Iapetus — Saturn’s Double-Sided Moon

Description:

Iapetus has two distinctly different sides. The leading hemisphere is dark with an albedo (reflectivity) of .04, almost the same as asphalt. In contrast, the trailing side is bright with an albedo of .6, almost the same as snow. The dark region is called the Cassini Regio and the bright region is Roncevaux Terra. The reason for this difference in coloration is still unknown, though there are two main hypotheses. The first is that the moon has accumulated dust from other moons around Saturn as it travels along its orbit. The other theory is that the dark material erupted onto Iapetus from the core. The edge between the dark and light region is not a sharp edge, as originally thought, but soft, with some craters lined with the dark material on one side but not the other. The dark material is superimposed over the topography, which leads scientists to believe that the coating is relatively young.

Iapetus touts not only a unique coloration, but also a ridge that follows almost exactly along the equator of the moon in the Cassini Regio. This ridge, discovered on December 31, 2004, is 8 miles higher than the surrounding land and runs over 800 miles. Reasons for the existence of this ridge are unknown, but many varying theories do exist. Iapetus is also a heavily cratered moon containing three craters with diameters greater than 200 miles. The largest of these has a diameter of over 300 miles wide with cliffs that drop over 9 miles.

Notable Features:

Roncevaux Terra: bright region
Cassini Regio: dark region
Ridge along the equator
Several craters with diameters over 200 miles

Data Category

Major: Astronomy
Minor: Saturn

Keywords:

Solar System, moon

Data Set Name	iapetus
Data Set Source	Cassini and Voyager Image details
Data Set Developer	NASA/JPL/ Space Science Institute Steve Albers, NOAA/GSD Ted Stryk
Visualization Developer	Steve Albers, NOAA/GSD
Audio	No
Download	FTP