Changes

== Atmosphere ==

== 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 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>

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>

Before the launch of the [[Cassini-Huygens Mission]] (see below), speculations 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/>

Before the launch of the [[Cassini-Huygens Mission]] (see below), speculations 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 ¹³C methane—not the ¹²C 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>

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 ¹³C methane—not the ¹²C 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. {{doi|10.1006/icar.2000.6400}} 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.

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. {{doi|10.1006/icar.2000.6400}} 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.

== In fiction ==

== In fiction ==

Titan was a frequent staple of [[science fiction]] in the 1950's and 1960's. Specifically:

Titan was a frequent staple of [[science fiction]] in the 1950s and 1960s. Specifically:

*[[Robert A. Heinlein]] conceived of Titan as an ideal location for a cold-regions field-testing laboratory for emergency survival equipment.

*[[Robert A. Heinlein]] conceived of Titan as an ideal location for a cold-regions field-testing laboratory for emergency survival equipment.

*[[Carey Rockwell]] conceived of Titan as a mining colony. He never made clear exactly what sort of mineral wealth Titan might possess, but the hydrocarbons alone (and in a reducing atmosphere) might have been a good candidate, had Mr. Rockwell known then what [[NASA]] and the [[ESA]] know today.

*[[Carey Rockwell]] conceived of Titan as a mining colony. He never made clear exactly what sort of mineral wealth Titan might possess, but the hydrocarbons alone (and in a reducing atmosphere) might have been a good candidate, had Mr. Rockwell known then what NASA and the [[ESA]] know today.

*[[Larry Niven]] envisioned Titan as an exclusive and expensive resort destination. He conceived of a resort built on Titan's Saturnine face, where guests could gaze at Saturn and its rings. He wrote this concept, of course, ''before'' [[Voyager 1]] made its flyby and was unable to photograph the surface of Titan through the haze. Moreover, Titan's orbit is only slightly inclined with respect to the ring plane, so that even had the atmosphere been clear, the view might not have been as spectacular as Mr. Niven might have imagined.

*[[Larry Niven]] envisioned Titan as an exclusive and expensive resort destination. He conceived of a resort built on Titan's Saturnine face, where guests could gaze at Saturn and its rings. He wrote this concept, of course, ''before'' [[Voyager 1]] made its flyby and was unable to photograph the surface of Titan through the haze. Moreover, Titan's orbit is only slightly inclined with respect to the ring plane, so that even had the atmosphere been clear, the view might not have been as spectacular as Mr. Niven might have imagined.