Today, I am super excited. Why? Because I get to show you the amazing planet
that is Saturn. As far as the planets go, this is probably
my favourite planet outside of Earth. And I think by the end of this video, you
may agree with me, because thanks to the Cassini probe, we have some astonishing imagery of
this beautiful planet. I’m Alex McColgan, and you’re watching
Astrum, and in this video I will not only give you insights into some of the spectacular
Cassini images, but I will also give you an overview of almost everything you could want
to know about the 6th planet from the Sun. Saturn is big. It’s is a gas giant with an average radius
about nine times that of Earth, making it the second biggest planet in our Solar System. I say average radius, because its equatorial
and polar radii differ by almost 10%: 60,000 km at the equator, compared to 54,000 km from
pole to pole. With an average density of 0.687 g/cm3, it
is only one-eighth the average density of Earth, however, because its volume is so large,
Saturn’s mass is over 95 Earths. This low density makes Saturn the lightest
planet per cubic centimetre by far, and it’s is the only planet of the Solar System that
is less dense than water—about 30% less. So, if you had a bath toy of Saturn that shares
the same density as the planet, it would float! This is because Saturn is 96% hydrogen, which
is the lightest of the elements. However, average density doesn’t tell the
full picture of what a planet is like. Saturn is classified as a gas giant because
what we see of the planet is simply gas, it doesn’t have a rocky surface under the cloud
layer. However, Saturn is most certainly not gaseous
all the way through, it’s got too much mass for that. You see, the further into Saturn you go, the
higher the pressure builds. Eventually, the pressure becomes so great
that the hydrogen stops behaving like a gas and starts acting like a liquid. So, in a way, under Saturn’s atmosphere
is a liquid hydrogen ocean. Even further below that, it may be that there
is a metallic hydrogen layer, where the pressure is so great that hydrogen starts acting like
a metal, and beneath that could be a metallic and rocky core. We do know that Saturn has a very hot interior,
reaching 11,700 °C at the core. This is twice as hot as the surface of the
Sun. If we look at Saturn through the infrared,
we see Saturn's glow, represented in brilliant shades of electric blue, sapphire and mint
green. On the night side, where there is no sunlight,
Saturn's own thermal radiation lights things up. This light is generated deep within Saturn,
and works its way upward, eventually escaping into space. In fact, this infrared image reveals that
Saturn radiates 2.5 times more energy into space than it receives from the Sun. You may not have noticed, but Saturn's atmosphere
has a banded pattern similar to Jupiter's. If you increase the contrast when you look
at images of Saturn, this becomes more apparent. Saturn's bands are much less chaotic than
Jupiter’s, however, and are much wider near the equator. And ever wondered why Saturn is yellow? It’s believed to be due to ammonia crystals
in its upper atmosphere. But while the atmosphere of Saturn may appear
calm, the planet is actually extremely active. The winds on Saturn are the second fastest
among the Solar System's planets, after Neptune. They can be a blistering 1,800 km/h. Visible storms are also known to appear on
Saturn, like this one that lasted just under a year in 2011. It had been the pattern that every 30 or so
Earth years, the planet produces what is called a “Great White spot” which is a unique
but short-lived phenomenon believed to occur once every Saturnian year. However, we have spotted a few of them over
the last 30 years. If it does follow a 30-year pattern though,
we can expect another one anytime now. Sadly, even if it does happen, we will only
be able to see it through the Hubble Space Telescope as the Cassini mission ended a few
years back. Saturn has plenty of smaller storms too, where
lightning is often produced. Cassini has even detected the sound of the
thunder. But while this might sound weak, the sound
you are hearing is actually the radio waves produced by the lightning converted to audio. In reality, lightning on Saturn is about 1,000
times more powerful than what we see on Earth. Still talking about storms, but moving on
to the planet’s poles, we find that each pole has giant, permanent storms. NASA reported in November 2006 that Cassini
had observed a "hurricane-like" storm locked to the south pole that had a clearly defined
eyewall. Eyewall clouds had not previously been seen
on any planet other than Earth. The ring is similar to the eyewall of a hurricane,
but much larger. The clear air in the centre is warm, like
the eye of hurricane, but on Saturn it is locked to the pole, whereas a hurricane on
Earth drifts around. The north pole is even more unusual. There is a persistent hexagon shaped storm
that rotates with the planet, not with the atmosphere. The straight sides of the polar hexagon are
each about 13,800 km long, making them larger than the diameter of the Earth. Why does this happen and to such a large scale? We don’t really know. However, the speed differential and viscosity
parameters between atmospheric bands here are likely to be within certain margins to
allow such an unusual polygon to form. Lab tests have since been done where polygons
could form in a circular tank of liquid, rotated at different speeds at its centre and near
the outer boundary, so this is the leading theory at the moment. Interestingly, towards the centre of this
hexagon, another eye wall can also be found. While not anywhere near as strong as Jupiter’s,
Saturn does have a magnetosphere, potentially generated in the metallic hydrogen layer of
the planet. It is large, extending far beyond the planet,
and it is strong enough to deflect Solar wind from the Sun. And much like other planets with magnetospheres,
Saturn has auroras. Their location and brightness strongly depend
on the solar wind pressure. The aurora become brighter and move closer
to the poles when the Solar wind pressure increases. The same process produces auroras on both
Earth and Saturn, where electrons from the solar wind stream along magnetic field lines
directed into the upper atmosphere. There, they collide with atoms and molecules,
exciting them to higher energies. The atoms and molecules release this added
energy by radiating light at different colours and wavelengths. On Earth, this light is mostly from oxygen
atoms and nitrogen molecules. On Saturn, it is from hydrogen. The rings for me are one of the highlights
of the planet. Saturn has a prominent ring system that consists
of ten continuous main rings. While they are mainly named after letters
of the alphabet, the naming conventions are a little confusing, so bear with me. The first 5 rings, from the closest to the
planet outward are, the D ring, which is very faint, C ring, B Ring – which is the brightest
and widest of all the rings, A ring – which is the last of the large bright rings, and
then F ring. The rings extend from 66,000 km to 140,000
km above Saturn's centre and are made up mostly of water ice, with small amounts of dust and
rocks. If we look in the ultraviolet at a section
of the brightest rings, it shows there is more ice toward the outer part of the rings,
than in the inner part. The red in the image indicates sparser ringlets
likely made of 'dirty,' and possibly smaller particles than in the icier turquoise ringlets. If we look at a picture representing radio
occultation, we can judge the size of the individual particles that make up the rings. Color is used to represent information about
ring particle sizes based on the measured effects of three radio signals. Shades of red show regions where particles
are larger than 5 centimeters in diameter. Green shows particles smaller than 5 centimeters,
and blues show particles less than 1 centimeter in size. Overall, it’s thought that particles in
the rings aren’t bigger than 10m and most are microscopic in size. The main rings are thought to be as little
as 10m thick, to 1 km thick. We can see that the rings are not perfectly
symmetrical. During the planet’s equinox, the rings can
get a bit wonky. Look at the top of this video, where the B
ring meet the A ring. Zooming in on this structure reveals ridges
and spokes a couple of kms tall, their presence given away by their shadows. Zooming out again, we can see the scale of
how many spokes there are during this period. Oscillations happen all the time in the rings
though, perhaps due to the presence of a shepherd moon, or even just naturally. The differences, which can be seen all in
only a day, can be up to 200km. So, I’ve talked about the D, C, B, and A
rings, and also mentioned the F ring. The F ring can also get quite wonky, and has
a perfect example of what is called a shepherd moon. It’s called Prometheus, and it leaves a
beautiful ripple in the F ring as it orbits. Once during its 14.7-hour orbit of Saturn,
Prometheus, which is only 102km across, reaches the point in its elliptical path, where it
is farthest away from Saturn and closest to the F ring. At this point, Prometheus' gravity is just
strong enough to draw a "streamer" of material out of the core region of the F ring. And that’s what causes these ripples. So, what comes after the F ring? Well, this is where it gets confusing. First, you have the Janus or Epimetheus Ring,
G Ring, Pallene Ring and then the E Ring. I find this picture amazing, as these rings
are much more visible being backlit by the Sun. This bright blue ring is the E ring, you can
just about see the faint Pallene Ring at the top of the picture. The G ring is the next distinct ring, and
again you can just about see the Janus or Epimetheus ring at the top below it. And can you see us? We’re all in this picture too. Here’s Earth and the Moon! The very last ring is the newly discovered
Phoebe Ring, a huge yet disperse ring that extends far beyond Saturn. It’s so large, that if it were visible from
Earth, its apparent diameter would be the size of two full moons across. It probably originated from Saturn’s 200km
moon Phoebe, which had been battered in its past. Phoebe orbits just outside of the ring, and
probably keeps this dust contained from going outward. On the other hand, it is also suspected that
dust in this ring is falling inward, eventually falling onto Iapetus, Saturn’s outermost
regular moon. It has a bizarre combination of colours because
dust from the Phoebe ring settles on it, but because Iapetus is tidally locked, only one
side of the moon ever faces Saturn, with the backside of it exposed to the Phoebe Ring,
meaning it’s two faces look very different. So now you know about the rings. I think you’ll agree that they are so interesting
in their own right. Theories abound as to why they are there,
but simply we don’t know. We know that some of the moons are responsible
for some of the material there, and we also know that some of the material there is responsible
for some of the moons. And talking of moons, Saturn has least 82
of them! They come in all shapes and sizes, and most
uniquely, Saturn’s largest moon Titan, which is even bigger than Mercury, is the only moon
in the Solar System with a thick atmosphere around it, which I have done a separate video
about here. I’m also going to throw in here that Saturn
has the Death Star orbiting it, biding its time. We call it Mimas. Generally though, most of Saturn’s moons
are very small, only a few kilometres across. Lastly, I’m going to talk about Saturn’s
orbit. Saturn orbits about 9 to 10 times further
away from the Sun than Earth does, and one year on Saturn takes 30 Earth years. Funnily enough, a day on Saturn is different
depending on where you are situated. At the equator or at the poles, a day lasts
about 10 hours and 14 minutes. Everywhere else on Saturn, a day lasts 10
hours and 38 minutes. The issue is, because Saturn isn’t solid,
it’s not bound to rotate at the same speed all over. I just want to leave you with this. Few sights in the solar system are more strikingly
beautiful than softly hued Saturn embraced by the shadows of its rings. The gas planet's subtle northward gradation
from gold to azure is a striking visual effect that scientists don't fully understand. Current thinking says that it may be related
to seasonal influences, tied to the cold temperatures in the winter hemisphere. And despite all that we have learned from
Cassini, Saturn remains a world of mystery. Thanks for watching! Did you enjoy this video? Then please like and share it, your support
really helps this channel to grow so I can make videos like these in the future. A big thank you as well to my Patrons and
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out the link in the description. And finally, if you want to learn more about
the various planets in our solar system, check out this playlist here. All the best and see you next time.
