stern has contended that even a small increase in Pluto's surface temperature can lead to exponential increases in Pluto's atmospheric density; from 18&nbsp;hPa to as much as 280&nbsp;hPa (three times that of Mars to a quarter that of the Earth). At such densities, nitrogen could flow across the surface as liquid.<ref name=skyandtel /> Just like sweat cools the body as it evaporates from the skin, the [[sublimation (phase transition)|sublimation]] of Pluto's atmosphere cools its surface.<ref name="KerThan2006-CNN" /> Pluto has no or almost no [[troposphere]]; observations by ''New Horizons'' suggest only a thin tropospheric [[planetary boundary layer|boundary layer]]. Its thickness in the place of measurement was 4&nbsp;km, and the temperature was 37±3 K. The layer is not continuous.<ref name=Gladstone_2016>{{cite journal |title=The atmosphere of Pluto as observed by New Horizons |last1=Gladstone |first1=G. R. |last2=Stern |first2=S. A. |last3=Ennico |first3=K. |display-authors=etal |date=March 2016 |journal=Science |volume=351 |issue=6279 |doi=10.1126/science.aad8866 |bibcode=2016Sci...351.8866G |arxiv=1604.05356 |url=https://www.astro.umd.edu/~dphamil/research/reprints/GlaSteEnn16.pdf |url-status=dead |archive-url=https://web.archive.org/web/20160521090831/https://www.astro.umd.edu/~dphamil/research/reprints/GlaSteEnn16.pdf |archive-date=May 21, 2016 |pages=aad8866 |pmid=26989258 |s2cid=32043359 |access-date=June 12, 2016}} ([https://web.archive.org/web/20160521191420/http://authors.library.caltech.edu/65692/2/Gladstone-SM.pdf Supplementary Material])</ref>

In July 2019, an occultation by Pluto showed that its atmospheric pressure, against expectations, had fallen by 20% since 2016.<ref>{{cite web|title=What is happening to Pluto's Atmosphere|url=https://astronomy.com/news/2020/05/plutos-strange-atmosphere-just-collapsed|date=May 22, 2020|access-date=October 7, 2021|archive-date=October 24, 2021|archive-url=https://web.archive.org/web/20211024063219/https://astronomy.com/news/2020/05/plutos-strange-atmosphere-just-collapsed|url-status=live}}</ref> In 2021, astronomers at the [[Southwest Research Institute]] confirmed the result using data from an occultation in 2018, which showed that light was appearing less gradually from behind Pluto's disc, indicating a thinning atmosphere.<ref>{{cite web|title=SwRI Scientists Confirm Decrease In Pluto's Atmospheric Density|url=https://www.swri.org/press-release/scientists-confirm-decrease-plutos-atmospheric-density|date=October 4, 2021|work=Southwest Research Institute|access-date=October 7, 2021|archive-date=October 15, 2021|archive-url=https://web.archive.org/web/20211015201003/https://www.swri.org/press-release/scientists-confirm-decrease-plutos-atmospheric-density|url-status=live}}</ref>

The presence of methane, a powerful [[greenhouse gas]], in Pluto's atmosphere creates a [[temperature inversion]], with the average temperature of its atmosphere tens of degrees warmer than its surface,<ref name=Lellouch_2009 /> though observations by ''New Horizons'' have revealed Pluto's upper atmosphere to be far colder than expected (70&nbsp;K, as opposed to about 100&nbsp;K).<ref name=skyandtel /> Pluto's atmosphere is divided into roughly 20 regularly spaced haze layers up to 150&nbsp;km high,<ref name=Stern2015 /> thought to be the result of pressure waves created by airflow across Pluto's mountains.<ref name=skyandtel />