On March 24, 1655, only Earth
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
, and Pandora
, are "shepherd
moons" that herd Saturn's orbiting particles into distinct ring
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.
, 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.
is among the strangest of Saturn's moons. Half of it is ten
times brighter than the other half.
trade orbits with each other every few years,
taking turns being closer to their planet.
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
is slightly larger). It's bigger than two planets, Mercury
. 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
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.