The atmosphere of Pluto was first discovered in 1985, and many specifics have gradually been determined, although most details remain unconfirmed until more detailed study is possible. Current studies show the Pluto's atmosphere is composed mostly of nitrogen, with some methane, carbon monoxide, and ethane,[1][2] at a pressure of about 6.5 to 24 microbar (0.65 to 2.4 pascals (Pa)) at the surface.
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Features
The atmospheric pressure of the surface of Pluto is approximately 100,000th that of Earth, or about 0.015 millibar (mbar). One study in 2009 estimates the pressure in the 6.5-24 μbar range.[1]
It undergoes temperature inversion in that Pluto's upper atmosphere is about 50 degrees warmer (103 K or -170° C) than the surface (53 K or -220° C) while Pluto's lower atmosphere is 40 degrees warmer.
Pluto's upper atmosphere consists mostly of nitrogen, with traces of methane, and carbon monoxide derived from the ices on its surface,[3] while the lower atmosphere is methane rich.[4]
As Pluto moves away from the Sun, its atmosphere gradually freezes and falls to the ground. As it edges closer to the Sun, the temperature of Pluto's solid surface increases, causing the ices to sublimate into gas. This creates an anti-greenhouse effect; much like sweat cools the body as it evaporates from the surface of the skin, this sublimation has a cooling effect on the surface of Pluto. Scientists using the Submillimeter Array have recently discovered that Pluto's temperature is about 43 K (−230 °C), 10 K colder than expected.[5]
Discoveries
Pluto was found to have an atmosphere from an occultation observation in 1985; the finding was confirmed and significantly strengthened by extensive observations of another occultation in 1988. When an object with no atmosphere occults a star, the star abruptly disappears; in the case of Pluto, the star dimmed out gradually.[6] From the rate of dimming, the atmospheric pressure was determined to be 0.15 pascal, roughly 1/700,000 that of Earth.[7]
In 2002, another occultation of a star by Pluto was observed and analysed by teams led by Bruno Sicardy of the Paris Observatory,[8] James L. Elliot of MIT,[9] and Jay Pasachoff of Williams College.[10] The atmospheric pressure was estimated to be 0.3 pascal, even though Pluto was farther from the Sun than in 1988 and thus should have been colder and had a more rarefied atmosphere. One explanation for the discrepancy is that in 1987 the south pole of Pluto came out of shadow for the first time in 120 years, causing extra nitrogen to sublimate from the polar cap. It will take decades for the excess nitrogen to condense out of the atmosphere.[11] Another stellar occultation was observed by the MIT-Williams College team of James Elliot, Jay Pasachoff, and a Southwest Research Institute team led by Leslie Young on June 12, 2006 from sites in Australia.[12]
In October 2006, Dale Cruikshank of NASA/Ames Research Center (a New Horizons co-investigator) and his colleagues announced the spectroscopic discovery of ethane on Pluto's surface. This ethane is produced from the photolysis or radiolysis (i.e., the chemical conversion driven by sunlight and charged particles) of frozen methane on Pluto's surface and suspended in its atmosphere.[13]
See also
Notes
- ^ a b Lellouch, E.; Sicardy, B.; de Bergh, C.; Käufl, H. -U.; Kassi, S.; Campargue, A. (2009). "Pluto's lower atmosphere structure and methane abundance from high-resolution spectroscopy and stellar occultations". arΧiv: 0901.4882 [astro-ph.EP].
- ^ A. Stern (November 1, 2006). "Making Old Horizons New". The PI's Perspective. Johns Hopkins University Applied Physics Laboratory. http://pluto.jhuapl.edu/overview/piPerspectives/piPerspective_11_1_2006.php. Retrieved 2007-02-12.
- ^ K. Croswell (1992). "Nitrogen in Pluto's Atmosphere". http://www.kencroswell.com/NitrogenInPlutosAtmosphere.html. Retrieved 2007-04-27.
- ^ E. Lellouch, B. Sicardy, C. de Bergh (2009). "Pluto's lower atmosphere structure and methane abundance from high-resolution spectroscopy and stellar occultations" (in press). A&A.
- ^ T. Ker (2006). "Astronomers: Pluto colder than expected". Space.com (via CNN.com). http://www.cnn.com/2006/TECH/space/01/03/pluto.temp/index.html. Retrieved 2006-03-05.
- ^ "IAUC 4097". 1985. http://cfa-www.harvard.edu/iauc/04000/04097.html#Item0. Retrieved 2007-03-26.
- ^ R. Johnston (2006). "The atmospheres of Pluto and other trans-Neptunian objects". http://www.johnstonsarchive.net/astro/pluto.html. Retrieved 2007-03-26.
- ^ B. Sicardy; T. Widemann, et al. (2003-07-10). "Large changes in Pluto's atmosphere as revealed by recent stellar occultations". Nature (Nature) 424: 168. doi:.
- ^ "Pluto is undergoing global warming, researchers find". Massachusetts Institute of Technology. 2002-10-09. http://web.mit.edu/newsoffice/2002/pluto.html. Retrieved 2007-03-20.
- ^ "Williams Scientists Contribute to New Finding About Pluto". Williams College. 2003-07-09. http://www.williams.edu/admin/news/releases.php?id=162. Retrieved 2007-03-20.
- ^ R.R. Britt (2003). "Puzzling Seasons and Signs of Wind Found on Pluto". Space.com. http://www.space.com/scienceastronomy/pluto_seasons_030709.html. Retrieved 2007-03-26.
- ^ J.L. Elliot et al. (2006). "The Size of Pluto's Atmosphere As Revealed by the 2006 June 12 Occultation". E Pasadena Division of Planetary Sciences. http://adsabs.harvard.edu/abs/2006DPS....38.3102. Retrieved 2007-04-12.
- ^ A. Stern (November 1, 2006). "Making Old Horizons New". The PI's Perspective. Johns Hopkins University Applied Physics Laboratory. http://pluto.jhuapl.edu/overview/piPerspectives/piPerspective_11_1_2006.php. Retrieved 2007-02-12.
Further reading
- Constraints on the Structure of Pluto's Atmosphere; Slivan, S. M.; Dunham, E. W.; Bulletin of the American Astronomical Society, Vol. 21, p.986 Text (also "Pluto's interaction with the Solar Wind" (Bagenal & McNutt)
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