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{{Planet
| name=Titan
| image=Titan Cassini 2006.jpg
| caption=Titan in true color. The color is of Titan's hazy [[atmosphere]].<ref name=Cassini>"[http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1992 Titanic complexity]," Space Science Institute, [[Jet Propulsion Laboratory]], [[NASA]], February 13, 2006. Accessed February 16, 2008.</ref>
| date=March 25, 1655<ref name=solarviews>Hamilton, Calvin J. "[http://solarviews.com/eng/titan.htm Saturn's Moon Titan]." ''SolarViews'', 2001. Accessed February 16, 2008.</ref>
| discname=[[Christiaan Huygens]]<ref name=solarviews/><ref name=Huygens1>"[http://www.esa.int/esaSC/SEMJRT57ESD_index_0.html Discoverer of Titan: Christiaan Huygens.]" ''ESA Space Science'', [[European Space Agency]], April 24, 2007. Accessed February 16, 2008.</ref>
| origname=First generation of Greco-Roman gods
| primary=Saturn
| order=20
| periapsis=1,186,680 km<ref name=calc>Calculated</ref>
| apoapsis=1,257,060 km<ref name=calc/>
| semimajor=1,221,870 km<ref name=ssdelem>"[http://ssd.jpl.nasa.gov/?sat_elem Planetary Satellite Mean Orbital Parameters]," Solar System Dynamics, [[JPL]], [[NASA]]. Accessed February 16, 2008.</ref>
| eccentricity=0.0288<ref name=ssdelem>
| sidereal=15.85 da<ref name=ssdelem>
| synodic=
| orbitspeed=5.58 km/s<ref name=solarviews/>
| inclination=
| reference=
| siderealday=15.85 da<ref name=solarviews/>
| solarday=
| rotatespeed=
| axialtilt=0°
| mass=1.34553 * 10<sup>23</sup> kg (2.25157% earth)<ref name=calc/>
| density=1,880 kg/m³<ref name=ssdphys>"[http://ssd.jpl.nasa.gov/?sat_phys_par Planetary Satellite Physical Parameters]." Solar System Dynamics, [[JPL]], [[NASA]]. Accessed February 16, 2008.</ref>
| meanradius=2,575.5 km<ref name=ssdphys/>
| surfacegrav=1.3535 m/s² (0.13802 ''g'')<ref name=calc/>
| escapespeed=2.6405 km/s<ref name=calc/>
| surfacearea=83,355,253 km² (16.352% earth)<ref name=calc/>
| meantemp=95 K<ref name=solarviews/>
| composition=Rock, water ice, and hydrocarbons
| color=Orange<ref name=Cassini/>
| albedo=0.21<ref name=ssdphys/>
}}'''Titan''' ([[Greek]] Τῑτάν first-generation god) is the largest [[satellite]] of [[Saturn]], the second-largest planetary satellite in the [[solar system]] (after [[Ganymede]]), and the only body other than [[Earth]] to have stable bodies of liquid on its surface. Titan is twentieth in order from Saturn and the sixth satellite of [[dwarf planet]] size (consistent with its official [[International Astronomical Union|IAU]] catalog designation as "Saturn VI").
Until 2005, Titan was regarded as the only natural satellite in the [[solar system]] to have a true [[atmosphere]]. But the [[Cassini-Huygens mission]] has already demonstrated that Saturn's inner moon [[Enceladus]] ''also'' has an atmosphere, believed composed of ionized [[water]] vapor from repeated eruptions from [[volcano]]es and/or [[geyser]]s on its surface. This "atmosphere" is constantly escaping from Enceladus, perhaps to persist as the E ring of Saturn's ring system. Thus it requires a continuous source of replenishment. The theories of Enceladus' volcanic and/or geothermal activity are an attempt to explain this replenishment.<ref name=encelatm>"[http://www.esa.int/SPECIALS/Cassini-Huygens/SEM9RC2IU7E_0.html Cassini finds atmosphere on Enceladus]." ''ESA Cassini-Huygens]], March 16, 2005. Accessed February 16, 2008.</ref>
The most exciting finds on Titan to date are the liquid hydrocarbon "seas," containing among them more hydrocarbons than the entire proved reserves of [[oil]] and [[natural gas]] on earth.<ref name=Corsi>Corsi, Jerome R. "[http://www.worldnetdaily.com/index.php?fa=PAGE.view&pageId=56480 New data: Maybe oil isn't from dead dinos]." ''WorldNetDaily'', February 15, 2008. Accessed February 16, 2008.</ref>
== Discovery and naming==
The [[Netherlands|Dutch]] astronomer [[Christiaan Huygens]]<ref name=Huygens1/> first discovered Titan on March 25, 1655. He used a telescope far more refined than the one that [[Galileo Galilei]] had earlier used to discover four of the moons of [[Jupiter]].<ref name=VanHelden>Van Helden, Albert. "[http://www.sil.si.edu/silpublications/dibner-library-lectures/2004-VanHelden/2004_VanHelden.pdf Huygens's Rings, Cassini's Division, & Saturn's Children]." Dibner Library Lecture, October 27, 2004. Accessed February 16, 2008.</ref> This was the first of Saturn's moons to be discovered, so Huygens named the object he found ''Saturni Luna'' ([[Latin]] for "Saturn's moon"). [[Giovanni Domenico Cassini]] and other astronomers would eventually discover eight more moons of Saturn, including at least five inside of Titan. With Cassini's discoveries of the first four of these, Titan's name was changed to "Saturn IV." Titan now bears the catalog designation of "Saturn VI," the identifier that the [[International Astronomical Union]] has now assigned it. Recent deep-space robotic missions have discovered that a total of nineteen moons orbit inside Titan, and another thirty-two outside it.
Titan got its common name from [[John Herschel]] (son of the astronomer [[William Herschel]]). He gave Titan a generic name for the [[Titan]]s of mythology, and also named the other seven moons then known after specific deities among the Titans.<ref>Lassell, "[http://adsabs.harvard.edu//full/seri/MNRAS/0008//0000042.000.html Satellites of Saturn]," ''Monthly Notices of the Royal Astronomical Society'', 8:42, November 12, 1847. Accessed February 16, 2008.</ref>
== Orbital and rotational characteristics ==
Titan follows a slightly eccentric orbit at a mean distance of 1.22 million kilometers from Saturn's center (or rather, the [[barycenter]] of the Saturnian system). Its sidereal month is 15.85 Julian days, as is the length of its sidereal day. Astronomers therefore consider it in tidal lock with Saturn.
Titan is also in a 3:4 orbital resonance with the satellite [[Hyperion]], the next farther satellite in the Saturnian system.
== Physical characteristics ==
Titan is slightly larger in radius than [[Mercury]] (and [[Earth]]'s [[Moon]]), and is more massive than any of the [[dwarf planets]] [[Eris]], [[Pluto]], and [[Ceres]] by one to two orders of magnitude. Titan was once thought to be the broadest of all satellites, but the [[Voyager 1]] probe showed that Titan's large apparent diameter was due to its atmosphere, and in fact [[Ganymede]] is slightly larger in radius than is Titan.<ref name=Arnett>Arnett, Bill. "[http://www.nineplanets.org/titan.html Entry for Titan]." ''The <s>Nine</s> 8 Planets'', May 27, 2005. Accessed February 16, 2008</ref>.
Titan's bulk is probably half water ice and half rock, in several layers with a rock center and several layers of various crystalline forms of ice.<ref name=Arnett/>
== Atmosphere ==
The atmosphere of Titan is probably its most salient distinguishing feature. Its pressure at the surface is 1.6 times that at sea level on Earth, or roughly the pressure at the depth of an average swimming pool.<ref name=nasa2>"[http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Titan Entry for Titan]." ''Solar System Exploration'', [[NASA]], September 7, 2007. Accessed February 16, 2008.</ref> This atmosphere is composed chiefly of [[nitrogen]] and various hydrocarbon compounds that give Titan its orange color.<ref name=solarviews/>
The constituents of Titan's atmosphere are listed in this table:<ref name=ESAatm>"[http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31187 Entry for Titan's Atmosphere]." ''Cassini-Huygens mission'', [[European Space Agency]], February 15, 2005.</ref>
{| class="wikitable"
|-
! Name
! Formula
! Concentration
|-
| ''Major constituents''
|
| Percent
|-
| [[Nitrogen]]
| N<sub>2</sub>
| 87-99
|-
| [[Argon]]
| Ar
| 0-6
|-
| [[Methane]]
| CH<sub>4</sub>
| 1-6
|-
| ''Minor constituents''
|
| ppm
|-
| [[Hydrogen]]
| H<sub>2</sub>
| 2000
|-
| [[Ethane]]
| CH<sub>3</sub>CH<sub>3</sub>
| 20
|-
| [[Acetylene]]
| HC#CH
| 4
|-
| [[Ethylene]]
| H<sub>2</sub>C=CH<sub>2</sub>
| 1
|-
| [[Propane]]
| CH<sub>3</sub>CH<sub>2</sub>CH<sub>3</sub>
| 1
|-
| [[Methylacetylene]]
| H<sub>3</sub>CC#CH
| 0.03
|-
| [[Diacetylene]]
| HC#C-C#CH
| 0.02
|-
| Hydrogen [[cyanide]]
| HC#N
| 1
|-
| [[Cyanogen]]
| N#C-C#N
| 0.02
|-
| [[Cyanoacetylene]]
| HC#C-C#N
| 0.03
|-
| [[Acetonitrile]]
| H<sub>3</sub>C-C#N
| 0.003
|-
| [[Carbon monoxide]]
| C=O
| 50
|-
| [[Carbon dioxide]]
| O=C=O
| 0.01
|}
The argon finding is significant because much of it is <sup>40</sup>Ar, an isotope usually associated with volcanism. The currently favored interpretation is that Titan has multiple "cryovolcanos" that erupt with water ice and ammonia.<ref name=HuygensFindings>"[http://www.esa.int/SPECIALS/Cassini-Huygens/SEMHB881Y3E_0.html Seeing, touching and smelling the extraordinarily Earth-like world of Titan]." ''Cassini-Huygens project'', [[European Space Agency]], January 21, 2005. Accessed February 16, 2008.</ref>
The atmosphere is not of uniform composition. Clouds, presumably of methane, do form. Furthermore, Huygens' images of the surface show clear signs of erosion and formations that look like dry riverbeds, a sign that rain occurs--though the rain is of methane, not water.<ref name=Arnett/> However, the data do ''not'' indicate the looked-for "ocean" of methane, but rather indicate something akin to the seasonal rivers and lakes seen on earth.<ref name=Arnett/><ref name=HuygensFindings/>
== The Prebiotic-Abiotic Controversy ==
Before the launch of the [[Cassini-Huygens mission]] (see below), speculation on whether Titan had the required elements for [[abiogenesis]] were rife.<ref name=solarviews/> Specifically, scientists believed that the [[methane]] in Titan's atmosphere would combine photochemically to yield [[ethane]], [[ethylene]] (ethene), [[acetylene]] (ethyne), and hydrogen [[cyanide]], and thus form [[amino acid]]s.<ref name=solarviews/><ref name=nasa2/>
The Huygens lander has thus far found no biological process, though it has found the suspected constituents, and more. But gas-chromatograph mass spectrophotometric findings have also shown that the bulk of the methane on Titan is actually <sup>13</sup>C methane--not the <sup>12</sup>C methane that one would normally expect from biological processes.<ref name=Goddard>"[http://www.spaceref.com/news/viewpr.html?pid=18410 Titan's Mysterious Methane Comes From Inside, Not The Surface]." Press release, [[Goddard Space Flight Center]], [[NASA]], November 30, 2005. Accessed February 16, 2008, from <http://www.spaceref.com/></ref> Scientists at the Goddard Space Flight Center conclude that this methane is vented to the surface from a supply that was somehow trapped deep beneath the surface when Titan was formed. Furthermore, this lends further support to Thomas Gold's 1998 hypothesis that Earth's own supplies of oil and natural gas are in fact abiotic in origin.<ref name=Corsi2>"[http://www.worldnetdaily.com/news/article.asp?ARTICLE_ID=47675 'Fossil fuel' theory takes hit with NASA finding]." ''WorldNetDaily'', December 1, 2005. Accessed February 16, 2008.</ref>
This latest finding militates against the speculation that life might exist on Titan. Many scientists believe that Titan's chemistry and physical features are of a type that could have given rise to the earliest chemicals required for [[life]], had Titan been much closer to the [[Sun]] than it actually is. That speculation predates the Cassini-Huygens mission and includes a model suggesting that Titan harbored a vast underground reservoir of [[ammonia]] solution.<ref name=Fortes>Fortes, A. B. "[http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-45FC0TP-26&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=aa73d6642eb13527397bbec9ff9ca535 Exobiological Implications of a Possible Water-Ammonia Ocean Inside Titan]." ''Icarus'', 146(2):444-452, August 2000. Accessed February 16, 2008. [http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6WGF-45FC0TP-26-1&_cdi=6821&_user=10&_orig=search&_coverDate=08%2F31%2F2000&_sk=998539997&view=c&wchp=dGLbVlb-zSkWz&md5=644f3640a5d78afc50f8e4e50a4a09d2&ie=/sdarticle.pdf Full text] available to subscribers or for a fee.</ref> That particular model depended on the methane and the cyanide being biogenic, but as has been noted above, the methane certainly is ''not'' biogenic. The ammonia-water "[[aquifer]]" might yet exist, however, if the <sup>40</sup>Ar findings are a reliable indicator.<ref name=HuygensFindings/>
== Observation and Exploration ==
In the 300-plus years since its discovery, the only study of Titan was by observation with Earth-based telescopes. [[Pioneer 11]] made a brief flyby of Saturn in 1979 and took several low-quality images. [[Voyager 1]] and [[Voyager 2]] were next to visit Saturn in 1980 and 1981; Voyager 1 did make a close flyby of Titan, but its instruments could not penetrate the thick haze of the Titanian atmosphere.<ref name=solarviews/>
In 1994 the [[Hubble Space Telescope]] took photographs of an apparent "continent" on the Saturnian face of Titan.<ref name=nasa2/>
The first truly comprehensive study of that system is the [[Cassini-Huygens mission]], which launched on October 15, 2007 and arrived in the Saturnian system on July 1, 2004.<ref name=solarviews/> The major innovation of this mission was the use of radar equipment aboard the orbiter and the lander, to penetrate the haze.
Huygens was designed to land, and to study the atmosphere and the surface in detail on the way down. Huygens landed fully functional on Titan on January 14, 2005. It remained functional for three hours while it sent back many images and much data on the composition, including the carbon-isotopic ratio, of the Titanian atmosphere.
== Gallery ==
<gallery>
Image:Titan Saturn transit 2007.jpg|Titan transits Saturn just south of the ring plane
Image:Titan haze 2007.jpg|Titan's hazy atmosphere in ultraviolet light
Image:Titan mosaics 2006.jpg|Three false-color mosaics of Titan showing changes in its atmosphere within three months
Image:Titan surface approach 1.jpg|Surface of Titan from 17 to 8 km up, from Huygens lander as it descended
Image:Titan surface approach 2.jpg|Surface of Titan from 7 to 0.5 km up, from Huygens lander as it descended
Image:Titan landing.jpg|Surface of Titan, from Huygens lander after it landed
Image:Titan landing color.jpg|Surface of Titan, in color, from Huygens lander
</gallery>
== References ==
{{reflist|2}}
{{Solarsystem}}
| name=Titan
| image=Titan Cassini 2006.jpg
| caption=Titan in true color. The color is of Titan's hazy [[atmosphere]].<ref name=Cassini>"[http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1992 Titanic complexity]," Space Science Institute, [[Jet Propulsion Laboratory]], [[NASA]], February 13, 2006. Accessed February 16, 2008.</ref>
| date=March 25, 1655<ref name=solarviews>Hamilton, Calvin J. "[http://solarviews.com/eng/titan.htm Saturn's Moon Titan]." ''SolarViews'', 2001. Accessed February 16, 2008.</ref>
| discname=[[Christiaan Huygens]]<ref name=solarviews/><ref name=Huygens1>"[http://www.esa.int/esaSC/SEMJRT57ESD_index_0.html Discoverer of Titan: Christiaan Huygens.]" ''ESA Space Science'', [[European Space Agency]], April 24, 2007. Accessed February 16, 2008.</ref>
| origname=First generation of Greco-Roman gods
| primary=Saturn
| order=20
| periapsis=1,186,680 km<ref name=calc>Calculated</ref>
| apoapsis=1,257,060 km<ref name=calc/>
| semimajor=1,221,870 km<ref name=ssdelem>"[http://ssd.jpl.nasa.gov/?sat_elem Planetary Satellite Mean Orbital Parameters]," Solar System Dynamics, [[JPL]], [[NASA]]. Accessed February 16, 2008.</ref>
| eccentricity=0.0288<ref name=ssdelem>
| sidereal=15.85 da<ref name=ssdelem>
| synodic=
| orbitspeed=5.58 km/s<ref name=solarviews/>
| inclination=
| reference=
| siderealday=15.85 da<ref name=solarviews/>
| solarday=
| rotatespeed=
| axialtilt=0°
| mass=1.34553 * 10<sup>23</sup> kg (2.25157% earth)<ref name=calc/>
| density=1,880 kg/m³<ref name=ssdphys>"[http://ssd.jpl.nasa.gov/?sat_phys_par Planetary Satellite Physical Parameters]." Solar System Dynamics, [[JPL]], [[NASA]]. Accessed February 16, 2008.</ref>
| meanradius=2,575.5 km<ref name=ssdphys/>
| surfacegrav=1.3535 m/s² (0.13802 ''g'')<ref name=calc/>
| escapespeed=2.6405 km/s<ref name=calc/>
| surfacearea=83,355,253 km² (16.352% earth)<ref name=calc/>
| meantemp=95 K<ref name=solarviews/>
| composition=Rock, water ice, and hydrocarbons
| color=Orange<ref name=Cassini/>
| albedo=0.21<ref name=ssdphys/>
}}'''Titan''' ([[Greek]] Τῑτάν first-generation god) is the largest [[satellite]] of [[Saturn]], the second-largest planetary satellite in the [[solar system]] (after [[Ganymede]]), and the only body other than [[Earth]] to have stable bodies of liquid on its surface. Titan is twentieth in order from Saturn and the sixth satellite of [[dwarf planet]] size (consistent with its official [[International Astronomical Union|IAU]] catalog designation as "Saturn VI").
Until 2005, Titan was regarded as the only natural satellite in the [[solar system]] to have a true [[atmosphere]]. But the [[Cassini-Huygens mission]] has already demonstrated that Saturn's inner moon [[Enceladus]] ''also'' has an atmosphere, believed composed of ionized [[water]] vapor from repeated eruptions from [[volcano]]es and/or [[geyser]]s on its surface. This "atmosphere" is constantly escaping from Enceladus, perhaps to persist as the E ring of Saturn's ring system. Thus it requires a continuous source of replenishment. The theories of Enceladus' volcanic and/or geothermal activity are an attempt to explain this replenishment.<ref name=encelatm>"[http://www.esa.int/SPECIALS/Cassini-Huygens/SEM9RC2IU7E_0.html Cassini finds atmosphere on Enceladus]." ''ESA Cassini-Huygens]], March 16, 2005. Accessed February 16, 2008.</ref>
The most exciting finds on Titan to date are the liquid hydrocarbon "seas," containing among them more hydrocarbons than the entire proved reserves of [[oil]] and [[natural gas]] on earth.<ref name=Corsi>Corsi, Jerome R. "[http://www.worldnetdaily.com/index.php?fa=PAGE.view&pageId=56480 New data: Maybe oil isn't from dead dinos]." ''WorldNetDaily'', February 15, 2008. Accessed February 16, 2008.</ref>
== Discovery and naming==
The [[Netherlands|Dutch]] astronomer [[Christiaan Huygens]]<ref name=Huygens1/> first discovered Titan on March 25, 1655. He used a telescope far more refined than the one that [[Galileo Galilei]] had earlier used to discover four of the moons of [[Jupiter]].<ref name=VanHelden>Van Helden, Albert. "[http://www.sil.si.edu/silpublications/dibner-library-lectures/2004-VanHelden/2004_VanHelden.pdf Huygens's Rings, Cassini's Division, & Saturn's Children]." Dibner Library Lecture, October 27, 2004. Accessed February 16, 2008.</ref> This was the first of Saturn's moons to be discovered, so Huygens named the object he found ''Saturni Luna'' ([[Latin]] for "Saturn's moon"). [[Giovanni Domenico Cassini]] and other astronomers would eventually discover eight more moons of Saturn, including at least five inside of Titan. With Cassini's discoveries of the first four of these, Titan's name was changed to "Saturn IV." Titan now bears the catalog designation of "Saturn VI," the identifier that the [[International Astronomical Union]] has now assigned it. Recent deep-space robotic missions have discovered that a total of nineteen moons orbit inside Titan, and another thirty-two outside it.
Titan got its common name from [[John Herschel]] (son of the astronomer [[William Herschel]]). He gave Titan a generic name for the [[Titan]]s of mythology, and also named the other seven moons then known after specific deities among the Titans.<ref>Lassell, "[http://adsabs.harvard.edu//full/seri/MNRAS/0008//0000042.000.html Satellites of Saturn]," ''Monthly Notices of the Royal Astronomical Society'', 8:42, November 12, 1847. Accessed February 16, 2008.</ref>
== Orbital and rotational characteristics ==
Titan follows a slightly eccentric orbit at a mean distance of 1.22 million kilometers from Saturn's center (or rather, the [[barycenter]] of the Saturnian system). Its sidereal month is 15.85 Julian days, as is the length of its sidereal day. Astronomers therefore consider it in tidal lock with Saturn.
Titan is also in a 3:4 orbital resonance with the satellite [[Hyperion]], the next farther satellite in the Saturnian system.
== Physical characteristics ==
Titan is slightly larger in radius than [[Mercury]] (and [[Earth]]'s [[Moon]]), and is more massive than any of the [[dwarf planets]] [[Eris]], [[Pluto]], and [[Ceres]] by one to two orders of magnitude. Titan was once thought to be the broadest of all satellites, but the [[Voyager 1]] probe showed that Titan's large apparent diameter was due to its atmosphere, and in fact [[Ganymede]] is slightly larger in radius than is Titan.<ref name=Arnett>Arnett, Bill. "[http://www.nineplanets.org/titan.html Entry for Titan]." ''The <s>Nine</s> 8 Planets'', May 27, 2005. Accessed February 16, 2008</ref>.
Titan's bulk is probably half water ice and half rock, in several layers with a rock center and several layers of various crystalline forms of ice.<ref name=Arnett/>
== Atmosphere ==
The atmosphere of Titan is probably its most salient distinguishing feature. Its pressure at the surface is 1.6 times that at sea level on Earth, or roughly the pressure at the depth of an average swimming pool.<ref name=nasa2>"[http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Titan Entry for Titan]." ''Solar System Exploration'', [[NASA]], September 7, 2007. Accessed February 16, 2008.</ref> This atmosphere is composed chiefly of [[nitrogen]] and various hydrocarbon compounds that give Titan its orange color.<ref name=solarviews/>
The constituents of Titan's atmosphere are listed in this table:<ref name=ESAatm>"[http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31187 Entry for Titan's Atmosphere]." ''Cassini-Huygens mission'', [[European Space Agency]], February 15, 2005.</ref>
{| class="wikitable"
|-
! Name
! Formula
! Concentration
|-
| ''Major constituents''
|
| Percent
|-
| [[Nitrogen]]
| N<sub>2</sub>
| 87-99
|-
| [[Argon]]
| Ar
| 0-6
|-
| [[Methane]]
| CH<sub>4</sub>
| 1-6
|-
| ''Minor constituents''
|
| ppm
|-
| [[Hydrogen]]
| H<sub>2</sub>
| 2000
|-
| [[Ethane]]
| CH<sub>3</sub>CH<sub>3</sub>
| 20
|-
| [[Acetylene]]
| HC#CH
| 4
|-
| [[Ethylene]]
| H<sub>2</sub>C=CH<sub>2</sub>
| 1
|-
| [[Propane]]
| CH<sub>3</sub>CH<sub>2</sub>CH<sub>3</sub>
| 1
|-
| [[Methylacetylene]]
| H<sub>3</sub>CC#CH
| 0.03
|-
| [[Diacetylene]]
| HC#C-C#CH
| 0.02
|-
| Hydrogen [[cyanide]]
| HC#N
| 1
|-
| [[Cyanogen]]
| N#C-C#N
| 0.02
|-
| [[Cyanoacetylene]]
| HC#C-C#N
| 0.03
|-
| [[Acetonitrile]]
| H<sub>3</sub>C-C#N
| 0.003
|-
| [[Carbon monoxide]]
| C=O
| 50
|-
| [[Carbon dioxide]]
| O=C=O
| 0.01
|}
The argon finding is significant because much of it is <sup>40</sup>Ar, an isotope usually associated with volcanism. The currently favored interpretation is that Titan has multiple "cryovolcanos" that erupt with water ice and ammonia.<ref name=HuygensFindings>"[http://www.esa.int/SPECIALS/Cassini-Huygens/SEMHB881Y3E_0.html Seeing, touching and smelling the extraordinarily Earth-like world of Titan]." ''Cassini-Huygens project'', [[European Space Agency]], January 21, 2005. Accessed February 16, 2008.</ref>
The atmosphere is not of uniform composition. Clouds, presumably of methane, do form. Furthermore, Huygens' images of the surface show clear signs of erosion and formations that look like dry riverbeds, a sign that rain occurs--though the rain is of methane, not water.<ref name=Arnett/> However, the data do ''not'' indicate the looked-for "ocean" of methane, but rather indicate something akin to the seasonal rivers and lakes seen on earth.<ref name=Arnett/><ref name=HuygensFindings/>
== The Prebiotic-Abiotic Controversy ==
Before the launch of the [[Cassini-Huygens mission]] (see below), speculation on whether Titan had the required elements for [[abiogenesis]] were rife.<ref name=solarviews/> Specifically, scientists believed that the [[methane]] in Titan's atmosphere would combine photochemically to yield [[ethane]], [[ethylene]] (ethene), [[acetylene]] (ethyne), and hydrogen [[cyanide]], and thus form [[amino acid]]s.<ref name=solarviews/><ref name=nasa2/>
The Huygens lander has thus far found no biological process, though it has found the suspected constituents, and more. But gas-chromatograph mass spectrophotometric findings have also shown that the bulk of the methane on Titan is actually <sup>13</sup>C methane--not the <sup>12</sup>C methane that one would normally expect from biological processes.<ref name=Goddard>"[http://www.spaceref.com/news/viewpr.html?pid=18410 Titan's Mysterious Methane Comes From Inside, Not The Surface]." Press release, [[Goddard Space Flight Center]], [[NASA]], November 30, 2005. Accessed February 16, 2008, from <http://www.spaceref.com/></ref> Scientists at the Goddard Space Flight Center conclude that this methane is vented to the surface from a supply that was somehow trapped deep beneath the surface when Titan was formed. Furthermore, this lends further support to Thomas Gold's 1998 hypothesis that Earth's own supplies of oil and natural gas are in fact abiotic in origin.<ref name=Corsi2>"[http://www.worldnetdaily.com/news/article.asp?ARTICLE_ID=47675 'Fossil fuel' theory takes hit with NASA finding]." ''WorldNetDaily'', December 1, 2005. Accessed February 16, 2008.</ref>
This latest finding militates against the speculation that life might exist on Titan. Many scientists believe that Titan's chemistry and physical features are of a type that could have given rise to the earliest chemicals required for [[life]], had Titan been much closer to the [[Sun]] than it actually is. That speculation predates the Cassini-Huygens mission and includes a model suggesting that Titan harbored a vast underground reservoir of [[ammonia]] solution.<ref name=Fortes>Fortes, A. B. "[http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-45FC0TP-26&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=aa73d6642eb13527397bbec9ff9ca535 Exobiological Implications of a Possible Water-Ammonia Ocean Inside Titan]." ''Icarus'', 146(2):444-452, August 2000. Accessed February 16, 2008. [http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6WGF-45FC0TP-26-1&_cdi=6821&_user=10&_orig=search&_coverDate=08%2F31%2F2000&_sk=998539997&view=c&wchp=dGLbVlb-zSkWz&md5=644f3640a5d78afc50f8e4e50a4a09d2&ie=/sdarticle.pdf Full text] available to subscribers or for a fee.</ref> That particular model depended on the methane and the cyanide being biogenic, but as has been noted above, the methane certainly is ''not'' biogenic. The ammonia-water "[[aquifer]]" might yet exist, however, if the <sup>40</sup>Ar findings are a reliable indicator.<ref name=HuygensFindings/>
== Observation and Exploration ==
In the 300-plus years since its discovery, the only study of Titan was by observation with Earth-based telescopes. [[Pioneer 11]] made a brief flyby of Saturn in 1979 and took several low-quality images. [[Voyager 1]] and [[Voyager 2]] were next to visit Saturn in 1980 and 1981; Voyager 1 did make a close flyby of Titan, but its instruments could not penetrate the thick haze of the Titanian atmosphere.<ref name=solarviews/>
In 1994 the [[Hubble Space Telescope]] took photographs of an apparent "continent" on the Saturnian face of Titan.<ref name=nasa2/>
The first truly comprehensive study of that system is the [[Cassini-Huygens mission]], which launched on October 15, 2007 and arrived in the Saturnian system on July 1, 2004.<ref name=solarviews/> The major innovation of this mission was the use of radar equipment aboard the orbiter and the lander, to penetrate the haze.
Huygens was designed to land, and to study the atmosphere and the surface in detail on the way down. Huygens landed fully functional on Titan on January 14, 2005. It remained functional for three hours while it sent back many images and much data on the composition, including the carbon-isotopic ratio, of the Titanian atmosphere.
== Gallery ==
<gallery>
Image:Titan Saturn transit 2007.jpg|Titan transits Saturn just south of the ring plane
Image:Titan haze 2007.jpg|Titan's hazy atmosphere in ultraviolet light
Image:Titan mosaics 2006.jpg|Three false-color mosaics of Titan showing changes in its atmosphere within three months
Image:Titan surface approach 1.jpg|Surface of Titan from 17 to 8 km up, from Huygens lander as it descended
Image:Titan surface approach 2.jpg|Surface of Titan from 7 to 0.5 km up, from Huygens lander as it descended
Image:Titan landing.jpg|Surface of Titan, from Huygens lander after it landed
Image:Titan landing color.jpg|Surface of Titan, in color, from Huygens lander
</gallery>
== References ==
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