By Sabine Stanley, Ph.D., Johns Hopkins University
Saturn has at least 62 moons, seven of which are called the ‘major moons’. The largest Saturnian moon is Titan, only a little smaller than the largest moon in the solar system, and the smallest moon is tiny enough to fit in Saturn’s thin rings. It seems like the only thing these moons share is orbiting Saturn, and each is a different world, waiting to be explored.
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Saturn’s magnificent rings owe their existence to the 62 moons of the planet, not only the close moons but also the ones orbiting much farther than the rings. Saturn’s largest moon is Titan, with lakes, a subsurface ocean, and a dense, nitrogen-rich atmosphere.
In the 17th century, Christiaan Huygens discovered Titan. In the 18th century, six more Saturnian moons were discovered and named after titans or giants in Greek mythology. These seven moons are big enough to be spherical and, hence, are called the major moons. The naming pattern changed after the moons outnumbered the titans, and Norse characters, Inuit names, and Gallic names were also used.
Learn more about Saturn and the rings: Gravity’s masterpiece.
The Moons’ Orbital Properties
Almost all moons of Saturn can be grouped, based on their orbital properties and physical characteristics. There is a big group of retrograde Saturnian moons, a small group of prograde moons with orbital inclinations over 40°, and another small group with orbital inclinations about 35°.
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The seven main moons are all regular, with almost circular orbits, moving in the same prograde direction as Saturn’s rotation. The irregular moons, on the other hand, have diverse orbits, which shows that they were probably attracted to the planet. Saturnian moons can be compared to Jupiter’s moons in some aspects.
This is a transcript from the video series A Field Guide to the Planets. Watch it now, on Wondrium.
Moons of Saturn and Jupiter
Jupiter has four spherical moons, while Saturn has seven. Saturn’s four round moons, i.e., Mimas, Enceladus, Tethys, and Dione, orbit quite close to the planet, closer than Jupiter’s closest round moon. However, only two of the major moons—Rhea and Titan—are within the orbit distances of Jupiter’s four Galilean moons.
Titan is Saturn’s largest moon, and Ganymede is Jupiter’s largest. The two moons have a lot in common, from diameters to building blocks. Titan is the only Saturnian moon similar to the Galilean moons. Saturn’s second-largest moon is about 3.5 times smaller than Titan, and the smallest round moon, Mimas, has a diameter of under 400 kilometers. Still, Saturn’s moons have things in common.
Ice in Saturn’s Moons
All moons of Saturn have much ice, made of water, ammonia, and methane. Saturnian moons are all less dense than Titan, with an average density of 1880 kilograms per cubic meter. Tethys is another major moon whose density is lower than frozen water, with only 984 kilograms per cubic meter! Saturnian moons have a lot of empty pores, and Titan makes up 96% of the mass of all the moons and rings orbiting Saturn.
Titan, the Unique Moon
Titan is also the only moon in the solar system with a substantial atmosphere of around 98% nitrogen and 2% methane. Its atmospheric pressure at the surface is 1.5 bars, with an atmosphere of about 20% more massive than Earth’s and four times as dense, and a surface temperature of 94 Kelvin. The temperature is cold enough for liquid methane.
Titan’s gravity is only 14% of the Earth’s, but its atmosphere extends much higher: the mesosphere about 600 kilometers and the thermosphere up to 1200 kilometers. Conditions for flying are very appropriate on Titan, ignoring the significantly-below-freezing temperature of –300° Fahrenheit.
As mentioned before, Saturn’s Titan has many similarities with Jupiter’s Ganymede. They have a similar size and density and are made of similar material. However, their atmospheres are diversely different, due to two reasons.
Firstly, Titan is twice as far from the Sun and its radiation. Thus, it could trap more methane and nitrogen than Ganymede because of the cold temperature, and it could keep the trapped material.
Secondly, Jupiter’s gravity is much stronger than Saturn’s. Consequently, comets that hit Jupiter’s moons have higher impact speeds and more energy when hitting the surface. They could affect the atmosphere stronger than the comets hitting Saturn’s moons.
Each Saturnian moon is unique and worth exploring. No wonder, the science fiction writers have ventured to these worlds often.
Learn more about near-Earth asteroids and the asteroid belt.
Common Questions about Moons of Saturn
Moons of Saturn were initially named after titans or giants in Greek mythology, but then they outnumbered the titans. Thus, scientists used Norse, Inuit, and Gallic names for the newer moons, while the seven major moons are all named after titans.
Moons of Saturn are so far 62, with different sizes and orbital inclinations. However, the seven bigger moons were discovered around the 17th and 18th centuries and named after titans in Greek mythology. These moons are called the major moons.
No. Titan is the largest moon of Saturn and the second-largest moon in the solar system. Jupiter’s Ganymede is the largest moon in the solar system, even though it is only a little larger than Titan.
