Equatorial ridge
Iapetus's equatorial ridge up close as imaged by Cassini
Feature typeMountains
Coordinates0°N 0°W / 0°N -0°E / 0; -0
Length1,300 km (810 mi)
Peak20 km (12 mi)

The equatorial ridge is the tallest mountain feature on Saturn's moon Iapetus. It is 20 km (12 mi) high, and is the third tallest mountain structure in the Solar System. It runs along most of Iapetus' equator. It was discovered by the Cassini probe in 2004. The ridge's origin is unknown. There are bright areas on the sides of the equatorial ridge near Iapetus' bright trailing hemisphere, which were already visible in Voyager 2 images appearing like mountains and were nicknamed the "Voyager Mountains".[1]


Iapetus's equatorial ridge was discovered when the Cassini spacecraft imaged Iapetus on 31 December 2004. Peaks in the ridge rise more than 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 200 km and sections with three near parallel ridges.[2]


Within the bright regions there is no ridge, but there are a series of isolated 10 km peaks along the equator.[3] The ridge system is heavily cratered, indicating that it is ancient. The prominent equatorial bulge gives Iapetus a walnut-like appearance.

It is not clear how the ridge formed. One difficulty is to explain why it follows the equator almost perfectly. There are at least four current hypotheses, but none of them explains why the ridge is confined to Cassini Regio.


See also


  1. ^ Iapetus' "Voyager Mountains"
  2. ^ Porco, C. C.; 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, 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 (2005-02-25). "Cassini imaging science: Initial results on Phoebe and Iapetus". Science. 307 (5713): 1237–1242. Bibcode:2005Sci...307.1237P. doi:10.1126/science.1107981. PMID 15731440. S2CID 20749556. 2005Sci...307.1237P.((cite journal)): CS1 maint: multiple names: authors list (link)
  3. ^ "Cassini–Huygens: Multimedia-Images". Saturn.jpl.nasa.gov. Archived from the original on 2011-06-10. Retrieved 2012-07-30.
  4. ^ Kerr, Richard A. (2006-01-06). "How Saturn's Icy Moons Get a (Geologic) Life". Science. 311 (5757): 29. doi:10.1126/science.311.5757.29. PMID 16400121. S2CID 28074320.
  5. ^ "Ring around a moon?". Science. 207 (5708): 349. January 21, 2005. doi:10.1126/science.307.5708.349c. S2CID 210274907.
  6. ^ Ip, W.-H (2006). "On a ring origin of the equatorial ridge of Iapetus". Geophysical Research Letters. 33 (16): L16203. Bibcode:2006GeoRL..3316203I. doi:10.1029/2005GL025386.
  7. ^ Levison, Harold F.; Walsh, Kevin J.; Barr, Amy C.; Dones, Luke (August 2011). "Ridge formation and de-spinning of Iapetus via an impact-generated satellite". Icarus. Elsevier. 214 (2): 773–778. arXiv:1105.1685. Bibcode:2011Icar..214..773L. doi:10.1016/j.icarus.2011.05.031. S2CID 5849043.
  8. ^ Czechowski, L.; J.Leliwa-Kopystynski (2012-09-25). "Isostasy on Iapetus: the myth of fossil bulge" (PDF). EPSC Abstracts. 7: 834.
  9. ^ Czechowski, L.; J.Leliwa-Kopystynski (2013-09-25). "Remarks on the Iapetus' bulge and ridge" (PDF). Earth, Planets and Space. 65 (8): 929–934. Bibcode:2013EP&S...65..929C. doi:10.5047/eps.2012.12.008.
  10. ^ https://www.planetary.org/articles/1151
  11. ^ https://science.nasa.gov/resource/dark-stained-iapetus/
  12. ^ "Iapetus". Cassini Solstice Mission. NASA. Archived from the original on 2015-03-26. Retrieved 6 July 2015.
  13. ^ https://science.nasa.gov/resource/approaching-iapetus/