Iapetus is a large saturnian moon, the third largest of the 62 known moons orbiting the gas giant. It is also one of the most heavily cratered and oldest surfaces in the solar system. Iapetus was discovered in 1671 by Giovanni Domenico Cassini. The moon’s most striking feature is a broad equatorial band 3,400 kilometers long and up to 1,000 kilometers wide which is two-tone (one side lighter than the other) in color. This dark material has been shown to be related to Phoebe, another saturnian satellite. Iapetus has an average diameter of 1,471 kilometers making it slightly smaller than Mercury. Its mass however is only about one eighth that of Mercury. Iapetus orbits Saturn at a distance of 3.6 million kilometers taking 79 days to complete one orbit around the planet.
The origin of Iapetus’ unusual two-tone coloring remains unknown though several theories have been proposed. One possibility is that an ancient collision created a debris field which eventually coalesced into Iapetus and Phoebe billions of years ago. Another theory suggests that dark material from Phoebe may have been deposited onto Iapetus via an electrostatic interaction called The Poynting–Robertson Effect. A third possibility posits that hydrothermal vents on the sea floor could have spewed out minerals which then coated Iapetus’ surface over time through a process known as seafloor vent deposition .
Despite its small size, Iapetus has an interesting geology with several features worthy of note. One such feature are scarps or cliffs up to 20 kilometers high which crisscross the entire surface of the moon . These scarps are thought to be caused by tidal forces as Saturn’s gravity pulls on the unevenly shaped body causing it to deform slightly over time . This deformity results in fractures along weak spots in the crust which eventually become cliffs as they slowly rise higher due to continued deformation .
Another notable geological feature on Iapetus are impact craters . As with any other heavenly body in our solar system , iapedus was bombarded by comets and asteroids throughout its history leaving behind countless impact craters dotting its surface . However , what makes these craters unique is their size and distribution . Unlike Earth where impacts tend to be scattered randomly , almost all of iapedus’ large impact basins (>100 km diameter) are clustered near its south pole . It’s thought that this dichotomy between Earth and Io resulted from different formation histories ; Earth accreted gradually over time while Io (and thus also iapedus ) assembled much more quickly due largely to Jupiter ‘s massive gravity well .