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	Enceladus At a Glance
	Discovery 1789, William Herschel Diameter 310 miles 500 km Distance from Saturn 147,812 miles 238,020 km Orbital Period 1.4 days Compare Moons
	Mimas At a Glance
	Discovery 1789, William Herschel Diameter 2,985 miles 4,806 km Distance from Saturn 115,210 miles 185,520 km Orbital Period 22 hours, 37 minutes Compare Moons

Enceladus, a small ball of ice and rock, is the most reflective surface in the solar system: it reflects 99 percent of the visible sunlight that strikes it back into space. Cassini discovered that Enceladus has a tenuous atmosphere, which is resupplied by water vapor and water ice leaking from parallel cracks in the crust near its south pole (shown in blue in this color-enhanced Cassini image, right).

Most of this material falls back onto the surface as clean ice, which is highly reflective. In essence, Enceladus re-polishes its surface with material from its interior. Because of the moon's weak gravity, however, much of the material escapes Enceladus and supplies fresh ice to Saturn's outermost ring.

Iapetus At a Glance
Discovery 1671, Jean Dominique Cassini Diameter 893 miles 1,436 km Distance from Saturn 2.2 million miles 3.6 million km Orbital Period 79.3 days Compare Moons

Iapetus
One side of Iapetus is as bright as snow, while the other is almost as dark as charcoal (left). The leading hemisphere may pick up particles of dark material that are blasted off the surface of another moon by impacts with meteorites, or the material may be ice that bubbled up from below the surface and was darkened by exposure to radiation. A ridge up to eight miles (13 km) high circles the equator, making Iapetus look a bit like a walnut. There is no clear explanation for what created the ridge.

Mimas
Mimas is nicknamed the "Death Star Moon" because a circular crater about one-third of the moon's diameter makes it resemble the big battle stations from the "Star Wars" movies. The crater (top center, above) formed when an asteroid or comet slammed into Mimas. The impact was so powerful that it almost blasted the moon to bits. Had the collision been just a little more powerful, it would have pulverized Mimas, forming a new ring around Saturn. Instead, Mimas appears to sweep out a wide gap in the rings, as some of the ring particles march in step with the Death Star Moon.

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