Saturn is best known for its fabulous ring system, but it also has an amazing moon system.
Cassini and Huygens observed Saturn in the 17th century and again in the 21st century.
Jean Dominique Cassini (1625-1712) was the director of the Paris Observatory. His many achievements included the discovery of four of Saturn's moons. His contemporary Christiaan Huygens (1629-1695) discovered Saturn's moon Titan.
NASA and ESA (European Space Agency) launched the Cassini-Huygens mission to Saturn in 1997. Huygens was a probe that landed on Saturn's moon Titan. These images were taken by Huygens during its descent to the moon. The Cassini mission ended in September 2017 after more than 13 years studying the Saturnian system.
Saturn has at least 62 moons.
When Cassini-Huygens left Earth in 1997, we knew of only eighteen Saturnian moons, but there were 62 known at the end of 2010. It was quite a productive decade and a half, though only some of the moons were discovered by the Cassini probe. Ground-based telescopes discovered most of them.
Titan is the second largest moon in the Solar System and vastly bigger than all of the rest of Saturn's moons put together.
Think of the total mass of Saturn's moons. Titan's mass is 96% of it. The six comparatively large moons – Mimas, Enceladus, Tethys, Dione, Rhea and Iapetus – account for most of the remaining mass. The other 53 moons total 0.04% of it.
Titan is the most Earthlike body in the Solar System.
Titan has a thick nitrogen atmosphere rich in organic chemicals. Scientists think that it may be a cold version of ancient Earth. Even today our atmosphere is almost 80% nitrogen, and on the ancient Earth, it would have been almost all nitrogen. Oxygen entered our atmosphere in quantity after photosynthesizing organisms evolved. [To learn more about Titan, click on the link below this article.]
Mimas is the smallest known round body in the Solar System.
Any body with enough mass will collapse under its own gravity into a spheroid. Asteroids have irregular shapes because they're too small to do this. Less mass is needed for icy bodies to collapse than for rocky bodies, but it's not certain exactly where the cut-off is. Saturn's moon Mimas (pronounced MY-mass) is about 400 km (250 miles) across, and it's the smallest spherical body that we know of.
Iapetus is a two-tone moon, with one hemisphere ten times brighter than the other.
Iapetus is the most massive known body that is not spherical. It's shaped like a walnut. In this picture of Iapetus (ee-AP-e-tus) you can see the shape, and that it seems to be in shadow on the right hand side. There's no shadow. That hemisphere is as dark as coal. The dark side, which is the leading side as Iapetus obits, is fairly smooth, showing that new material has been deposited and covered old cratering. The dark material is dust from a ring created by material from an outer moon – Iapetus orbits through this debris.
Some of Saturn's rings have "shepherd" moons.
Shepherds herd sheep and shepherd moons herd rings! Some small moons orbit just to one side of a ring, and their gravitational influence helps define the ring shape and maintain the gaps between them. Here are Prometheus and Pandora shepherding Saturn's F rings.
Hyperion is not tidally locked to Saturn.
On Earth we always see the same side of the Moon, because it's tidally locked to Earth. Therefore it takes just as long to rotate on its axis as it does to orbit the Earth. This is the result of gravitational interaction of a moon and its planet, and is common throughout the Solar System (and beyond). Saturn's spongy-looking moon Hyperion (hi-PEER-ee-un) is the notable exception, because the gravity of nearby Titan causes its motion to be unpredictable.
Enceladus is geologically active and could harbor life.
Enceladus (en-SELL-uh-dus) is one of the few Solar System bodies which have been seen erupting. There's evidence of a large ocean under the moon's surface. In part at least, it remains liquid because of the heat generated by the tidal stresses caused by Jupiter's gravity. Despite its frozen surface and great distance from the Sun, Enceladus has three essential ingredients for life to form – heat, organic material, and water. [To learn more about Enceladus, click on the link below this article.]
None of Saturn's moons was given a name until the nineteenth century.
To Huygens, Titan was "Saturn's moon", and Cassini referred to his four discoveries as "Louis's stars" in honor of his patron King Louis XVI. Other astronomers simply gave the moons numbers, based on their order outward from Saturn. That got quite confusing as more moons were discovered, and in 1847 John Herschel suggested names from the mythology of Saturn (Cronos in Greek). Cronos was a Titan, one of the children of Uranus and Gaia. Herschel named the large moon Titan, and gave the others names of Titans. Since there were only a limited number of Titans, other mythologies (Inuit, Norse, Celtic) have been used for the newer discoveries.