**3.3 Iapetus**

Iapetus is one of the most distant large moons from Saturn, and its radius is 712 km. Its gravity level is 2.4 × 10<sup>−</sup><sup>2</sup> of Earth's gravity. This moon has a ridge that girdles a significant fraction of the equator. One hemisphere has very dark material, with an albedo is 2–6%, while the other hemisphere in comparison is very bright. The composition of the dark material is perhaps organic material and carbon. Simulations have suggested that the dark materials may have been deposited by numerous particle collisions. An alternative theory is that magma from the interior has risen to the surface and that magma may be visible in photos as materials that have filled in numerous craters.
