Editing Titan (moon) (section)

== Bulk characteristics ==
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 | image1    = Titan, Earth & Moon size comparison.jpg
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 | caption1  = Size comparison: Titan (''lower left'') with the Moon and Earth (''top and right'')
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 | caption2  = A model of Titan's internal structure showing [[ice-six]] layer
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Titan is 5,149.46 km (3,199.73 mi) in diameter;<ref name="Zebker 2018" /> it is 6% larger than the planet [[Mercury (planet)|Mercury]] and 50% larger than Earth's [[Moon]].<ref name="s397">{{cite book | last1=Lorenz | first1=Ralph | last2=Mitton | first2=Jacqueline | title=Titan Unveiled | publisher=[[Princeton University Press]] | date=2010 | isbn=978-1-4008-3475-4 | page=1}}</ref> Titan is the tenth-largest object known in the Solar system, including the [[Sun]].<ref name="r979">{{cite book | last=Seargent | first=David A. J. | title=Weird Worlds | publisher=Springer Science & Business Media | publication-place=New York | date=2013 | isbn=978-1-4614-7064-9 | page=175}}</ref> Before the arrival of ''[[Voyager 1]]'' in 1980, Titan was thought to be slightly larger than [[Ganymede (moon)|Ganymede]],<ref name="n251"/> which has a diameter 5,262 km (3,270 mi), and thus the largest moon in the Solar System.<ref name="t309">{{cite web | title=Ganymede | website=Welcome to the NSSDCA | date=March 29, 1998 | url=https://nssdc.gsfc.nasa.gov/imgcat/html/object_page/gal_mrps94229.html | access-date=July 27, 2024}}</ref><ref name="v464">{{cite book | last=Angelo | first=Joseph A. | title=Encyclopedia of Space and Astronomy | publisher=Infobase Publishing | date=2014 | isbn=978-1-4381-1018-9 | page=258}}</ref><ref name="v466">{{cite book | last=Raina | first=Nater Singh | title=Contemporary Physical Geography | publisher=Concept Publishing Company | publication-place=New Delhi | date=2012 | isbn=978-81-8069-761-6 | page=38}}</ref> This was an overestimation caused by Titan's dense, opaque atmosphere, with a haze layer 100–200 km above its surface. This increases its apparent diameter.<ref name="nineplanets">{{cite web |last=Arnett |first=Bill |date=2005 |url=https://seds.lpl.arizona.edu/nineplanets/nineplanets/titan.html |title=Titan |publisher=University of Arizona, Tucson |work=Nine planets |access-date=April 10, 2005 |archive-url=https://web.archive.org/web/20051121130738/https://seds.lpl.arizona.edu/nineplanets/nineplanets/titan.html |archive-date=November 21, 2005 |url-status=dead }}</ref> Titan's diameter and mass (and thus its density) are similar to those of the Jovian moons Ganymede and [[Callisto (moon)|Callisto]].<ref name="LunineAstro">{{cite web |last=Lunine |first=Jonathan I. |url=https://www.astrobio.net/index.php?option=com_retrospection&task=detail&id=1493/ |title=Comparing the Triad of Great Moons |work=Astrobiology Magazine |date=March 21, 2005 |access-date=July 20, 2006 |url-status=dead |archive-url=https://web.archive.org/web/20190707213259/https://www.astrobio.net/index.php?option=com_retrospection&task=detail&id=1493%2F |archive-date=July 7, 2019 }}</ref> Based on its bulk density of 1.881&nbsp;g/cm<sup>3</sup>, Titan's composition is 40–60% rock, with the rest being water ice and other materials.<ref name="TitanfromCH">{{cite book |editor-last1=Brown |editor-first1=R. H. |editor-last2=Lebreton |editor-first2=J-P |editor-last3=Waite |editor-first3=J. H. |title=Titan from Cassini-Huygens |date=October 13, 2009 |isbn=978-1-4020-9214-5 |publisher=Springer Dordrecht |doi=10.1007/978-1-4020-9215-2 |edition=1st |bibcode=2010tfch.book...35L }}</ref>{{rp|30}}

Titan is probably partially differentiated into distinct layers with a 3,400 km (2,100 mi) rocky center.<ref>{{Cite journal |last1=Mitri |first1=G. |last2=Pappalardo |first2=R. T. |last3=Stevenson |first3=D. J. |date=December 1, 2009 |title=Is Titan Partially Differentiated? |journal=AGU Fall Meeting Abstracts |volume=43 |pages=P43F–07 |bibcode=2009AGUFM.P43F..07M}}</ref> This rocky center is believed to be surrounded by several layers composed of different crystalline forms of ice, and/or water.<ref name="Tobie">{{cite journal
|last1=Tobie |first1=G. |last2=Grasset |first2=Olivier |last3=Lunine |first3=Jonathan I. |last4=Mocquet |first4=Antoine |last5=Sotin |first5=Christophe
|date=2005 |bibcode=2005Icar..175..496T
|title=Titan's internal structure inferred from a coupled thermal-orbital model |journal=Icarus
|volume=175 |issue=2 |pages=496–502
|doi=10.1016/j.icarus.2004.12.007 }}</ref> The exact structure depends heavily on the heat flux from within Titan itself, which is poorly constrained. The interior may still be hot enough for a liquid layer consisting of a "[[cryovolcano#etymology and terminology|magma]]" composed of water and [[ammonia]] between the [[Ice Ih|ice I<sub>h</sub>]] crust and deeper ice layers made of high-pressure forms of ice. The heat flow from inside Titan may even be too high for high pressure ices to form, with the outermost layers instead consisting primarily of liquid water underneath a surface crust.<ref>{{Cite journal |last1=Sohl |first1=F. |last2=Solomonidou |first2=A. |last3=Wagner |first3=F. W. |last4=Coustenis |first4=A. |last5=Hussmann |first5=H. |last6=Schulze-Makuch |first6=D. |date=May 23, 2014 |title=Structural and tidal models of Titan and inferences on cryovolcanism |journal=Journal of Geophysical Research: Planets |language=en |volume=119 |issue=5 |pages=1013–1036 |doi=10.1002/2013JE004512|doi-access=free |bibcode=2014JGRE..119.1013S }}</ref> The presence of ammonia allows water to remain liquid even at a temperature as low as {{convert|176|K|°C}} (for [[eutectic]] mixture with water).<ref name="longstaff" /> 

The ''Cassini'' probe discovered evidence for the layered structure in the form of natural [[extremely low frequency|extremely-low-frequency]] radio waves in Titan's atmosphere. Titan's surface is thought to be a poor reflector of extremely-low-frequency radio waves, so they may instead be reflecting off the liquid–ice boundary of a [[subsurface ocean]].<ref name="Titan ELF">{{cite news |url=https://www.esa.int/esaMI/Cassini-Huygens/SEM17F9RR1F_0.html |title=Titan's Mysterious Radio Wave |date=June 1, 2007 |publisher=ESA Cassini-Huygens web site |access-date=March 25, 2010 |url-status=live |archive-url=https://web.archive.org/web/20110605000409/https://www.esa.int/esaMI/Cassini-Huygens/SEM17F9RR1F_0.html |archive-date=June 5, 2011 }}</ref> Surface features were observed by the ''Cassini'' spacecraft to systematically shift by up to 30 km (19 mi) between October 2005 and May 2007, which suggests that the crust is decoupled from the interior, and provides additional evidence for an interior liquid layer.<ref name="NS2008">{{cite web |last=Shiga |first=David |date=March 20, 2008 |url=https://www.newscientist.com/article/dn13516 |title=Titan's changing spin hints at hidden ocean |work=New Scientist |url-status=live |archive-url=https://web.archive.org/web/20141021144006/https://www.newscientist.com/article/dn13516 |archive-date=October 21, 2014 }}</ref> Further supporting evidence for a liquid layer and ice shell decoupled from the solid core comes from the way the gravity field varies as Titan orbits Saturn.<ref name="Iess et al. 2012">{{Cite journal |doi=10.1126/science.1219631 |pmid=22745254 |title=The Tides of Titan |journal=Science |volume=337 |issue=6093 |pages=457–9 |year=2012 |last1=Iess |first1=L. |last2=Jacobson |first2=R. A. |last3=Ducci |first3=M. |last4=Stevenson |first4=D. J. |last5=Lunine |first5=Jonathan I. |last6=Armstrong |first6=J. W. |last7=Asmar |first7=S. W. |last8=Racioppa |first8=P. |last9=Rappaport |first9=N. J. |last10=Tortora |first10=P. |bibcode=2012Sci...337..457I |hdl=11573/477190 |s2cid=10966007 |url=https://resolver.caltech.edu/CaltechAUTHORS:20120813-090552775 |hdl-access=free }}</ref> Comparison of the gravity field with the RADAR-based topography observations<ref>{{Cite journal |doi = 10.1126/science.1168905| pmid = 19342551 |title = Size and Shape of Saturn's Moon Titan |journal = Science |volume = 324 |issue = 5929 |pages = 921–3 |year = 2009 |last1 = Zebker |first1=H. A. |last2 = Stiles |first2 = B. |last3 = Hensley |first3 = S. |last4 = Lorenz |first4 = R. |last5 = Kirk |first5=R. L. |last6=Lunine |first6=Jonathan I. |bibcode =2009Sci...324..921Z |s2cid = 23911201 |url = https://pdfs.semanticscholar.org/7ec3/29458f5dabfa6c370476df8236779941f93f.pdf |archive-url = https://web.archive.org/web/20200212021254/https://pdfs.semanticscholar.org/7ec3/29458f5dabfa6c370476df8236779941f93f.pdf |url-status = dead |archive-date = February 12, 2020}}</ref> also suggests that the ice shell may be substantially rigid.<ref name="Hemingway et al. 2013">{{Cite journal |doi = 10.1038/nature12400| pmid = 23985871 |title = A rigid and weathered ice shell on Titan |journal = Nature |volume = 500 |issue = 7464 |pages = 550–2 |year = 2013| last1 = Hemingway |first1 = D. |last2 = Nimmo |first2 = F. |last3 = Zebker |first3 = H. |last4 = Iess |first4 = L. |bibcode = 2013Natur.500..550H | hdl = 11573/563592 |s2cid = 4428328}}</ref><ref name="jpl.nasa.gov">{{cite web |url=https://www.jpl.nasa.gov/news/news.php?release=2013-261 |title=Cassini Data: Saturn Moon May Have Rigid Ice Shell |publisher=JPL |url-status=live |archive-url=https://web.archive.org/web/20141020103435/https://www.jpl.nasa.gov/news/news.php?release=2013-261 |archive-date=October 20, 2014}}</ref>