Atmosphere of Triton

The atmosphere of Triton extends 800 kilometers above Triton's surface.cite web | url = http://voyager.jpl.nasa.gov/science/neptune_triton.html | title = Triton | work = Voyager | accessdate = 2007-12-31] The atmosphere mainly is composed of nitrogen, similar to Titan's atmosphere and Earth's atmosphere.cite web | url = http://solarsystem.nasa.gov/planets/profile.cfm?Object=Nep_Triton | title = Neptune: Moons: Triton | work = Solar System Exploration | accessdate = 2007-12-31] The surface pressure is only 14 microbars, which is 1/70,000th of the surface pressure on Earth. Originally, it was thought Triton had a thick atmosphere. Voyager 2 observed the atmosphere up close in 1989. Recent observations of the atmosphere have shown an increase in temperature.

Major components

Nitrogen is the main gas in Triton's atmosphere. Methane is also present.cite book |title=The Grand Tour: A Traveler's Guide to the Solar System|last= Miller|first= Ron|authorlink= Ron Miller (artist and author)|coauthors=William K. Hartmann|year= 2005|month= May|pages= 172-173|publisher= Workman Publishing|location= Thailand|edition= 3rd edition|isbn= 0-7611-3547-2] Other planets and moons with similarly composed atmospheres include the atmosphere of Titan and the atmosphere of Earth.

tructure

Triton's atmosphere is well structured and global. The atmosphere extends 800 kilometers above the surface and has a surface pressure is only 14 microbars. This is only 1/70,000th of the surface pressure on Earth. The surface temperature is at least nowrap|35.6 K nowrap|(−237.6 °C) because Triton's nitrogen ice is in the warmer, hexagonal crystalline state, and the phase transition between hexagonal and cubic nitrogen ice occurs at that temperature.cite journal
title = The Phase Composition of Triton's Polar Caps
url = http://adsabs.harvard.edu/abs/1993Sci...261..748D
author = N S Duxbury, R H Brown
journal = Science
issn = 0036-8075
volume = 261
issue = 5122
pages = 748–751
date = August 1993
accessdate = 2008-01-24
doi = 10.1126/science.261.5122.748] An upper limit with kelvins in the low 40s can be set from vapor pressure equilibrium with nitrogen gas in Triton's atmosphere. [cite journal
title = Spectroscopic Determination of the Phase Composition and Temperature of Nitrogen Ice on Triton
author= Kimberly Tryka, Robert Brown, V. Anicich et al.
journal = Science
issn = 0036-8075
volume = 261
issue = 5122
pages = 751–754
url = http://adsabs.harvard.edu/abs/1993Sci...261..751T
date = August 1993
accessdate = 2008-01-24
doi = 10.1126/science.261.5122.751] Turbulence at Triton's surface creates a troposphere (a "weather region") rising to an altitude of 8 km. The atmosphere does not have a stratosphere.cite book|last= McKinnon|first= William B.|coauthors= Randolph L. Kirk |title= Encyclopedia of the Solar System|origyear= 2007|edition= 2nd.|publisher= Academic Press|isbn= 0120885891|pages= 483–502|chapter= Triton|chapterurl= |quote= ] Higher regions are divided into the thermosphere, the ionosphere, and the exosphere.cite journal | doi = 10.1016/0273-1177(92)90427-Y| title = A model of Triton's atmosphere and ionosphere | author = Lellouch, E.; Blanc, M.; Oukbir J.; and Longaretti, P.-Y.| journal = Advances in Space Research| volume = 12| year = 1992| pages = pp. 113–121] The exosphere has a temperature of 95 kelvins.

Weather

Nitrogen ice particles form clouds a few kilometers above the surface of Triton. Haze has also been found.cite web|url=http://www.nineplanets.org/triton.html|title=Triton|work=nineplanets.org|accessdate=2007-12-31] this haze is believed to be composed largely of hydrocarbons and nitriles created by the action of sunlight on methane. Triton's atmosphere also possesses clouds of condensed nitrogen that lie between 1 and 3 km from the surface. Eight kilometers high in the atmosphere, high altitude prevailing winds are present. These winds flow to the west and are driven by differences in temperature between the poles and equator. They are capable of moving material of over a micrometre in size.cite journal
title = Voyager 2 at Neptune: Imaging Science Results
author = B A Smith, L A Soderblom et al.
journal = Science
issn = 0036-8075
volume = 246
pages = 1422–1449
date = December 15 1989
url = http://adsabs.harvard.edu/abs/1989Sci...246.1422S
accessdate = 2008-01-15
doi = 10.1126/science.246.4936.1422] The middle of the atmosphere is likely distorted by supersonic winds, indicated by Triton's light curve.cite journal|last=Elliot |first=J. L.|coauthors=J. A. Stansberry, C. B. Olkin, M. A. Agner, M. E. Davies |year= 1997|month=October |title=Triton's Distorted Atmosphere |journal= Science|volume= 278|pages= pp. 436–439|id=10.1126 |url= http://www.sciencemag.org/cgi/content/abstract/278/5337/436|accessdate= 2007-12-31 |doi=10.1126/science.278.5337.436] Winds in low altitudes in the southern hemisphere flow to the northeast.cite journal|last=Ingersoll |first=Andrew P. |year= 1990|month=March |title= Dynamics of Triton's atmosphere|journal= Nature|volume= 344|pages= pp. 315–317|id= 10.1038/344315a|url= http://www.nature.com/nature/journal/v344/n6264/abs/344315a0.html|accessdate= 2008-04-12 |doi= 10.1038/344315a0] Voyager 2 reported that a polar anticyclone forms, caused by subliming frost. The cyclone has wind speeds of about 5m s^-1.

Observations and exploration

Before Voyager 2

Before Voyager 2 arrived, a nitrogen and methane atmosphere with a density as much as 30% that of the Earth had been speculated. Similar to the overestimates of the atmospheric density of Mars, this was found to be completely false, but like on Mars, a denser early atmosphere is postulated.cite journal| doi= 10.1016/0019-1035(92)90031-2|title=A massive early atmosphere on Triton|author=Lunine, J. I.; and Nolan, Michael C.|journal= Icarus|volume= 100|year= 1992|pages= pp. 221–234]

Voyager 2

Five hours following closest approach to Neptune, Voyager 2 approached Triton in 1989.cite web|url=http://query.nytimes.com/gst/fullpage.html?res=950DE7DC113DF931A1575BC0A96F948260&sec=&spon=&pagewanted=all|title=Profile of Neptune's Main Moon: Small, Bright, Cold, and It's Pink|work=The New York Times|last=Wilford |first=John|accessdate=2007-12-31] During the flyby, Voyager 2 took measurements of the atmosphere,Cite web|url=http://www.boulder.swri.edu/TritonWatch/background.html|title=Triton: Background and Science|work=PLANETARY SCIENCE DIRECTORATE Boulder Office|accessdate=2007-12-31] finding methane and nitrogen in the atmosphere.

Later observations

In the 1990s, observations from Earth were made of the limb of Triton using the occultation of stars by Triton. These observations indicated the presence of a denser atmosphere than was thought from Voyager 2 data.cite web | url = http://hubblesite.org/newscenter/newsdesk/archive/releases/1998/23/text/ | title = Hubble Space Telescope Helps Find Evidence that Neptune's Largest Moon Is Warming Up | work = Hubblesite | author = Savage, D.; Weaver, D.; and Halber, D | accessdate = 2007-12-31] Other observations have shown an increase in temperature by 5% since 1989 to 1998.cite web| title=MIT researcher finds evidence of global warming on Neptune's largest moon | url=http://web.mit.edu/newsoffice/1998/triton.html | date=1998-06-24 | publisher=Massachusetts Institute of Technology | accessdate=2007-12-31] The publisher of the report, James L. Elliot, said:

"At least since 1989, Triton has been undergoing a period of global warming. Percentage-wise, it's a very large increase."

These observations indicate Triton is approaching an unusually warm summer season that only happens once every few hundred years. Theories for this warming include a change of frost patterns on Triton's surface and a change in ice albedo, which would allow more heat to be absorbed.cite web| title=Global Warming Detected on Triton | url=http://www.scienceagogo.com/news/19980526052143data_trunc_sys.shtml | date=1998-05-28 | publisher=Scienceagogo.com | accessdate=2007-12-31] Another theory argues the changes in temperature are a result of deposition of dark, red material from geological processes on the moon. Because Triton's Bond albedo is among the highest within the Solar System, it is sensitive to small variations in spectral albedo.cite journal| title=Does global warming make Triton blush? | url=http://www.bio.indiana.edu/~palmerlab/Journals/170.pdf | last=Buratti | first=Bonnie J. | coauthors=Michael D. Hicks, Ray L. Newburn Jr| journal=Nature | volume=397 | issue=6716 | date=1999-01-21 | pages=219 | doi=10.1038/16615 | format=PDF | accessdate=2007-12-31]

Triton Watch

The "Triton Watch" program uses astronomers to monitor changes in the atmosphere. It was created from funds from NASA.cite web|url=http://www.boulder.swri.edu/TritonWatch/about.html|title=About the Triton Watch Project|work=PLANETARY SCIENCE DIRECTORATE Boulder Office|accessdate=2007-12-31]

ee also

* Atmosphere
* Triton
* Voyager 2

References

External links

* [http://voyager.jpl.nasa.gov/ Voyager website]