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Atmosphere of Triton

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The atmosphere of Triton extends 800 kilometers above Triton's surface.[1] The atmosphere mainly is composed of nitrogen, similar to Titan's atmosphere and Earth's atmosphere.[2] The surface pressure is only 14 microbars, which is 1/70,000th of the surface pressure on Earth.[1] Originally, it was thought Triton had a thick atmosphere.[3] Voyager 2 observed the atmosphere up close in 1989. Recent observations of the atmosphere have shown an increase in temperature.[4]

Major components

Nitrogen is the main gas in Triton's atmosphere. Methane is also present.[5] Other planets and moons with similarly composed atmospheres include the atmosphere of Titan and the atmosphere of Earth.[2]

Structure

Triton's atmosphere is well structured and global.[6] The atmosphere extends 800 kilometers above the surface and has a surface pressure of 14 microbars. This is only 1/70,000th of the surface pressure on Earth.[1] The surface temperature is at least 35.6 K (−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.[7] An upper limit with kelvins in the low 40s can be set from vapor pressure equilibrium with nitrogen gas in Triton's atmosphere.[8] Turbulence at Triton's surface creates a troposphere (a "weather region") rising to an altitude of 8 km.[9] The atmosphere does not have a stratosphere.[10] Higher regions are divided into the thermosphere, the ionosphere, and the exosphere.[11] The exosphere has a temperature of 95 kelvins.

Weather

A cloud over the limb of Triton, taken by Voyager 2.

Nitrogen ice particles form clouds a few kilometers above the surface of Triton.[1] Haze has also been found.[12] this haze is believed to be composed largely of hydrocarbons and nitriles created by the action of sunlight on methane.[10] 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.[5] These winds flow to the west and are driven by differences in temperature between the poles and equator.[6] They are capable of moving material of over a micrometre in size.[9] The middle of the atmosphere is likely distorted by supersonic winds, indicated by Triton's light curve.[13] Winds in low altitudes in the southern hemisphere flow to the northeast.[6] Voyager 2 reported that a polar anticyclone forms, caused by subliming frost. The cyclone has wind speeds of about 5m s-1.[6]

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.[3]

Voyager 2

Five hours following closest approach to Neptune, Voyager 2 approached Triton in 1989.[14] During the flyby, Voyager 2 took measurements of the atmosphere,[15] finding methane and nitrogen in the atmosphere.[5]

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.[16] Other observations have shown an increase in temperature by 5% since 1989 to 1998.[4] The publisher of the report, James L. Elliot, said:[4]

"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.[17] 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.[18]

Triton Watch

The Triton Watch program uses astronomers to monitor changes in the atmosphere. It was created from funds from NASA.[19]

See also

References

  1. ^ a b c d "Triton". Voyager. Retrieved 2007-12-31.
  2. ^ a b "Neptune: Moons: Triton". Solar System Exploration. Retrieved 2007-12-31.
  3. ^ a b Lunine, J. I.; and Nolan, Michael C. (1992). "A massive early atmosphere on Triton". Icarus. 100: pp. 221–234. doi:10.1016/0019-1035(92)90031-2. {{cite journal}}: |pages= has extra text (help)CS1 maint: multiple names: authors list (link)
  4. ^ a b c "MIT researcher finds evidence of global warming on Neptune's largest moon". Massachusetts Institute of Technology. 1998-06-24. Retrieved 2007-12-31.
  5. ^ a b c Miller, Ron (2005). The Grand Tour: A Traveler's Guide to the Solar System (3rd edition ed.). Thailand: Workman Publishing. pp. 172–173. ISBN 0-7611-3547-2. {{cite book}}: |edition= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  6. ^ a b c d Ingersoll, Andrew P. (1990). "Dynamics of Triton's atmosphere". Nature. 344: pp. 315–317. doi:10.1038/344315a0. 10.1038/344315a. Retrieved 2008-04-12. {{cite journal}}: |pages= has extra text (help); Unknown parameter |month= ignored (help)
  7. ^ N S Duxbury, R H Brown (August 1993). "The Phase Composition of Triton's Polar Caps". Science. 261 (5122): 748–751. doi:10.1126/science.261.5122.748. ISSN 0036-8075. Retrieved 2008-01-24.
  8. ^ Kimberly Tryka, Robert Brown, V. Anicich; et al. (August 1993). "Spectroscopic Determination of the Phase Composition and Temperature of Nitrogen Ice on Triton". Science. 261 (5122): 751–754. doi:10.1126/science.261.5122.751. ISSN 0036-8075. Retrieved 2008-01-24. {{cite journal}}: Explicit use of et al. in: |author= (help)CS1 maint: multiple names: authors list (link)
  9. ^ a b B A Smith, L A Soderblom; et al. (December 15, 1989). "Voyager 2 at Neptune: Imaging Science Results". Science. 246: 1422–1449. doi:10.1126/science.246.4936.1422. ISSN 0036-8075. Retrieved 2008-01-15. {{cite journal}}: Explicit use of et al. in: |author= (help)
  10. ^ a b McKinnon, William B. "Triton". Encyclopedia of the Solar System (2nd. ed.). Academic Press. pp. 483–502. ISBN 0120885891. {{cite book}}: Cite has empty unknown parameter: |chapterurl= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  11. ^ Lellouch, E.; Blanc, M.; Oukbir J.; and Longaretti, P.-Y. (1992). "A model of Triton's atmosphere and ionosphere". Advances in Space Research. 12: pp. 113–121. doi:10.1016/0273-1177(92)90427-Y. {{cite journal}}: |pages= has extra text (help)CS1 maint: multiple names: authors list (link)
  12. ^ "Triton". nineplanets.org. Retrieved 2007-12-31.
  13. ^ Elliot, J. L. (1997). "Triton's Distorted Atmosphere". Science. 278: pp. 436–439. doi:10.1126/science.278.5337.436. 10.1126. Retrieved 2007-12-31. {{cite journal}}: |pages= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  14. ^ Wilford, John. "Profile of Neptune's Main Moon: Small, Bright, Cold, and It's Pink". The New York Times. Retrieved 2007-12-31.
  15. ^ "Triton: Background and Science". PLANETARY SCIENCE DIRECTORATE Boulder Office. Retrieved 2007-12-31.
  16. ^ Savage, D.; Weaver, D.; and Halber, D. "Hubble Space Telescope Helps Find Evidence that Neptune's Largest Moon Is Warming Up". Hubblesite. Retrieved 2007-12-31.{{cite web}}: CS1 maint: multiple names: authors list (link)
  17. ^ "Global Warming Detected on Triton". Scienceagogo.com. 1998-05-28. Retrieved 2007-12-31.
  18. ^ Buratti, Bonnie J. (1999-01-21). "Does global warming make Triton blush?" (PDF). Nature. 397 (6716): 219. doi:10.1038/16615. Retrieved 2007-12-31. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  19. ^ "About the Triton Watch Project". PLANETARY SCIENCE DIRECTORATE Boulder Office. Retrieved 2007-12-31.
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