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Saturn: Moons

Half image of Saturn and its rings with moons Tethys and Dione against the background of space.
Saturn and two of its moons, Tethys (above) and Dione
On March 24, 1655, only Earth and Jupiter were known to have moons. The next day, Christiaan Huygens added Saturn to the list when he discovered its largest moon, Titan.

Since then, we've discovered a total of 46 natural satellites orbiting Saturn. Some, like Pan, Atlas, Prometheus, and Pandora, are "shepherd moons" that herd Saturn's orbiting particles into distinct ring. Some moons produce twisting and wave patterns in the rings.

One moon, Enceladus, is one of the shiniest objects in the solar system. It's about as wide as Arizona and covered with water ice that reflects sunlight like freshly fallen snow. That makes it extremely cold, only about -201°C (-330°F). It may be that volcanoes on this moon erupted the icy particles that form Saturn's E-ring, and that they continuously snow back down onto its surface.

Mimas, only 392 km (244 miles) in diameter, has a giant crater one-third as wide as the moon, itself. And in its center is a peak about two-thirds the height of Mt. Everest, the highest point on Earth.

Iapetus is among the strangest of Saturn's moons. Half of it is ten times brighter than the other half.

Epimetheus and Janus trade orbits with each other every few years, taking turns being closer to their planet.

Phoebe may be a captured Centaur, an object that wandered sunward from its home in the Kuiper Belt, far beyond Pluto.

But it is mysterious Titan that intrigues scientists most.

Titan is the second-largest moon in the entire solar system (Jupiter's Ganymede is slightly larger). It's bigger than two planets, Mercury and Pluto. Circling Saturn far from the Sun, its surface temperature is only -180? C (-292? F). And it's the only moon with a dense atmosphere -- so dense, in fact, that Titan's near-surface atmospheric pressure is about 60% greater than Earth's. That's about what a scuba diver feels under 20 feet of water.

Close-up of Titan's orangish haze.
Titan's atmospheric haze.
Scientists think Titan's atmosphere may resemble that of Earth when life began to form here. So studying Titan might help us learn about the early days of our own planet.

We finally had a good look at Titan's surface when Europe's Huygens probe, named for the Dutch astronomer, landed on Titan January 14, 2005. (Previously, its thick deep-red haze hid it from the two Voyager spacecraft that visited in 1980 and 1981.) The probe got a ride from NASA's Cassini spacecraft, which is currently in a four-year orbital mission around Saturn.

Since the Cassini spacecraft arrived at Saturn we've been learning much more about the moons -- and we might possibly discover more.

Saturn's Moons
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