Journey Through the Solar System: Saturn

Saturn Pictures Gallery - Blinding Saturn
Surely one of the most gorgeous sights the solar system has to offer, Saturn sits enveloped by the full splendor of its stately rings. NASA/JPL/Space Science Institute

Saturn is a gas giant planet in the outer solar system best known for its beautiful ring system.  Astronomers have studied it closely using ground-based and space-based telescopes ​and found dozens of moons and fascinating views of its turbulent atmosphere. 

Seeing Saturn from Earth

Saturn looks like a disk-like bright dot in the sky (shown here in early morning for late winter 2018). Its rings can be spotted using binoculars or a telescope. Carolyn Collins Petersen

Saturn appears as a bright dot of light in the darkened sky. That makes it easily visible to the naked eye. Any astronomy magazine, desktop planetarium, or astro app can supply information about where Saturn is in the sky for observing.

Because it is so easy to spot, people have been watching Saturn since ancient times. However, it wasn't until the early 1600s and the invention of the telescope that observers could see more details. The first person to use one to take a good look was Galileo Galilei. He spotted its rings, although he thought they might be "ears." Since then, Saturn has been a favorite telescope object for professional and amateur astronomers.

Saturn by the Numbers

Saturn is so far out in the solar system it takes 29.4 Earth years to make one trip around the Sun, which means that Saturn will go around the Sun only a few times in any human's lifetime.

In contrast, Saturn's day is much shorter than Earth's. On average, Saturn takes a little over 10 and a half hours "Earth time" to spin once on its axis. Its interior moves at a different rate than its cloud deck. 

While Saturn has nearly 764 times the volume of Earth, its mass is only 95 times as great. This means that Saturn's average density is about 0.687 grams per cubic centimeter. That's significantly less than the density of water, which is 0.9982 grams per cubic centimeter.  

Saturn's size definitely puts it in the giant planet category. It measures 378,675 km around at its equator.

Saturn From the Inside

saturn interior
An artist's view of the interior of Saturn, along with its magnetic field. NASA/JPL

 Saturn is made mostly of hydrogen and helium in gaseous form. That's why it's called a "gas giant." However, the deeper layers, beneath the ammonia and methane clouds, are actually in the form of liquid hydrogen. The deepest layers are liquid metallic hydrogen ​and are where the planet's strong magnetic field is generated. Buried deep down is a small rocky core, about the size of Earth. 

Saturn's Rings Are Made Primarily of Ice and Dust Particles

Despite the fact that the rings of Saturn look like continuous hoops of matter encircling the giant planet, each one is actually made of tiny individual particles. About 93 percent of the "stuff" of the rings is water ice. Some of them are chunks as large as a modern car. However, most of the pieces are the size of dust particles.There is also some dust in the rings, which are divided by gaps that are cleared out by some of Saturn's moons.

It isn't Clear How The Rings Formed

There is a good likelihood that the rings are actually the remnants of a moon that was ripped apart by Saturn's gravity. However, some astronomers suggest that the rings formed naturally alongside the planet in the early solar system from the original solar nebula. No one is sure how long the rings will last, but if they were formed when Saturn did, then they could last quite a long time indeed.

Saturn Has At Least 62 Moons

In the inner part of the solar system, the terrestrial worlds (Mercury, Venus, Earth, and Mars) have few (or no) moons. However, the outer planets are each surrounded by dozens of moons. Many are small, and some may have been passing asteroids trapped by the planets' massive gravitational pulls. Others, though, appear to have formed out of material from the early solar system and remained trapped by the evolving giants nearby. Most of Saturn's moons are icy worlds, although Titan is a rocky surface covered with ices and a thick atmosphere.

Bringing Saturn Into Sharp Focus

Saturn Pictures Gallery - Radio Occultation: Unraveling Saturn's Rings
Specially designed Cassini orbits place Earth and Cassini on opposite sides of Saturn's rings, a geometry known as occultation. Cassini conducted the first radio occultation observation of Saturn's rings on May 3, 2005. NASA/JPL

With better telescopes came better views, and over the next several centuries we came to know a great deal about this gas giant.

Saturn's Largest Moon, Titan, Is Bigger Than the Planet Mercury

Titan is the second largest moon in our solar system, behind only Jupiter's Ganymede. Because of its gravity and gas production Titan is the only moon in the solar system with an appreciable atmosphere. It is made mostly of water and rock (in its interior), but has a surface covered with nitrogen ice and methane lakes and rivers. 

Edited by Carolyn Collins Petersen.