Saturn: Crash Course Astronomy #18
Summary
TLDRThis episode of Crash Course explores Saturn, the solar system's second largest and least dense planet, known for its stunning rings and rapid rotation. Saturn's atmosphere, composed mainly of hydrogen and helium, hides a likely rocky core. The planet's oblate shape and storms are visible through telescopes. Its hexagonal vortex and massive rings, made of countless ice particles, are shaped by gravitational interactions with its moons. Saturn's moons, particularly Titan with its thick atmosphere and methane lakes, and Enceladus with its subsurface ocean and geysers, present intriguing possibilities for life beyond Earth.
Takeaways
- đ Saturn is the second largest and least dense planet in the solar system, with a density lower than water.
- đ It is a gas giant with a thick atmosphere composed mostly of hydrogen and helium, along with trace gases like methane and ammonia.
- đ Saturn has a rapid rotation, completing a day in just over ten and a half hours, resulting in an oblate shape.
- đȘ The planet features storms and a unique hexagonal vortex at its north pole, with winds reaching up to 500 kilometers per hour.
- đ Saturn's rings are expansive, spanning 250,000 kilometers across, and incredibly thin, averaging only about ten meters in thickness.
- đ The rings are believed to be composed of countless small chunks of nearly pure water ice, each orbiting the planet independently.
- đ Saturn has a complex system of rings with gaps and divisions, such as the Cassini Division, caused by the gravitational influence of its moons.
- đ Titan, one of Saturn's moons, is larger than Mercury and has a thick atmosphere and surface lakes of liquid methane.
- đ§ Enceladus, another Saturnian moon, has geysers of water erupting from its south pole, indicating a subsurface ocean.
- đ Saturn's system includes over 60 known moons, each with unique characteristics and potential for further scientific discovery.
- đ Observing Saturn through a telescope has been a significant source of inspiration for many astronomers and space enthusiasts.
Q & A
What is the most striking feature of Saturn's atmosphere?
-Saturn's atmosphere is most notably characterized by its thick atmosphere composed mostly of hydrogen and helium, with trace gases like methane and ammonia. It also has a banded pattern, similar to Jupiter's, but fainter due to its greater distance from the Sun and a deeper atmosphere.
Why is Saturn considered to be the least dense of the planets in the solar system?
-Saturn is considered the least dense planet because its density is about 2/3rds that of water, which is less than the density of water on Earth.
How long does it take for Saturn to complete a day?
-Saturn spins very quickly, completing a day in just 10.5 hours.
What is the nature of Saturn's storms?
-Saturn experiences oval hurricanes that pop up occasionally. In 2010, a massive storm erupted in its northern hemisphere, which grew so large it wrapped around the planet, reaching over 300,000 kilometers in length.
What is the unusual feature at Saturn's north pole?
-Saturn's north pole has a huge hexagonal vortex, a well-defined six-sided shape that is a natural outcome of a spinning fluid in the planet's atmosphere.
What are Saturn's rings made of and why are they not solid?
-Saturn's rings are made of countless small chunks of nearly pure water ice. They are not solid because if they were, the inner edge would orbit the planet much faster than the outer edge, causing them to be torn apart.
How large are Saturn's rings in comparison to the distance between Earth and the Moon?
-Saturn's rings are 250,000 kilometers across, which would cover â of the distance between Earth and the Moon if Saturn were placed between them.
Why are Saturn's rings so thin?
-Saturn's rings are incredibly thin, averaging about ten meters in thickness, due to the gravitational effects of Saturn and the original formation process of the rings, which could have involved a disrupted icy moon or a differentiated moon that lost its icy layer.
What is the Cassini Division and how was it discovered?
-The Cassini Division is a gap between Saturn's A and B rings, about 5,000 kilometers across. It was discovered by the Italian astronomer Giovanni Domenico Cassini and is maintained by the gravitational influence of the moon Mimas.
What are some unique features of Saturn's moons Titan and Enceladus?
-Titan is Saturn's largest moon, bigger than Mercury, with a thick atmosphere and lakes of methane. Enceladus is smaller but has an undersurface ocean and eruptions of water geysers, making both moons interesting candidates for potential life.
What is the significance of the statement 'Saturn is the crown jewel of the solar system'?
-The statement highlights the visual beauty and scientific intrigue of Saturn. Its stunning rings, diverse moons, and atmospheric phenomena make it a highlight of astronomical study and observation.
Outlines
đȘ Saturn: The Gas Giant with a Unique Hexagon
This paragraph introduces Saturn as the last of the naked-eye planets, highlighting its status as the second largest but least dense planet in the solar system. It delves into Saturn's composition, including its possible rocky core, layers of ice and metallic hydrogen, and a thick atmosphere primarily of hydrogen and helium. The summary mentions Saturn's rapid rotation, resulting in an oblate shape, and its visible cloud tops made of ammonia ices. The paragraph also covers Saturn's atmospheric banding, storms, and the distinctive hexagonal vortex at the north pole. The iconic rings of Saturn are discussed, explaining their composition of water ice chunks and their surprisingly thin profile, as well as theories about their formation.
đ Saturn's Rings and Moons: A Cosmic Dance
This section explores the intricacies of Saturn's ring system, including the discovery of the Cassini Division and the role of Saturn's moons in creating gaps and ringlets within the rings. It describes the dynamics of the F ring, maintained by the gravitational influence of moons Prometheus and Pandora. The paragraph also discusses the phenomena of wave formations in the rings caused by the interaction of small moons with the ring particles. Two of Saturn's moons, Mimas and Titan, are highlighted: Mimas for its massive crater and role in the Cassini Division, and Titan for its substantial atmosphere, hydrocarbon dunes, and potential for subsurface liquid water. The possibility of life on Titan, given its weather, atmosphere, and organic molecules, is also considered.
đž Saturn's Moons: A Menagerie of Celestial Oddities
The final paragraph delves into Saturn's diverse moons, focusing on Enceladus with its reflective surface, potential for cryovolcanism, and discovery of geysers, suggesting an undersurface ocean. It touches on the possibility of life on Enceladus, given the presence of organic molecules in its geysers. The paragraph also mentions other peculiar moons of Saturn, such as Iapetus with its walnut-like shape and Hyperion with its sponge-like, porous nature. It concludes with a personal note from the author about the inspirational impact of observing Saturn through a telescope and the scientific and aesthetic wonder it represents, ending with credits for the Crash Course Astronomy production team.
Mindmap
Keywords
đĄSaturn
đĄGas Giant
đĄOblate
đĄAtmosphere
đĄRings
đĄHexagonal Vortex
đĄMoons
đĄTitan
đĄEnceladus
đĄCryovolcanism
đĄResonance
Highlights
Saturn is the second largest planet in the solar system but has the least density, and would theoretically float in a large enough bathtub.
Saturn is a gas giant with a thick atmosphere, likely containing a rocky core surrounded by layers of ice and metallic hydrogen.
The atmosphere of Saturn is mostly hydrogen with trace gases like methane and ammonia, giving it a density about 2/3 that of water.
Saturn completes a rotation on its axis in just 10.5 hours, making it significantly oblate.
The cloud tops of Saturn are visible from Earth and are composed mostly of ammonia ices.
Saturn's atmosphere has faint banded patterns, likely due to its distance from the Sun and deeper atmosphere compared to Jupiter.
Saturn experiences oval hurricanes and a massive storm in 2010 that wrapped around the planet and persisted for years.
A unique hexagonal vortex is present at Saturn's north pole, a natural outcome of the planet's spinning fluid dynamics.
Saturn's rings, first seen by Galileo, were later identified by Christiaan Huygens as a ring system surrounding the planet.
The rings of Saturn are made of countless small chunks of nearly pure water ice, each orbiting the planet independently.
Saturn's rings are incredibly thin, averaging about ten meters in thickness, making them thinner than a sheet of paper when scaled.
Saturn's main rings are named A, B, and C, with the B ring being the broadest and the Cassini Division separating the A and B rings.
The gravity of Saturn's moons creates gaps and resonances in the rings, influencing their structure and stability.
Saturn's moon Titan is larger than Mercury and has a thick atmosphere composed mostly of nitrogen with traces of methane and hydrogen.
Titan has lakes of liquid methane on its surface, indicating weather patterns driven by methane rather than water.
Saturn's moon Enceladus has geysers of water erupting from its south pole, indicating a subsurface ocean.
The possibility of life on Saturn's moons Titan and Enceladus is considered due to their unique atmospheric and subsurface conditions.
Saturn has a diverse array of over 60 moons, each with unique characteristics and potential for scientific discovery.
Personal anecdotes from astronomers often credit their first telescope view of Saturn as the inspiration for their career choice.
Transcripts
This episode of Crash Course is brought to you by Squarespace.
So now weâve come to the last of the naked eye planets in the solar system: Saturn. Itâs
the second largest planet, but ironically the least dense. In fact, if you could find
a bathtub big enough, Saturn would float in it!
But it would leave a ring.
OK, thatâs the oldest joke in astronomy, but itâs true. Saturn is a gas giant, which
means it has a thick atmosphere. Like Jupiter, it probably has a rocky core several times
the mass of Earth, surrounded by layers of ice and weird, metallic hydrogen. On top of
all that is its atmosphere, hundreds of kilometers deep, composed mostly of hydrogen, with a
smaller amount of helium and a whole bunch of trace gases like methane and ammonia.
Overall, its density is about 2/3rds that of water. It wouldnât really float, though;
its gravity would draw in all the water from the giant bathtub⊠although, actually, come
to think of it, a bathtub filled with water big enough to put Saturn in would have more
mass than the planet, so the water would pull Saturn in.
Astronomy is fun!
Saturn spins really quickly, completing a day in just ten and a half hours. Its rapid
rotation and low density means itâs really oblate, or squished; itâs 10% wider through
the Equator than through the poles! Thatâs really noticeable through a telescope.
When we look at Saturn, we only see its cloud tops. Those clouds are mostly ammonia ices,
with water clouds lower down. The atmosphere is banded, like Jupiterâs, but the pattern
is much fainter, probably due to Saturn being farther from the Sun and therefore colder,
as well as the atmosphere being deeper than Jupiterâs too.
Thatâs not to say Saturn doesnât have storms. Oval hurricanes pop up every now and
again, and in 2010 a huge storm erupted in Saturnâs northern hemisphere. It was discovered
by an amateur astronomer, and Cassini spacecraft pictures showed it getting so big it literally
wrapped around the planet, reaching a length of over 300,000 kilometers! Traces of it persisted for years.
One of the most striking features on Saturn is a huge, hexagonal vortex at its north pole.
Vortices like this are common on planets; Earth and Venus have them too. That well-defined
six-sided shape is pretty freaky, but itâs actually a natural outcome of a spinning fluidâthe
air circulating Saturnâs atmosphereâwhich itself is in a spinning systemâin this case,
the planet itself. Itâs not that different than Earthâs jet stream, but itâs a lot
bigger, about 20,000 kilometers across⊠wider than Earth. And right at its center,
over Saturnâs north pole, is a ridiculously beautiful storm system about 2000 kilometers
across. Wind speeds there have been clocked at 500 kilometers per hour.
Saturn as a planet is of course an amazing place, but câmon. When you think Saturn,
you think rings. As well you should.
Saturnâs rings were seen by Galileo, but his telescope lacked the resolution to really
figure out what they wereâhe thought Saturn might be three objects in close proximity.
Some decades later the Dutch scientist Christiaan Huygens correctly interpreted their appearance
as a ring surrounding the planet.
Theyâre not solid. If they were theyâd get torn apart, since the inner edge would
orbit the planet way faster than the outer edge. Theyâre actually made of countless
small chunks of very nearly pure water ice. Each particle orbits the planet independentlyâŠ
so I guess Saturn wins in the âwhich planet has the most moonsâ category.
What really gets me about Saturnâs rings is their scale. Theyâre 250,000 kilometers
across. If you put Saturn between the Earth and Moon, the rings would cover â that distance.
And yet, despite their size, theyâre incredibly thin: They average about ten meters thick.
And no, I did not misspeak, I meant ten meters. Ten meters.
Thatâs amazing. Thatâs thinner, to scale, than a sheet of paper. Way thinner: If you
shrank Saturn down to the size of a piece of paper, that paper would be ten thousand
times thicker than the rings.
So yeah, Saturnâs rings are flat. But why?
Well thatâs tied to their origin, though the specifics of how they came to be arenât
exactly known. One idea is that they were originally an icy moon that got disrupted
by a huge collision. The shattered moon particles would have spread around Saturn, and any of
them that were on a tilted orbit would quickly collide with others, and in the end that would
average out all their orbits to form a flattened ring.
Or maybe there was once a large moon near Saturn, that was big enough to be differentiated;
that means the rocky bits fell to the moonâs core, while the ice stayed near the surface.
As it plowed through the material around the protoSaturn, the moonâs icy layer got stripped
off, forming the rings. And again, that would form a very flat disk.
However they formed, collisions would quickly flatten the ring out. And remember, Saturn
is oblate, so as the rings formed they wouldâve felt a gravitational tug from Saturnâs equatorial
bulge, centering them right over the planetâs midline.
Saturn has three main rings, give or take. In classic imaginative astronomer fashion,
theyâre given the names A, B, and Câin order of their discovery. B is the broadest,
roughly 26,000 kilometers wide. A is outside B, while the C ring is fainter and inside the B ring.
When the rings were first observed, the A and B rings were thought to be one ring. But
then the Italian astronomer Giovanni Domenico Cassini discovered a gap between them, and
we now call that the Cassini Division. Itâs about 5000 kilometers across, but itâs not
empty! There are quite a few very narrow rings inside of it.
The gap is due to one of Saturnâs moons, Mimas. If youâre an ice particle in the
Cassini division, you orbit Saturn twice for every one time Mimas goes around. This is
called a resonance, and it means that the particles at that location get tugged repeatedly
by the gravity of Mimas, which in essence yanks them out of their orbit.
There are quite a few gaps in the rings caused by moons; in fact, there are hundreds of âringletsâ
in the main rings. Even weirder, the F ring is outside the A ring, and is very narrow,
just a few hundred kilometers across. Itâs kept that way by two moons, Prometheus and
Pandora, orbiting just inside and outside the ring. They tug on the ring particles in
such a way that keeps them confined to very strict orbits; if a particle wanders out,
the moonsâ gravity drags it back in.
As the moons and ring particles interact, they can also create weird rippling waves
in the rings. And this is really cool: when small moons orbit Saturn on slightly inclined
orbits; it can create waves in the rings, tremendous vertical excursions that can reach
several kilometers high.
Saturn is weird.
And so are its moons. I already mentioned Mimas, an icy moon that carves out the Cassini
Division with its gravity. It also suffered a massive impact long ago that created a single
huge crater, making it look somehow familiar.
But Saturn has two moons specifically you should know about. The first is Titan, a monster
satellite thatâs actually bigger than Mercury, not that much smaller than Mars, and second
in moon size ranking only to Jupiterâs moon Ganymede. Titan not only has a substantial
atmosphereâthe only moon to have oneâbut itâs thicker than our air on Earth! I wouldnât
suggest breathing it, though: Itâs mostly nitrogen, with a smattering of methane and
hydrogen. Itâs also a hundred and eighty below zero Celsius there. Definitely donât
stick your tongue on a flagpole on Titan.
Titanâs atmosphere has a thick layer of haze that prevents us from seeing the surface
using visible light. But using infrared and radar, though, the Cassini spacecraft, which
has been orbiting Saturn since 2004, is able to map the surface. It also deployed a probe
named Huygens to land on Titanâs surface, the first time humanity had ever landed on
an outer solar system moon.
What they saw was an odd world, Earth-like in some ways, and very alien in many others.
Titan has wind-sculpted dunes, but theyâre made of hydrocarbon grains, not sand. There
are hints of volcanoes that spew liquid water instead of lava. These are called cryovolcanoes,
cold volcanoes, a term I love. This, together with measurements of Titanâs gravitational
field, have scientists thinking that Titan may have an underground ocean of liquid water.
Intriguingly, Titan also has long, winding channels indicating flows of some kind of
liquid on its surface. But it canât be water; itâs far too cold on the surface for that.
So what kind of liquid could it be? Well, Cassini also spotted quite a few flat regions
near Titanâs north and south poles. These have since been confirmed to be lakes of liquid
methaneâthe first time any liquid has been seen on the surface of another world. The
shorelines of the lakes appear to change over time, too, hinting very strongly that Titan
has weather, driven by methane as opposed to water here on Earth.
Weather, atmosphere, surface liquids, and an abundance of organic, carbon-based moleculesâŠ
could there be life on Titan? The conditions there areâŠinteresting. We obviously donât
know yet, but itâs an exciting possibility.
And itâs not the only Saturnian moon scientists are looking at for signs of life. Enceladus
is a smaller, icy moon about 500 km across: About the size of my home state of Colorado
or the southern part of England. Enceladus is incredibly shiny, reflecting nearly all
the light that hits it: a strong indicator itâs covered in water ice.
Parts of it are cratered, but other parts are very smooth, indicating some event resurfaced
the moon. The surface also has an extensive series of cracks in it, much like Jupiterâs
moon Europa. Scientists suspected cryovolcanism, and that was confirmed quite dramatically
in 2005 when Cassini spotted active geysers of water spewing from the south pole of Enceladus!
The water is erupting from a series of cracks nicknamed âtiger stripesâ, and is coming
from deep under the surface. Like Europa, Enceladus has an undersurface ocean, kept
liquid by Saturnâs ferocious tides, which squeeze the moon as it orbits the planet.
The plumes reach several hundred kilometers from the moonâs surface, and Cassini even
flew directly through the plumes, and detected organic molecules.
Could Enceladus be yet another harbor for life in the solar system? Again, no one knows,
but Iâd put it in the top three places to look, including Europa and Titan. Itâs weird,
isnât it? Weâve always looked for planets where conditions were like here on Earth,
but it turns out extremely cold moons may be the best places to seek out new life.
Saturn has a huge retinue of other moons, too, and theyâre all pretty weird. Iapetus
is shaped like a walnut, with a tall ridge of mountains encircling its equator; no oneâs
quite sure how that formed. Hyperion looks like a huge piece of Styrofoam thatâs been
hit repeatedly with a BB gunâand thatâs not a bad analogy, since it has such a low
density itâs likely to be extremely porous, like a sponge. A lot of Saturnâs moons orbit
the planet backwards, retrograde; similar to several moons of Jupiter. These may be
captured asteroids, or even Kuiper Belt Objects, giant chunks of ice that weâll learn about
very soon in a future episode. All in all, Saturn has over 60 moons weâve discovered so far.
I want to add a personal note. When you ask astronomers or astronauts what got them started,
what was the very first thing that happened to them to inspire them to do what they do,
overwhelmingly they will tell you: âI saw Saturn through a telescope.â
Itâs true. Itâs true for me; I remember my parents buying a cheap department store
telescope when I was five or six, setting it up in our driveway, and aiming it at Saturn.
I still remember seeing Saturn in the eyepiece, a perfect jewel, the rings small but vivid
and sharp. Itâs hard to believe itâs real when you see it, and even after all these
years, itâs my favorite target when Iâm stargazing. Iâll never get tired of watching
peoplesâ faces when they see it for the first time. They gasp, they their eyes get
wide, their mouths drops openâitâs honestly one of the greatest joys of life.
Saturn is the crown jewel of the solar system. Itâs the best kind of astronomical object:
Visually stunning, artistically gorgeous, and filled to overflowing with incredible science.
Today you learned that Saturn is a gas giant, and has a broad set of rings made of ice particles.
Moons create gaps in the rings via their gravity. Saturn has dozens of moons, including Titan,
which is as big as Mercury and has a thick atmosphere and lakes of methane; and Enceladus
which has an undersurface ocean and eruptions of water geysers. And, though we donât know
for sure, itâs possible either or both moons may support life.
Crash Course Astronomy is produced in association with PBS Digital Studios. Head on over to
their channel and discover more awesome videos. This episode was written by me, Phil Plait.
The script was edited by Blake de Pastino, and our consultant is Dr. Michelle Thaller.
It was directed by Nicholas Jenkins, edited by Nicole Sweeney, and the graphics team is Thought Café.
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