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!
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