Changes

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/>

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/>

Magnetometric experiments have not shown any appreciable [[magnetic dipole moment]] on Titan at present.<ref name=Backes>Backes, Heiko, Neubauer, Fritz M., Dougherty, Michele K., ''et al''. "[http://www.sciencemag.org/cgi/content/abstract/308/5724/992 Titan's Magnetic Field Signature During the First Cassini Encounter]." ''Science'', 308(5724):992-995, May 13, 2005. <doi:10.1126/science.1109763> Accessed May 16, 2008.</ref>

Magnetometric experiments have not shown any appreciable [[magnetic dipole moment]] on Titan at present.<ref name=Backes>Backes, Heiko, Neubauer, Fritz M., Dougherty, Michele K., ''et al''. "[http://www.sciencemag.org/cgi/content/abstract/308/5724/992 Titan's Magnetic Field Signature During the First Cassini Encounter]." ''Science'', 308(5724):992-995, May 13, 2005. {{doi|10.1126/science.1109763}} Accessed May 16, 2008.</ref>

== Atmosphere ==

== Atmosphere ==

== Liquid Hydrocarbons on Titan ==

== Liquid Hydrocarbons on Titan ==

Until the Cassini spacecraft arrived at Saturn, most astronomers understood that Titan's atmosphere had methane as a significant component, and speculated that this methane must derive from a surface ocean of methane. Yet initial observations of Titan's south pole disclosed no such ocean,<ref name=physorg>"[http://www.physorg.com/news5626.html No oceans on Titan, say researchers]." <http://physorg.com/>, August 4, 2005. Accessesd May 16, 2008.</ref> and indeed not more than two small lakes.<ref name=esach>"[http://www.esa.int/esaSC/SEMCSUUHJCF_index_0.html Titan's surface organics surpass oil reserves on Earth]." [[European Space Agency]], February 13, 2008. Accessed May 16, 2008.</ref> But observations of the north pole revealed vast liquid hydrocarbon deposits in the form of multiple lakes and streams, rather than a world-covering ocean.<ref name=esach/><ref name=Lorenz>Lorenz, Ralph D., Mitchell, Karl L., Kirk, Randolph L., ''et al''. "[http://www.agu.org/pubs/crossref/2008/2007GL032118.shtml Titan's inventory of organic surface materials]." ''Geophysical Research Letters'', vol. 35, L02206, January 29, 2008. <doi:10.1029/2007GL032118> Accessed May 16, 2008.</ref> These findings easily surpass all the known hydrocarbon reserves on Earth. Yet Lorenz ''et al.'' note that while the liquid lakes appear adequate in the short term to replenish methane lost through photolysis, they could ''not'' keep the atmosphere supplied with methane over [[deep time]].

Until the Cassini spacecraft arrived at Saturn, most astronomers understood that Titan's atmosphere had methane as a significant component, and speculated that this methane must derive from a surface ocean of methane. Yet initial observations of Titan's south pole disclosed no such ocean,<ref name=physorg>"[http://www.physorg.com/news5626.html No oceans on Titan, say researchers]." <http://physorg.com/>, August 4, 2005. Accessesd May 16, 2008.</ref> and indeed not more than two small lakes.<ref name=esach>"[http://www.esa.int/esaSC/SEMCSUUHJCF_index_0.html Titan's surface organics surpass oil reserves on Earth]." [[European Space Agency]], February 13, 2008. Accessed May 16, 2008.</ref> But observations of the north pole revealed vast liquid hydrocarbon deposits in the form of multiple lakes and streams, rather than a world-covering ocean.<ref name=esach/><ref name=Lorenz>Lorenz, Ralph D., Mitchell, Karl L., Kirk, Randolph L., ''et al''. "[http://www.agu.org/pubs/crossref/2008/2007GL032118.shtml Titan's inventory of organic surface materials]." ''Geophysical Research Letters'', vol. 35, L02206, January 29, 2008. {{doi|10.1029/2007GL032118}} Accessed May 16, 2008.</ref> These findings easily surpass all the known hydrocarbon reserves on Earth. Yet Lorenz ''et al.'' note that while the liquid lakes appear adequate in the short term to replenish methane lost through photolysis, they could ''not'' keep the atmosphere supplied with methane over [[deep time]].

== The Prebiotic-Abiotic Controversy ==

== The Prebiotic-Abiotic Controversy ==