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・ Equatorial Guinean presidential election, 1973
・ Equatorial Guinean presidential election, 1989
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・ Equatorial Guinean presidential election, 2002
・ Equatorial Guinean presidential election, 2009
・ Equatorial Guinea–Nigeria Maritime Boundary Treaty
・ Equatorial Guinea–North Korea relations
・ Equatorial Guinea–Russia relations
・ Equatorial Guinea–São Tomé and Príncipe Maritime Boundary Treaty
・ Equatorial Guinea–United States relations
・ Equatorial layered deposits
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Equatorial ridge
・ Equatorial ridge on Iapetus
・ Equatorial ring
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・ Equatorial Rossby wave
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・ Equatorial saki
・ Equatorial sextant
・ Equatorial Spanish
・ Equatorial spitting cobra
・ Equatorial Vortex Experiment
・ Equatorial waves
・ Equatorium
・ Equatorius
・ Equens


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Equatorial ridge : ウィキペディア英語版
Equatorial ridge

Equatorial ridges are a feature of at least three of Saturn's moons: the large moon Iapetus and the tiny moons Atlas and Pan. They are ridges that closely follow the moons' equators. They appear to be unique to the Saturnian system, but it is uncertain whether the occurrences are related or a coincidence. All three were discovered by the ''Cassini'' probe in 2005.
The ridge on Iapetus is nearly 20 km wide, 13 km high and 1,300 km long. The ridge on Atlas is proportionally even more remarkable given the moon's much smaller size, giving it a disk-like shape. Images of Pan are less clear, but show a structure similar to that of Atlas.
It is not certain how these ridges formed, or whether there is any connection between them. Because Atlas and Pan orbit within the rings of Saturn, a likely explanation for their ridges is that they sweep up ring particles as they orbit, which build up around their equators. This theory is less applicable to Iapetus, which orbits far beyond the rings. One scientist has suggested that Iapetus swept up a ring before being somehow expelled to its current, distant orbit.〔()〕 Others think it was stationary and it is the rings that have been pulled away from it, falling into Saturn's gravity field. Perhaps more likely is the theory that because Iapetus has an unusually large Hill sphere compared to other moons in our solar system, it could once have had its own ring, or even a moonlet that was slowly pulled in closer, torn up into a ring, and then gradually accreted onto Iapetus' equator. But most scientists prefer to assume that Iapetus's ridge was produced by some kind of internal source and is unrelated to the ridges on Atlas and Pan.
==References==


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