Difference between revisions of "Triton"
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| − | [[ | + | {{Planet |
| + | |image=Triton1_Voyager2.jpg | ||
| + | |caption=True-color image of Triton's south pole, by [[Voyager 2]] | ||
| + | |date=October 10, 1846<ref name=usgs>"[http://planetarynames.wr.usgs.gov/append7.html Gazetteer of Planetary Nomenclature: Planetary Body Names and Discoverers]." US Geological Survey, Jennifer Blue, ed. March 31, 2008. Accessed May 9, 2008.</ref> | ||
| + | |discname=William Lassell<ref name=usgs/><ref name=Hamilton>Hamilton, Calvin J. "[http://www.solarviews.com/eng/triton.htm Entry for Triton]." ''Views of the Solar System'', 1997. Accessed May 9, 2008.</ref> | ||
| + | |origname=Demigod and son of Poseidon and Amphitrite.<ref name=usgs/> | ||
| + | |primary=Neptune | ||
| + | |order=7 | ||
| + | |periapsis=354,754 km<ref name=calc>Calculated</ref> | ||
| + | |apoapsis=354,766 km<ref name=calc/> | ||
| + | |semimajor=354,760 km<ref name=neptunesatfact>[http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptuniansatfact.html Neptunian Satellite Fact Sheet], [[National Aeronautics and Space Administration|NASA]], January 22, 2008. Accessed May 9, 2008.</ref> | ||
| + | |eccentricity=0.000016<ref name=neptunesatfact/> | ||
| + | |sidereal=-5.876854 da<ref name=neptunesatfact/> | ||
| + | |inclination=157.345°<ref name=neptunesatfact/> | ||
| + | |siderealday=-5.876854 da<ref name=neptunesatfact/> | ||
| + | |axialtilt=0° | ||
| + | |mass=2.14 * 10<sup>22</sup> kg<ref name=neptunesatfact/> | ||
| + | |meanradius=1,353.4 km<ref name=neptunesatfact/> | ||
| + | |density=2,050 kg/m³<ref name=neptunesatfact/> | ||
| + | |surfacegrav=0.77955 m/s²<ref name=calc/> | ||
| + | |escapespeed=1.4526 km/s<ref name=calc/> | ||
| + | |surfacearea=23,017,715 km²<ref name=calc/> | ||
| + | |meantemp=34.5 K<ref name=Arnett>Arnett, Bill. "[http://www.nineplanets.org/triton.html Entry for Triton]." ''The <s>Nine</s> 8 Planets'', October 13, 1998. Accessed May 9, 2008.</ref> | ||
| + | |composition=25% [[water]] ice, 75% rock<ref name=Arnett/> | ||
| + | |color=Pinkish-white | ||
| + | |albedo=0.76<ref name=neptunesatfact/> | ||
| + | }}'''Triton''', or '''Neptune I''', is the seventh [[moon]] of [[Neptune]] in order of distance, the first moon of Neptune to be discovered, and the seventh largest moon in all the [[solar system]]. It is also the only moon that, while large enough to be called a [[dwarf planet]] were it not a satellite, revolves around its primary with a motion retrograde to the primary's own rotation about its axis. This remarkable object thus poses an interesting problem for [[uniformitarianism|uniformitarian]] [[astronomy|astronomical]] theories. | ||
| − | + | == Discovery == | |
| + | The [[United Kingdom|British]] astronomer [[William Laskell]] discovered Triton on October 10, 1846, less than one month following the discovery of Neptune itself.<ref name=Hamilton/><ref name=Arnett/> Laskell observed what he at first took to be a ring, but which later proved to be an artifact of the distortion that his new telescope produced. However, Laskell also observed a large satellite, and that image was ''not'' due to distortion.<ref name=apod>"[http://antwrp.gsfc.nasa.gov/apod/ap971123.html Triton: Neptune's Largest Moon]." ''Astronomy Picture of the Day'', [[National Aeronautics and Space Administration|NASA]], November 23, 1997. Accessed May 9, 2007.</ref> | ||
| + | Triton is named after a demigod of the sea, son of Poseidon and his lover Amphitrite. The [[France|French]] astronomer Camille Flammarion is credited with suggesting this name.<ref name=usgs/> For more than a century, Triton was the only satellite of Neptune known to man. | ||
| + | |||
| + | == Orbital characteristics == | ||
| + | The most remarkable characteristic of this object is its retrograde motion.<ref name=Hamilton/><ref name=Arnett/> Triton takes 5.876854 Julian days to complete one orbit about Neptune—in a direction opposite to Neptune's own rotation.<ref name=neptunesatfact/> This makes Triton unique among moons large enough for their self-gravity to force them into hydrostatic-equilibrium (that is, spheroidal) shape. Yet Titan's orbit is nearly circular; its eccentricity is the least of those of the thirteen satellites of Neptune and one of the lowest of the orbital eccentricities of all solar system objects.<ref name=neptunesatfact/> | ||
| + | |||
| + | == Rotational characteristics == | ||
| + | Triton is [[tidal locking|tidally locked]] and thus always keeps the same face toward Neptune. Thus its sidereal month and day are the same length, and furthermore its sidereal day is also retrograde. | ||
| + | |||
| + | == Physical characteristics == | ||
| + | Triton's mass is 2.14 * 10<sup>22</sup> kg, more than 29% that of [[Earth]]'s [[Moon]] and the seventh-largest mass of all the moons in the solar system. With a density of 2,050 kg/m³, it has far more rock and far less water ice than the core of Neptune.<ref name=Arnett/> | ||
| + | |||
| + | Triton is also the coldest object on record in the solar system, with a mean temperature of only 34.5 kelvins. This is probably due to Triton's unusually high geometric albedo, which causes it to reflect away energy from the Sun that it might otherwise absorb as heat.<ref name=Arnett/> Yet in the decade since Voyager 2's flyby of Triton in 1989, Triton's trace atmosphere thickened, and its mean temperature rose by two to three kelvins, a radical proportional warming. This was probably due to Triton's unusual orbital inclination, and the exposure of its south pole to more solar radiation than usual.<ref name=mit>"[http://web.mit.edu/newsoffice/1998/triton.html MIT researcher finds evidence of global warming on Neptune's largest moon]," [[Massachusetts Institute of Technology]], June 24, 1998. Accessed May 9, 2008.</ref> | ||
| + | |||
| + | Triton's surface is considered relatively young, not more than 10 million years by uniformitarian models.<ref name=Schenk>Schenk, Paul M., and Zahnle, Kevin. "[http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4PFW6FV-2&_user=10&_coverDate=12%2F01%2F2007&_rdoc=10&_fmt=summary&_orig=browse&_srch=doc-info(%23toc%236821%232007%23998079998%23674080%23FLA%23display%23Volume)&_cdi=6821&_sort=d&_docanchor=&_ct=19&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=cea35d4a7d94052a325123729f8dfcf0 On the Negligible Surface Age of Triton]." ''Icarus'', 192(1):135-149, December 1, 2007. <doi:10.1016/j.icarus.2007.07.004 > Accessed May 9, 2008.</ref> Geologists count 100 impact craters on the leading hemisphere (the one facing in the direction of its motion around Neptune) and suspect that debris from collisions involving the inner or outer moons of Neptune have struck Triton on this leading surface. | ||
| + | |||
| + | == Gallery == | ||
| + | <gallery> | ||
| + | Image:Triton.gif|Triton | ||
| + | Image:Triton2_Voyager2.jpg|Triton by Voyager 2 | ||
| + | </gallery> | ||
==References== | ==References== | ||
| + | {{reflist|2}} | ||
| + | == See also == | ||
John Gribbin, ''Companion to the Cosmos'' (Little, Brown & Company, 1996) | John Gribbin, ''Companion to the Cosmos'' (Little, Brown & Company, 1996) | ||
| − | |||
| − | |||
{{Solarsystem}} | {{Solarsystem}} | ||
[[Category: Astronomy]] | [[Category: Astronomy]] | ||
Revision as of 13:25, May 10, 2008
| Triton | |
|---|---|
 True-color image of Triton's south pole, by Voyager 2 | |
| Date of discovery | October 10, 1846[1] |
| Name of discoverer | William Lassell[1][2] |
| Name origin | Demigod and son of Poseidon and Amphitrite.[1] |
| Orbital characteristics | |
| Primary | Neptune |
| Order from primary | 7 |
| Periposeidion | 354,754 km[3] |
| Apoposeidion | 354,766 km[3] |
| Semi-major axis | 354,760 km[4] |
| Orbital eccentricity | 0.000016[4] |
| Sidereal month | |
| Inclination | 157.345°[4] to Neptune's equator |
| Rotational characteristics | |
| Sidereal day | -5.876854 da[4] |
| Axial tilt | 0° |
| Physical characteristics | |
| Mass | 2.14 * 1022 kg[4] |
| Density | 2,050 kg/m³[4] |
| Mean radius | 1,353.4 km[4] |
| Surface gravity | 0.77955 m/s²[3] |
| Escape speed | 1.4526 km/s[3] |
| Surface area | 23,017,715 km²[3] |
| Mean temperature | 34.5 K[5] |
| Composition | 25% water ice, 75% rock[5] |
| Color | Pinkish-white |
| Albedo | 0.76[4] |
Triton, or Neptune I, is the seventh moon of Neptune in order of distance, the first moon of Neptune to be discovered, and the seventh largest moon in all the solar system. It is also the only moon that, while large enough to be called a dwarf planet were it not a satellite, revolves around its primary with a motion retrograde to the primary's own rotation about its axis. This remarkable object thus poses an interesting problem for uniformitarian astronomical theories.
Discovery
The British astronomer William Laskell discovered Triton on October 10, 1846, less than one month following the discovery of Neptune itself.[2][5] Laskell observed what he at first took to be a ring, but which later proved to be an artifact of the distortion that his new telescope produced. However, Laskell also observed a large satellite, and that image was not due to distortion.[6]
Triton is named after a demigod of the sea, son of Poseidon and his lover Amphitrite. The French astronomer Camille Flammarion is credited with suggesting this name.[1] For more than a century, Triton was the only satellite of Neptune known to man.
Orbital characteristics
The most remarkable characteristic of this object is its retrograde motion.[2][5] Triton takes 5.876854 Julian days to complete one orbit about Neptune—in a direction opposite to Neptune's own rotation.[4] This makes Triton unique among moons large enough for their self-gravity to force them into hydrostatic-equilibrium (that is, spheroidal) shape. Yet Titan's orbit is nearly circular; its eccentricity is the least of those of the thirteen satellites of Neptune and one of the lowest of the orbital eccentricities of all solar system objects.[4]
Rotational characteristics
Triton is tidally locked and thus always keeps the same face toward Neptune. Thus its sidereal month and day are the same length, and furthermore its sidereal day is also retrograde.
Physical characteristics
Triton's mass is 2.14 * 1022 kg, more than 29% that of Earth's Moon and the seventh-largest mass of all the moons in the solar system. With a density of 2,050 kg/m³, it has far more rock and far less water ice than the core of Neptune.[5]
Triton is also the coldest object on record in the solar system, with a mean temperature of only 34.5 kelvins. This is probably due to Triton's unusually high geometric albedo, which causes it to reflect away energy from the Sun that it might otherwise absorb as heat.[5] Yet in the decade since Voyager 2's flyby of Triton in 1989, Triton's trace atmosphere thickened, and its mean temperature rose by two to three kelvins, a radical proportional warming. This was probably due to Triton's unusual orbital inclination, and the exposure of its south pole to more solar radiation than usual.[7]
Triton's surface is considered relatively young, not more than 10 million years by uniformitarian models.[8] Geologists count 100 impact craters on the leading hemisphere (the one facing in the direction of its motion around Neptune) and suspect that debris from collisions involving the inner or outer moons of Neptune have struck Triton on this leading surface.
Gallery
Triton
Triton by Voyager 2
References
- ↑ 1.0 1.1 1.2 1.3 "Gazetteer of Planetary Nomenclature: Planetary Body Names and Discoverers." US Geological Survey, Jennifer Blue, ed. March 31, 2008. Accessed May 9, 2008.
- ↑ 2.0 2.1 2.2 Hamilton, Calvin J. "Entry for Triton." Views of the Solar System, 1997. Accessed May 9, 2008.
- ↑ 3.0 3.1 3.2 3.3 3.4 Calculated
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 Neptunian Satellite Fact Sheet, NASA, January 22, 2008. Accessed May 9, 2008.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Arnett, Bill. "Entry for Triton." The
Nine8 Planets, October 13, 1998. Accessed May 9, 2008. - ↑ "Triton: Neptune's Largest Moon." Astronomy Picture of the Day, NASA, November 23, 1997. Accessed May 9, 2007.
- ↑ "MIT researcher finds evidence of global warming on Neptune's largest moon," Massachusetts Institute of Technology, June 24, 1998. Accessed May 9, 2008.
- ↑ Schenk, Paul M., and Zahnle, Kevin. "On the Negligible Surface Age of Triton." Icarus, 192(1):135-149, December 1, 2007. <doi:10.1016/j.icarus.2007.07.004 > Accessed May 9, 2008.
See also
John Gribbin, Companion to the Cosmos (Little, Brown & Company, 1996)
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