It’s Professor Dave, let’s look at Saturn.
We just looked at Jupiter and its strange moons, so now let’s look at the sixth planet
from the sun, Saturn, which turns out to be quite similar to Jupiter in a lot of ways.
Saturn is the Roman name for the Greek god Cronus, who was the father of Zeus and other
gods, so what can we say about this father of kings?
First let’s note that we are getting very far away from the sun.
While Jupiter was a little more than five astronomical units away from the sun, or five
times as far as Earth, Saturn is already almost ten astronomical units away, or almost twice
as far as Jupiter is.
It’s also very large, nearly as large as Jupiter, and even less dense, less dense than
water in fact, which means that quite incredibly, if there were an ocean large enough, Saturn
would float on it.
This indicates that it is largely comprised of gases, like hydrogen and helium.
Under the thick outer layer of gas, there is a layer of helium droplets around a solid
metallic layer, and a relatively small core at the center just like Jupiter’s, made
of iron, rock, and water.
Ammonia gas forms clouds near the surface that obscures the activity below, which is
why Saturn appears to be much smoother than Jupiter.
But beyond all this lies Saturn’s most striking feature, its prominent ring system.
These are thought to be remnants of the cloud of gas and dust that initially formed the
planet, though there are competing hypotheses that require the rings to be much younger.
Some say the rings are comprised of debris from moons that entered within Saturn’s
Roche limit, which in this context refers to the radius within which a moon will be
torn apart by the gravity of its planet, although more generally, this term applies just as
well to any smaller body orbiting a larger one, like a planet around a star.
In any case, the rings extend out to more than twice the planet’s radius, but are
only a few hundred meters thick, which is incredibly thin by astronomical standards.
Although they appear continuous from afar, they are actually just swarms of small icy
particles, ranging in size from a grain of sand to a school bus, orbiting at different
velocities depending on their distance from the planet.
There are gaps in the ring system that have formed due to complex gravitational interactions
amongst the particles as well as some of the more closely neighboring moons.
Speaking of moons, Saturn has lots of them, just like Jupiter does, so Saturn looks like
yet another mini solar system within the solar system.
There are at least 62 of them orbiting roughly within the equatorial plane, and most of them
have names derived from Greek mythology.
By far the largest of these moons is called Titan, made of ice and rock.
It is the second largest moon in the solar system after Jupiter’s Ganymede, and also
slightly larger than the planet Mercury.
It is relatively far from Saturn, and is thus rather cold, able to maintain an atmosphere,
being one of only two known moons to have one, and this atmosphere is composed largely
of nitrogen.
Clouds rain down liquid hydrocarbons like methane and ethane, making Titan the only
body in the solar system other than Earth to clearly have bodies of liquid on its surface.
The Titans were the race of Greek gods directly descended from the first primordial gods,
and for this reason, Saturn’s largest moons have names taken from these Titans.
The next largest after Titan and on either side of it are Rhea and Iapetus.
From there, the moons get smaller going inward, with Dione, Tethys, Enceladus, and Mimas.
Enceladus, which is similar to Europa, exhibits geyser activity, making it the smallest known
geologically active object in the solar system.
The Cassini spacecraft took pictures earlier in this century of Enceladus spouting plumes
of water and organic materials high above its surface.
For this reason, it is believed to hold a vast subsurface ocean ripe with the conditions
necessary for life to exist.
Beyond these seven moons, there are fifty-five more, but they are extremely small, negligible
in mass compared to the larger ones.
And with that, we have a solid picture of Saturn and the Saturnian system, so let’s
move on to the next planet on the list.