Iapetus is Saturn’s third-largest moon, with a two-tone coloring of black and white, a huge equatorial ridge, and a very eccentric orbit. It was observed by the Cassini space probe in 2007 and is the only major moon from which Saturn’s rings are clearly visible.
Iapetus is Saturn’s third-largest moon, after Titan, which is larger than the Moon, and Rhea, which is slightly larger than Iapetus. Iapetus is slightly smaller than our Moon, with a diameter of about 1,500 km, compared to the Moon’s 1,737 km.
Iapetus has a number of physical quirks that make it a bit more interesting than any typical rocky moon. The first, and most striking, is a dramatic two-tone coloring of black and white, which has given it the nickname “the Yin-Yang moon”. Like many moons, Iapetus is tidally locked on its planet, meaning the same side always faces it. In the direction of its motion around Saturn, Iapetus is dark as coal, on the back side, bright as snow. This caused some confusion for the first astronomers who observed it, who saw the moon flicker in and out of existence as its dark and white sides wobbled from our viewpoint.
But Iapetus’ two-toned appearance isn’t the only unusual thing about it. Closer observations of the Cassini orbit have found that it has a huge equatorial ridge that follows its equator almost perfectly. With an average height of 13 km, it extends for over 200 km, with peaks in part at 20 km. In light of the fact that the highest peaks on the Moon are only about 7 km, and exist only in isolated spiers or small ridges like on Earth, Iapetus’ equatorial ridge is quite bizarre. There are various theories about its origin, none of them confirmed. Some conspiracy theorists have even taken it as proof that Iapetus is artificial!
Iapetus was closely observed by the Cassini space probe on September 10, 2007, flying about 1,640 km (1,000 mi) from its surface and taking spectacular high-resolution images of features such as the equatorial ridge and the interface between its clear and dark.
Iapetus is one of Saturn’s outer satellites, which is unusual because it is so large. Other large satellites are found much closer to the planet. Iapetus also has a very eccentric orbit, traveling far above and below Saturn’s rings as it makes its way around the planet. For this reason Iapetus is the only major moon from which Saturn’s rings would be clearly visible. The other moons orbit together with the ring particles, which means that the rings are seen edge-on and are not very pronounced. Because of its splendid view, we can safely say that Iapetus will become prime real estate in the late 21st or early 22nd century. Start saving!
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