Editing Iapetus (moon) (section)

=== Equatorial ridge ===
{{Main|Equatorial ridge on Iapetus}}
[[File:Iapetus equatorial ridge.jpg|right|thumb|200px|Closeup of the equatorial ridge]]
A further mystery of Iapetus is the [[equatorial ridge]] that runs along the center of Cassini Regio, about {{cvt|1300|km||}} long, {{cvt|20|km||}} wide, and {{cvt|13|km||}} high. It was discovered when the ''Cassini'' spacecraft imaged Iapetus on December 31, 2004, although its existence had been inferred from the moon's polar images by Voyager 2.<ref>{{cite web | url=https://www.planetary.org/articles/1151 | title=Iapetus' "Voyager Mountains" }}</ref> Peaks in the ridge rise more than {{cvt|20|km||}} above the surrounding plains, making them some of the [[tallest mountains in the Solar System]]. The ridge forms a complex system including isolated peaks, segments of more than {{cvt|200|km||}} and sections with three near parallel ridges.<ref name="porco2005">{{cite journal| last=Porco | first=C. C. | author-link = Carolyn Porco | author2=E. Baker, J. Barbara, K. Beurle, A. Brahic, J. A. Burns, S. Charnoz, N. Cooper, D. D. Dawson, A. D. Del Genio, T. Denk, L. Dones, U. Dyudina, M. W. Evans, B. Giese, K. Grazier, P. Helfenstein, A. P. Ingersoll, R. A. Jacobson, T. V. Johnson, A. McEwen, [[Carl D. Murray|C. D. Murray]], G. Neukum, W. M. Owen, J. Perry, T. Roatsch, J. Spitale, S. Squyres, P. C. Thomas, M. Tiscareno, E. Turtle, A. R. Vasavada, J. Veverka, R. Wagner, R. West| date=2005-02-25
| title=Cassini imaging science: Initial results on Phoebe and Iapetus| journal=Science| volume=307| issue=5713| pages=1237–1242| pmid=15731440| doi=10.1126/science.1107981| id=2005Sci...307.1237P|bibcode = 2005Sci...307.1237P | s2cid=20749556 | url=https://authors.library.caltech.edu/36635/7/Porco_Iapetus_SOM.pdf}}</ref> Within the bright regions there is no ridge, but there are a series of isolated {{cvt|10|km||}} peaks along the equator.<ref>{{cite web |url=http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=2760 |title=Cassini–Huygens: Multimedia-Images |publisher=Saturn.jpl.nasa.gov |access-date=2012-07-30 |archive-url=https://web.archive.org/web/20110610025306/http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=2760 |archive-date=2011-06-10 |url-status=dead }}</ref> The ridge system is heavily cratered, indicating that it is ancient. The prominent [[equatorial bulge]] gives Iapetus a [[Walnut#Nuts and kernels|walnut]]-like appearance.

[[File:Iapetus_Voyager2_flyby_sequence.jpg|thumb|upright=4|center|A series of images of Iapetus's north pole taken by Voyager 2 as it flew by. The white dots at the lower part of the images (Iapetus's equator) hinted at the presence of high mountains there which will later turn out to be the equatorial bulge and duly named Voyager Mountains.]]

It is not clear how the ridge formed. One difficulty is to explain why it follows the equator almost perfectly. There are many hypotheses, but none explain why the ridge is confined to Cassini Regio. Theories include that the ridge is a remnant of Iapetus's oblate shape during its early life, that it was created by the collapse of a ring system, that it was formed by icy material welling from Iapetus's interior, or that it is a result of convective overturn.<ref>
*{{cite journal| last=Kerr| first=Richard A.
| date=2006-01-06| title=How Saturn's Icy Moons Get a (Geologic) Life| journal=Science| volume=311| issue=5757| page=29| doi=10.1126/science.311.5757.29| pmid=16400121| s2cid=28074320| doi-access=free}}
*{{Cite journal|last=|first=|date=January 21, 2005|title=Ring around a moon|url=https://www.science.org/doi/10.1126/science.307.5708.349c|journal=Science|volume=307|issue=5708|pages=349|doi=10.1126/science.307.5708.349c|s2cid=210274907|via=}}
*{{cite journal | last1 = Ip | first1 = W.-H | year = 2006 | title = On a ring origin of the equatorial ridge of Iapetus | journal = Geophysical Research Letters | volume = 33 | issue = 16| page = L16203 | doi = 10.1029/2005GL025386 | bibcode=2006GeoRL..3316203I| doi-access = free }}
*{{cite journal|url=https://www.sciencedirect.com/science/article/abs/pii/S0019103511002041|title=Ridge formation and de-spinning of Iapetus via an impact-generated satellite|journal=[[Icarus (journal)|Icarus]]|last1=Levison|first1=Harold F.|author-link=Harold F. Levison|last2=Walsh|first2=Kevin J.|last3=Barr|first3=Amy C.|last4=Dones|first4=Luke|date=August 2011|volume=214|issue=2|pages=773–778|doi=10.1016/j.icarus.2011.05.031|publisher=[[Elsevier]]|arxiv=1105.1685 |bibcode=2011Icar..214..773L |s2cid=5849043 }}
*{{cite journal| last=Czechowski | first=L. |author2=J.Leliwa-Kopystynski| date=2013-09-25| title= Remarks on the Iapetus' bulge and ridge | journal=Earth, Planets and Space| volume=65| issue=8 | pages=929–934 | doi=10.5047/eps.2012.12.008|bibcode = 2013EP&S...65..929C | doi-access=free| url=http://meetingorganizer.copernicus.org/EPSC2012/EPSC2012-834.pdf |archive-url=https://web.archive.org/web/20150109095658/http://meetingorganizer.copernicus.org/EPSC2012/EPSC2012-834.pdf |archive-date=2015-01-09 |url-status=live}}</ref>