Solar System (2024) s01e05 Episode Script
Strange Worlds
1
We all know the familiar
faces of our solar system.
The worlds we grew up with.
But there's another
side to our solar system
we're now discovering.
The misfits and oddballs.
Worlds of freakish shape and size.
Of extreme landscapes
..mysterious phenomena
..and hidden secrets.
Our neighbourhood is far
stranger than we ever imagined.
So, how did all these
weird worlds come about?
Well, to answer that question,
we'll have to explore
the force that sculpted
and created them - gravity -
and the forces that resist
its relentless inward pull.
And also, at a deeper level,
because there's always a deeper level,
we'll be forced to contemplate why
there is anything of complexity
and beauty in our universe at all.
Welcome to the solar
system of the weird.
From a cloud of gas and dust,
gravity, the great
sculptor of our universe,
fashioned our star and all the worlds
and moons around it
..creating the solar system.
And gravity has continued to shape
these myriad worlds ever since.
Let me give you a little
30-second lecture on gravity.
And I'm going to use Newton's picture,
not Einstein's,
because we don't need
the additional accuracy
delivered by relativity.
Gravity is a force of
attraction between objects -
and it only attracts,
so that means that it tends
to clump things together.
And it's a force that only depends
on the distance between objects,
not the angle,
and so it tends to make spheres.
It's this property of gravity
..that shaped the moons and planets.
But beyond the near-perfect spheres
that dominate our solar system
..out past the giant orbs
..of gas and ice
..in a distant realm
of the solar system
..we found something strange.
Only one craft has been
sent to explore the worlds
of this distant region.
And on its epic, ongoing journey,
the probe caught a glimpse
of something truly bizarre
moving in the dark.
Not a sphere like
Earth, or even Pluto
..but a giant,
2,000-kilometre-long egg-shaped world.
Orbiting around it,
two glittering moons.
Mountains of icy rock and a faint ring.
If you were standing
on Haumea's surface,
the stars would wheel above you six
times faster than here on Earth.
Haumea is a truly unexpected
and bizarre-shaped object.
The first like it ever discovered.
Leaving the question
..what created such a seemingly
gravity-defying world?
Now, for rocky worlds,
the force resisting the
inward pull of gravity
is created by this,
the rigidity of the rock.
And the thing about pressure
is that it acts equally
outwards in all directions,
so if you have a force that's
squashing everything inwards,
equally in all directions,
and a force that's
resisting that squashing,
equally in all directions,
then the shape that's
naturally produced is a sphere.
And you might say, well,
why is something like that
not a sphere, then?
I mean, it's made of rock,
it's got a gravitational pull,
but it's a very weak gravitational pull
because it's not very massive.
And that's the point.
So the gravitational
forces on the surface here
trying to squash it down
are nowhere near big enough
to overcome the strength of the rock.
So, how big does a thing have to be
such that the gravitational
force is strong enough
to overcome the strength of the rock
and allow it to deform into a sphere?
And you find,
if you wave your hands around a bit,
that that size, the
radius, is something like
200, 300km.
It's called the potato radius.
And indeed, you find that,
if you look out into the solar system,
anything that's smaller than about
a couple of hundred kilometres
in radius looks like that.
And anything that's bigger than
a couple of hundred kilometres
in radius looks like the Earth.
From what we observe,
it seems that the potato radius is
a pretty strictly-followed rule.
The larger worlds are,
the more spherical they become.
Yet it's a rule Haumea breaks.
Way over the potato radius,
Haumea should be a round world.
So, if its egg shape is
not down to its size,
then what is it?
There is a clue,
found by looking at our world
in a slightly unusual way.
This is a photograph of us
working on the beach today.
I use the term loosely.
And what we did is we took a time-lapse.
But it's an interesting time-lapse.
We used an astronomical mount,
and so we fixed the camera at
a single point in the sky -
the Sun.
And then, can you see what happens?
So, it's holding its position.
It doesn't look right
because the whole ground
is rotating around.
So, usually, our experience
on the surface of the Earth
is watching the sky and the
sun and the moon and the stars
rotate around us.
But if you take that motion out,
then what you're seeing
here is the Earth
rotating beneath the sky.
This unusual view really
brings home the fact
that we live on a spinning ball of rock.
And there are consequences
for sitting on the surface
of something that's spinning.
New forces are introduced,
forces that are so called
fictitious forces -
but there's nothing
fictitious about them.
Actually, you'll know that
if you've tried to hang on
to a spinning roundabout.
If you let go, you go flying off.
That's not a fiction.
And that force is called
the centrifugal force.
Like the Earth,
all worlds in the solar system spin.
But Haumea is spinning
incredibly quickly.
The entire 2,000-kilometre-long world
..whips around once every four hours.
And that makes the centrifugal
force very powerful indeed.
And I can show you
..by taking a small thing
..let's say that's Haumea
..and spinning it really fast.
So, can you see what's happening?
It was a sphere,
and now it's bulging out.
And it's bulging out along its equator.
Look at that.
That's because the centrifugal force
tends to flatten things.
See?!
You see that?
I mean, there it is, right?
Those are fictitious forces at work.
And that's essentially,
actually, what happened
to some bits of Haumea, we think.
We think it was spinning so fast
that some bits got thrown off.
And
In fact, there it is.
So what you just saw
there was a demonstration
of how we think this system was created.
This is the best photo
we have of that system.
And these bits are essentially that bit
that's now over there somewhere.
There we are. If you look.
Haumea.
The battle between spin
and gravity has created
a truly strange world.
Gravity shapes everything
in the solar system,
and our next destination
has the scars to prove it.
Let the pull from our
star draw us inwards
..past Neptune
..until we reach the
inner most ice giant.
Uranus is pretty odd to begin with.
The entire planet is
knocked over on its side,
likely by a giant impact in the past.
But it's not only the
planet that's strange.
Voyager 2 is the only spacecraft
to have visited the moon Miranda.
As it flew past the south pole
..its cameras saw a truly
weird patchwork landscape.
A jumble of towering mountains
the height of Everest
and plunging chasms deeper
than the Grand Canyon.
One of the most astonishing
surfaces in all the solar system
..where strange cliffs rise
to unimaginable heights
..unlike anything seen on Earth.
So, what created the truly
bizarre face of Miranda?
The geology of our
world is awe-inspiring,
even though we're
really familiar with it.
I mean, this island rises
two and a half kilometres
from the surface of the Atlantic Ocean.
But just imagine what it would
be like standing on the surface
of Miranda.
I mean, there's a slope not unlike this
that stretches for something
like 10,000 metres.
And I remember when Voyager 2 arrived
at Miranda in 1986
and sent back images like this.
That slope is up here.
But one of the scientists at the time
said that this world is exotic.
And you can see why.
One of the explanations
for why it's like this
was that it must have
been hit by something
and then reassembled.
It's like a Frankenstein world.
But we now know the explanation
for this strange geology is,
if anything, even more exotic.
We're pretty sure that Miranda
must receive the occasional impact.
The result would look like it
was playing out in slow motion.
Debris taking the best
part of ten minutes
to slowly tumble to the
bottom of those great slopes.
On Earth, it would take only 50 seconds
to fall the same distance.
Because on this moon -
smaller than the width of the UK -
the pull of gravity is much weaker.
One hundredth of the
strength on our world.
Now, the basic explanation
for Miranda's strange surface
really is just basic physics.
Miranda's very small.
It's only about 470km in diameter -
not too far away from the potato radius.
And so its gravity is just
not quite strong enough
to squash it down into a sphere.
But there's more to the geology,
to the surface of a world,
than just basic physical principles.
There's also the history of the world.
Miranda's weak gravity is what
makes this landscape possible,
but it's not alone
responsible for sculpting it.
Something must have happened to Miranda
to create its battered
and scarred surface.
All we have to go on are
the glimpses of this world
captured as Voyager 2 flew by
..which suggest this
moon had a troubled past.
The key to unlocking
the mystery of Miranda
is to notice that this surface
is not as chaotic as it looks.
It's not entirely random.
There are these three distinct regions,
which are known as Corona.
And at least on these
two external regions,
there are ridges,
fault lines that surround them -
and to a geologist that's a smoking gun.
What it suggests is that this surface
was not created by external forces,
by impacts from the outside -
it was created from within.
And it's similar to this landscape here.
This is new land.
These are volcanoes.
They were created by a
hot spot deep underneath
the surface of the Earth -
and by buoyant hot material rising up
through the surface
of the Atlantic Ocean.
And we think that's
what's happened here.
Buoyant, less dense material
rising to the surface,
creating these features.
It's thought that it was
this internal turmoil
that left ruler-straight canyons
running for hundreds of kilometres
across the face of the moon.
Formed when warm material,
pushing up from the interior,
caused the surface to
crack along fault lines.
Part of the active geology
that, over millions of years,
created this Frankenstein world.
But that raises another mystery,
because Earth's geology
is driven by the heat
stored away from its formation
four and a half billion years ago,
along with the energy
released by radioactive decay.
But Miranda is far too
small to have retained
any of the heat from its formation.
So, where did all that energy come from?
For the answer, you have to
look at Miranda's relationship
with its parent planet,
and another quirk of gravity.
Probably several times in its history,
Miranda was in a more
elliptical orbit around Uranus.
That meant that it went
close to the planet,
far away, close and far away.
And the changing gravitational
forces injected the heat
into the moon,
and that's what drove its geology.
Gravity sculpting one of
the most tortured landscapes
in the Solar System.
I think the story of Miranda reveals
something quite deep, actually,
about the way that the
laws of nature sculpted
the strange worlds in our solar system,
and actually the way that they sculpt
everything in the universe.
Because the basic shape,
in this case a sphere,
reflects the simplicity
and beauty and symmetry
of the laws of nature that created it -
in this case gravity.
But the detail of the surface,
the complexity reflects a
turbulent and often chaotic past.
So you're seeing history frozen in time.
And it is this interaction
between simplicity
and symmetry and complexity
that truly makes our universe beautiful.
Beautiful and strange.
Travel further into the solar system
and we enter the realm
of the outer gas giant.
Home to a sight unrivalled
in the solar system.
A structure of outrageous
size and shape.
Rings of rock and ice.
Split into hundreds of ordered,
repeating tracks and gaps
almost engineered in their precision
..and looping for
thousands of kilometres
through the void.
So, how did nature create the
intricate, ordered beauty,
the spiralling gaps and
tracks of Saturn's rings?
One of the most obvious things
you can say about our universe
is that, at first sight,
it is very complicated indeed.
But one of the deepest
things you can say about it
is that complexity emerges from
the action of very simple laws.
If you just think about
this desert landscape -
there's all these beautiful
sand dunes and ripples.
But if you look more closely,
there's regularity in the ripples.
And if you look at the sand dunes,
this angle that they fall
away at is always the same.
So there's regularity
and beauty and structure
emerging from the action of simple laws.
In this case,
it's just the wind blowing sand grains
and gravity pulling
them down to the ground.
And I think the best and certainly
the most evocative example
of that in the solar system
has to be the rings of Saturn.
Yet at first sight, there's nothing
simple about Saturn's rings.
We think they formed when an icy moon
strayed too close to Saturn
..and was pulled apart by its gravity
..creating a jumble of trillions
of individual fragments of ice.
So, what turned such chaos into the
ordered beauty of Saturn's rings?
Nasa's Cassini probe captured
the rings in stunning detail.
And orbiting within them,
it saw one of the most startling objects
in the entire Saturnian system.
Pan is the most
wonderful, bizarre object.
I mean, look at these
photographs taken by Cassini.
I mean, this is
It looks like a cross between a UFO
and a piece of pasta.
And it's really small!
It's less than 30km in diameter.
But its impact on the rings is profound.
The shape, actually, is the key
to understanding how it is that
Saturn's rings are so
wonderfully complex.
And you can see the basic idea
..here.
So, there's Pan.
And the moon is orbiting
inside the ring.
And so that means that ring particles
can essentially hit them.
They fall onto the surface.
And because Pan has got a
very weak gravitational field,
it's too small - way
below the potato radius.
They don't get squashed into a sphere.
They stay there, sort of a ridge.
So part of the explanation for the gaps
is that the rings are
slowly being eaten.
For millions of years,
Pan has been nibbling away,
clearing icy particles out of its orbit.
And yet,
Pan is only 28km across -
but it sits within a track
that is over 300km wide.
Clearly far broader than Pan could
clear through snacking alone.
This moon doesn't just create
a tiny gap in the rings.
It creates a very big gap indeed.
It's so big, in fact,
it's called the Encke Gap.
That gap was discovered using
19th century telescopes.
It's about ten times the
diameter of the moon.
And the way it does that is
really key to understanding
the complexity of Saturn's rings.
So, I have to tell you one thing,
a very important thing about orbits.
Here's Saturn.
And here is Pan, orbiting around.
Now, it's a property of orbits
that the further away
from the planet you are,
the slower you move.
That's actually traced back all the way
to the beautiful
simplicity of Newton's law
of universal gravitation.
So that means that ring particles
on the inside of Pan
are orbiting faster.
They're overtaking the moon.
These particles get a gravitational tug
that tends to slow them down.
They are pulled back by Pan's gravity.
And ring particles further
out are moving slower.
Right, now Pan is overtaking them.
And that tends to give
them a gravitational kick
which speeds them up.
And the effect of that
is that Pan's gravitational
pull on the particles
that are overtaking it tends
to cause them to fall
down towards the planet
and its gravitational pull
on the particles outside -
that it's overtaking -
tend to get raised to a higher
orbit around the planet.
And so Pan clears a much
bigger gap in the rings
than you might otherwise expect.
And Pan is not alone.
Daphnis,
a moon a mere 8km across,
clears its own track.
Tiny worlds
creating structures
on a staggering scale.
What's more puzzling is that so far
these are the only moons
we've seen directly
clearing a track like this.
But there are thousands of
looping spirals and gaps
seemingly created by nothing at all.
Including one of the biggest -
the Cassini Division -
over 3,000 kilometres wide.
So, what's creating
these other structures?
Surprisingly,
the answer lies not within the rings
but out beyond the discs of ice.
There really is tremendous complexity
and structure in Saturn's rings.
Not only gaps,
but also sort of structures -
density waves that
wrap around the planet,
often several times,
like the grooves on a record.
And all those structures ultimately
are caused by hundreds of moons.
Actually, over 140 largish
moons at the last count -
and countless smaller ones.
And all those have a gravitational
influence on the particles
in the rings.
One of the key culprits or drivers
of complexity is this moon,
which looks like a space station
- but it's not a space station.
It's a moon. It's called Mimas.
Another truly odd,
almost science fiction world
..with its dominant impact crater.
Yet it's not obvious why this
moon should influence the rings,
as it's about 40,000km away.
So, Mimas,
it's orbiting outside the rings,
such that it goes round Saturn once
for every two orbits
of particles that would be
inside the Cassini Division.
So that means that those
particles would regularly meet
Mimas on its orbit.
There's a gravitational interaction,
that disrupts the orbits
of these particles
and moves them out of the division.
Each time the moon and
the ice particles align,
Mimas' gravity tugs at the
fragments of ice and rock
like an invisible hand.
Over millions of years
opening up the giant gap.
And Mimas is just one of
over 140 known moons
..each capable of creating their
own resonances with the rings.
Look at this picture. This is an image
from the Cassini spacecraft.
And you see the complexity
here - it's mind boggling.
This is a resonance with
a moon called Prometheus
that orbits 14 times around Saturn
for every 15 orbits of
the particles in there.
And that causes this disruption,
this structure in the rings.
Here's a moon called Janus.
That creates a recognisable structure
in the rings, and so on.
And these are just the
structures that we've observed.
The orbital dance of Saturn's moons
recorded in the rings.
Creating a pattern we're lucky to see.
Imagine how complicated
the gravitational field
is around Saturn,
and that's what you're seeing.
It's very beautiful.
It's as if someone had
sprinkled ice crystals
over the gravitational
field so that we can see it.
And I suppose that a vinyl record
really is a bit like Saturn's rings.
There's a structure here, a physical
structure, which can give rise
to something that we can perceive
now - sound made solid, in a sense.
When you put a needle on there
A stylus needle All right, Grandad!
But also there is of course a
sense of history about a recording
on a record.
It tells you something about the past.
And so it is with the pattern
that we see in the rings.
In Saturn's rings we can see gravity
at work, shaping our Solar System.
Over half a billion
kilometres closer to the Sun
is a planet on a mind-boggling scale,
so huge you could fit all
the other planets inside it.
Jupiter's immense gravity has
helped shape an astonishing world.
Since 2016, Nasa's Juno spacecraft
has been exploring
Jupiter and its moons
..including the largest
moon in the Solar System.
Ganymede is a very strange world indeed.
A moon playing at being a planet.
It's the only moon we know of
with an internally generated
magnetic field,
producing strange aurora.
And elsewhere on its surface,
Juno witnessed bizarre scars
gouged into its icy crust.
These phenomena suggest Ganymede may
be hiding an extraordinary secret.
Ganymede is becoming,
I think it's fair to say,
one of the most fascinating
places in the Solar System.
This is one of our best images
of Ganymede, taken by Juno.
It is a big moon.
This is the eighth largest
object orbiting the Sun,
bigger than Mercury and
not much smaller than Mars.
But it doesn't look particularly
different from our Moon.
But a series of observations
are beginning to suggest to us
that there may be something
extremely interesting indeed
going on below the surface.
One clue comes from Ganymede's aurora.
Detailed observations have shown that it
behaves in an unexpected way.
To have an aurora, then a planet
or moon needs two things basically,
it needs a tenuous atmosphere
and it needs a magnetic field.
So, what's happening on Ganymede
is that charged particles,
primarily from Jupiter, they're
being funnelled down the magnetic
field lines to the poles,
and there they hit particles in the
atmosphere, they excite them and
cause them to emit light, to glow.
And that's the same process that we see
here on Earth in the
Northern and Southern Lights.
However,
Jupiter also has a magnetic field,
and that will affect
the aurora on Ganymede.
And so what was done is some
computer modelling. You get Ganymede
with its field and its aurora,
and you get Jupiter with its magnetic
field and you put it all into the
computer and you see what happens,
and you find there is a prediction,
that the aurora on Ganymede
should kind of wobble around,
wander in the vicinity of the pole.
And we observed that.
But we observed that the aurora
wanders far less than it should,
so that implies there's
something else going on.
If Ganymede had an additional,
second magnetic field,
it would interfere with the
aurora, causing it to wander less.
But the only way to generate
that extra field would be
if another layer within the
moon conducts electricity.
I really was never very good in the lab.
No, it doesn't work!
- Have we got another battery? - Yeah.
- Let's plug another battery in.
Here's an electrical circuit.
There's a battery and a bulb.
And if I connect it, the electrons
flow and the bulb lights up.
But now, look what happens
if I take these two wires,
but connect it by dipping
the wires into salt water.
Very cool, isn't it? So,
in here the circuit is being completed.
Saltwater is a conductor of electricity.
An electrical current flows and
that can produce a magnetic field.
So, we think that is the origin
of that third magnetic field
that's making the aurora
wander far less than it should.
The implication is,
that beneath the surface of Ganymede,
there's a saltwater ocean.
Welcome to the largest ocean
of water in the Solar System.
It's estimated that there's
a layer of water over 100km
deep wrapped around the moon.
One that never sees the light of day,
hidden beneath 150km of rock-hard ice.
But how can liquid water
exist in such enormous
quantities beneath the frozen surface?
One fascinating theory involves
those strange gouges in the surface.
These are impact craters.
Not single craters,
like those found on other worlds
..but long chains.
You know, quite a lot of the answer
actually of how it came to be
that Ganymede has an ocean
is the presence of Jupiter.
Yeah, I can see clouds on the
surface of Jupiter through
this pretty small telescope,
even though tonight
it's about 600 million kilometres away.
You can fit over 1,000 Earths inside it.
It's massive.
And being massive, it means it's
got a strong gravitational pull.
And Jupiter tends to attract things,
suck things in that come within
its vicinity and rip them apart.
And we've seen that.
This is a great image.
It's one of the most famous images
in astronomy in recent times, actually.
And you see that?
So, that is comet Shoemaker-Levy 9.
This is a comet that came
too close to Jupiter,
it was drawn in by its
gravitational field, ripped to
bits by its gravitational field,
and then ultimately hit Jupiter.
And it hit Jupiter with
such ferocity that we saw
the impact in the clouds.
And some of them were
bigger than the Earth.
Now, you look at that
..and then look at that -
the surface of Ganymede.
Being so close to Jupiter puts
Ganymede in the firing line.
Ferocious impacts
..that create the chain craters.
These scars are just a fraction
of what Ganymede has suffered,
living so close to Jupiter.
And that's key to understanding how
it may have got its hidden ocean.
The early Solar System was a much
more chaotic place than it is today.
Impacts were common.
Everything got hit.
Jupiter's immense gravity drew in
countless asteroids and comets
..and Ganymede was
caught in the crossfire.
Impacts delivered enough
energy to heat the moon
..and kick start a process
that caused it to melt
and separate into layers.
Dense heavy metals at the core
..and an outer shell
made of water and ice.
And we think Ganymede has
retained enough of that heat
to produce a saltwater ocean with
more water actually than all the
oceans of the Earth combined below
the frozen surface of Ganymede.
A strange giant moon with an ocean
and aurora nearly a billion
kilometres away from the Sun.
We're talking about
potentially a habitat for life.
This is a big world, a planet-sized
moon, which has a magnetic field
and a saltwater ocean and a
ready source of energy, it seems.
All the things that we think are
necessary for the origin of life.
And it's important because we
used to think of what's called
a habitable zone around a
star, which is where the
Earth orbits, and indeed Mars and
Venus, just about,
which is the zone where you
could potentially have liquid
water on the world, on the
surface of the world in that case.
But now looking at places like this,
we understand that there
might be habitable zones far
away from stars, in this case a
habitable zone around a gas giant.
And that habitability here
is delivered by gravity.
Leaving this distant ocean moon behind,
we head inwards on the
final leg of our journey
..passing through the asteroid belt,
rubble left over from when gravity
failed to pull a planet together
..until we reach the
inner rocky planets.
The worlds here are home to phenomena
and landscapes that are mesmerising.
So strange and alien.
But amongst all these wonders
lurks perhaps the
strangest world of all.
Welcome to Earth.
It is the biggest rocky world.
Radius about 6,370 kilometres or so.
It's a bit unusual in that
it's got a single moon,
but the thing that makes
it very unusual indeed
is the presence of that -
liquid water on the surface.
You might not think of Earth as strange,
because we live on it,
but it is in fact a very rare world.
You know, this is a really wonderful
and unusual thing to be able
to do in our Solar System,
because there is no other
world where the conditions
of temperature and pressure on the
surface allow liquid water to exist.
It's a very narrow range.
And that range is set by the
details of our atmosphere.
There are tons
Tons of atmosphere pressing down
on this rock pool to stop
it from boiling away.
The nature of our atmosphere
is defined by the history
of our world, our place in
the Solar System and gravity.
Now, if you imagine that you'd
reduced the mass of the planet
just a bit, then the pressure would
fall and this would boil away.
If I carried on doing that
and reduced the gravitational
pull some more, the whole atmosphere
would disappear off into space.
All the myriad properties
of our planet have combined,
to allow liquid water to persist
here for over four billion years
..leading to planet Earth's
most unique feature
..life.
As we explore the Solar System,
we're discovering ever
stranger places
.all born of the interplay
between beautifully simple
laws of nature
..and the deep history of
each and every world
..creating endless wonders
of the Solar System
..including
..us.
Just look at these telescopes,
our eyes on the universe.
Now, I find it so remarkable that
on one strange world in our Solar
System, collections of atoms have
come together that can do astronomy,
because there's nothing particularly
special about the Earth.
It is just another lump of stuff
that has found a way to
avoid gravitational collapse.
But somewhere in between
the relentless inward
pull of gravity and the sheer
bloody mindedness of matter,
some of that stuff has
found a way to contemplate
its place in the universe.
No other planet has rings quite
like Saturn does. They're beautiful.
But it's odd to think that they
might not be there forever.
Far from a permanent structure,
we now know that these
strange loops of rock
and ice are constantly changing and
may one day disappear completely.
We have big questions
about Saturn's rings.
How old are the rings?
How did they form and what
is their evolution like?
How long are they going to last?
Nasa's Cassini spacecraft studied Saturn
and its rings for 13 years
in search of answers.
Cassini allowed us to see
Saturn from closer up than ever
before, but also from new
vantage points that we had never
been able to access from the Earth.
Cassini witnessed a
series of bizarre moons,
clearing paths in the rings.
But one of the biggest insights
came from its encounter with
a strange kind of rain
falling onto Saturn.
It was Voyager that gave us
the first hints that particles
could be falling into Saturn.
Towards the end of the Cassini mission,
when we flew the spacecraft between
the rings and the planet, we were
able to detect small ring particles
that were falling into the planet,
so-called ring rain.
The immense gravity of Saturn
is pulling on these particles,
eroding the rings.
Ring rain causes the
rings to slowly die.
But what we don't know is the rate
at which the rings are perishing.
We just know that they are.
Flying through the icy rain
falling from ring to planet was
one of Cassini's last endeavours.
In 2017, the mission came to an
end before Cassini could find out
how long the rings had left.
To get a definitive answer on
the lifespan of Saturn's rings,
we needed a brand-new mission.
So, JWST isn't like a normal telescope
that you would find on Earth.
It's not at the top of
a mountain like the big
telescopes that we have here.
Instead, it is 1.5 million
kilometres away in space.
The space telescope is designed
to peer into the depths of the universe.
But its infrared cameras
are also showing us
our Solar System in a
strange new light
..illuminating the faint
rings around the outer planets
normally invisible to us.
It's extremely difficult to
get to the outer Solar System,
and so an instrument like JWS
that can look at these distant
objects is invaluable.
Amongst its targets is
Saturn and its rings
..where the hope is that the
telescope will be able to help
answer how fast the
ring rain is falling.
So the rings are made
of mostly water ice
and some of the smallest pieces
flow up the magnetic field
and fall into the planet.
That happens all the way around,
so in our observations,
we see this kind of infrared glow
all the way around the
planet, that location,
which indicates that there
is ring material flowing in.
In the next few years,
JWST will measure the intensity
of the infrared glow in that band,
revealing how fast the rings
are losing particles
I'm very excited to find out
how quickly Saturn's
rings are eroding today
because finding out
what's going on today
is really important
for mapping their past
and predicting their future.
..bringing us ever closer
to understanding exactly how
long Saturn's stunning rings
of ice are likely to last.
There's something about
seeing Saturn's rings.
You have this almost
childlike fascination
and a professional curiosity that
come together in a very unique way.
Knowing that Saturn's rings won't
be around forever and that we're
here at the exact moment when
they are here is really amazing.
I feel really lucky that
we get to experience them.
We all know the familiar
faces of our solar system.
The worlds we grew up with.
But there's another
side to our solar system
we're now discovering.
The misfits and oddballs.
Worlds of freakish shape and size.
Of extreme landscapes
..mysterious phenomena
..and hidden secrets.
Our neighbourhood is far
stranger than we ever imagined.
So, how did all these
weird worlds come about?
Well, to answer that question,
we'll have to explore
the force that sculpted
and created them - gravity -
and the forces that resist
its relentless inward pull.
And also, at a deeper level,
because there's always a deeper level,
we'll be forced to contemplate why
there is anything of complexity
and beauty in our universe at all.
Welcome to the solar
system of the weird.
From a cloud of gas and dust,
gravity, the great
sculptor of our universe,
fashioned our star and all the worlds
and moons around it
..creating the solar system.
And gravity has continued to shape
these myriad worlds ever since.
Let me give you a little
30-second lecture on gravity.
And I'm going to use Newton's picture,
not Einstein's,
because we don't need
the additional accuracy
delivered by relativity.
Gravity is a force of
attraction between objects -
and it only attracts,
so that means that it tends
to clump things together.
And it's a force that only depends
on the distance between objects,
not the angle,
and so it tends to make spheres.
It's this property of gravity
..that shaped the moons and planets.
But beyond the near-perfect spheres
that dominate our solar system
..out past the giant orbs
..of gas and ice
..in a distant realm
of the solar system
..we found something strange.
Only one craft has been
sent to explore the worlds
of this distant region.
And on its epic, ongoing journey,
the probe caught a glimpse
of something truly bizarre
moving in the dark.
Not a sphere like
Earth, or even Pluto
..but a giant,
2,000-kilometre-long egg-shaped world.
Orbiting around it,
two glittering moons.
Mountains of icy rock and a faint ring.
If you were standing
on Haumea's surface,
the stars would wheel above you six
times faster than here on Earth.
Haumea is a truly unexpected
and bizarre-shaped object.
The first like it ever discovered.
Leaving the question
..what created such a seemingly
gravity-defying world?
Now, for rocky worlds,
the force resisting the
inward pull of gravity
is created by this,
the rigidity of the rock.
And the thing about pressure
is that it acts equally
outwards in all directions,
so if you have a force that's
squashing everything inwards,
equally in all directions,
and a force that's
resisting that squashing,
equally in all directions,
then the shape that's
naturally produced is a sphere.
And you might say, well,
why is something like that
not a sphere, then?
I mean, it's made of rock,
it's got a gravitational pull,
but it's a very weak gravitational pull
because it's not very massive.
And that's the point.
So the gravitational
forces on the surface here
trying to squash it down
are nowhere near big enough
to overcome the strength of the rock.
So, how big does a thing have to be
such that the gravitational
force is strong enough
to overcome the strength of the rock
and allow it to deform into a sphere?
And you find,
if you wave your hands around a bit,
that that size, the
radius, is something like
200, 300km.
It's called the potato radius.
And indeed, you find that,
if you look out into the solar system,
anything that's smaller than about
a couple of hundred kilometres
in radius looks like that.
And anything that's bigger than
a couple of hundred kilometres
in radius looks like the Earth.
From what we observe,
it seems that the potato radius is
a pretty strictly-followed rule.
The larger worlds are,
the more spherical they become.
Yet it's a rule Haumea breaks.
Way over the potato radius,
Haumea should be a round world.
So, if its egg shape is
not down to its size,
then what is it?
There is a clue,
found by looking at our world
in a slightly unusual way.
This is a photograph of us
working on the beach today.
I use the term loosely.
And what we did is we took a time-lapse.
But it's an interesting time-lapse.
We used an astronomical mount,
and so we fixed the camera at
a single point in the sky -
the Sun.
And then, can you see what happens?
So, it's holding its position.
It doesn't look right
because the whole ground
is rotating around.
So, usually, our experience
on the surface of the Earth
is watching the sky and the
sun and the moon and the stars
rotate around us.
But if you take that motion out,
then what you're seeing
here is the Earth
rotating beneath the sky.
This unusual view really
brings home the fact
that we live on a spinning ball of rock.
And there are consequences
for sitting on the surface
of something that's spinning.
New forces are introduced,
forces that are so called
fictitious forces -
but there's nothing
fictitious about them.
Actually, you'll know that
if you've tried to hang on
to a spinning roundabout.
If you let go, you go flying off.
That's not a fiction.
And that force is called
the centrifugal force.
Like the Earth,
all worlds in the solar system spin.
But Haumea is spinning
incredibly quickly.
The entire 2,000-kilometre-long world
..whips around once every four hours.
And that makes the centrifugal
force very powerful indeed.
And I can show you
..by taking a small thing
..let's say that's Haumea
..and spinning it really fast.
So, can you see what's happening?
It was a sphere,
and now it's bulging out.
And it's bulging out along its equator.
Look at that.
That's because the centrifugal force
tends to flatten things.
See?!
You see that?
I mean, there it is, right?
Those are fictitious forces at work.
And that's essentially,
actually, what happened
to some bits of Haumea, we think.
We think it was spinning so fast
that some bits got thrown off.
And
In fact, there it is.
So what you just saw
there was a demonstration
of how we think this system was created.
This is the best photo
we have of that system.
And these bits are essentially that bit
that's now over there somewhere.
There we are. If you look.
Haumea.
The battle between spin
and gravity has created
a truly strange world.
Gravity shapes everything
in the solar system,
and our next destination
has the scars to prove it.
Let the pull from our
star draw us inwards
..past Neptune
..until we reach the
inner most ice giant.
Uranus is pretty odd to begin with.
The entire planet is
knocked over on its side,
likely by a giant impact in the past.
But it's not only the
planet that's strange.
Voyager 2 is the only spacecraft
to have visited the moon Miranda.
As it flew past the south pole
..its cameras saw a truly
weird patchwork landscape.
A jumble of towering mountains
the height of Everest
and plunging chasms deeper
than the Grand Canyon.
One of the most astonishing
surfaces in all the solar system
..where strange cliffs rise
to unimaginable heights
..unlike anything seen on Earth.
So, what created the truly
bizarre face of Miranda?
The geology of our
world is awe-inspiring,
even though we're
really familiar with it.
I mean, this island rises
two and a half kilometres
from the surface of the Atlantic Ocean.
But just imagine what it would
be like standing on the surface
of Miranda.
I mean, there's a slope not unlike this
that stretches for something
like 10,000 metres.
And I remember when Voyager 2 arrived
at Miranda in 1986
and sent back images like this.
That slope is up here.
But one of the scientists at the time
said that this world is exotic.
And you can see why.
One of the explanations
for why it's like this
was that it must have
been hit by something
and then reassembled.
It's like a Frankenstein world.
But we now know the explanation
for this strange geology is,
if anything, even more exotic.
We're pretty sure that Miranda
must receive the occasional impact.
The result would look like it
was playing out in slow motion.
Debris taking the best
part of ten minutes
to slowly tumble to the
bottom of those great slopes.
On Earth, it would take only 50 seconds
to fall the same distance.
Because on this moon -
smaller than the width of the UK -
the pull of gravity is much weaker.
One hundredth of the
strength on our world.
Now, the basic explanation
for Miranda's strange surface
really is just basic physics.
Miranda's very small.
It's only about 470km in diameter -
not too far away from the potato radius.
And so its gravity is just
not quite strong enough
to squash it down into a sphere.
But there's more to the geology,
to the surface of a world,
than just basic physical principles.
There's also the history of the world.
Miranda's weak gravity is what
makes this landscape possible,
but it's not alone
responsible for sculpting it.
Something must have happened to Miranda
to create its battered
and scarred surface.
All we have to go on are
the glimpses of this world
captured as Voyager 2 flew by
..which suggest this
moon had a troubled past.
The key to unlocking
the mystery of Miranda
is to notice that this surface
is not as chaotic as it looks.
It's not entirely random.
There are these three distinct regions,
which are known as Corona.
And at least on these
two external regions,
there are ridges,
fault lines that surround them -
and to a geologist that's a smoking gun.
What it suggests is that this surface
was not created by external forces,
by impacts from the outside -
it was created from within.
And it's similar to this landscape here.
This is new land.
These are volcanoes.
They were created by a
hot spot deep underneath
the surface of the Earth -
and by buoyant hot material rising up
through the surface
of the Atlantic Ocean.
And we think that's
what's happened here.
Buoyant, less dense material
rising to the surface,
creating these features.
It's thought that it was
this internal turmoil
that left ruler-straight canyons
running for hundreds of kilometres
across the face of the moon.
Formed when warm material,
pushing up from the interior,
caused the surface to
crack along fault lines.
Part of the active geology
that, over millions of years,
created this Frankenstein world.
But that raises another mystery,
because Earth's geology
is driven by the heat
stored away from its formation
four and a half billion years ago,
along with the energy
released by radioactive decay.
But Miranda is far too
small to have retained
any of the heat from its formation.
So, where did all that energy come from?
For the answer, you have to
look at Miranda's relationship
with its parent planet,
and another quirk of gravity.
Probably several times in its history,
Miranda was in a more
elliptical orbit around Uranus.
That meant that it went
close to the planet,
far away, close and far away.
And the changing gravitational
forces injected the heat
into the moon,
and that's what drove its geology.
Gravity sculpting one of
the most tortured landscapes
in the Solar System.
I think the story of Miranda reveals
something quite deep, actually,
about the way that the
laws of nature sculpted
the strange worlds in our solar system,
and actually the way that they sculpt
everything in the universe.
Because the basic shape,
in this case a sphere,
reflects the simplicity
and beauty and symmetry
of the laws of nature that created it -
in this case gravity.
But the detail of the surface,
the complexity reflects a
turbulent and often chaotic past.
So you're seeing history frozen in time.
And it is this interaction
between simplicity
and symmetry and complexity
that truly makes our universe beautiful.
Beautiful and strange.
Travel further into the solar system
and we enter the realm
of the outer gas giant.
Home to a sight unrivalled
in the solar system.
A structure of outrageous
size and shape.
Rings of rock and ice.
Split into hundreds of ordered,
repeating tracks and gaps
almost engineered in their precision
..and looping for
thousands of kilometres
through the void.
So, how did nature create the
intricate, ordered beauty,
the spiralling gaps and
tracks of Saturn's rings?
One of the most obvious things
you can say about our universe
is that, at first sight,
it is very complicated indeed.
But one of the deepest
things you can say about it
is that complexity emerges from
the action of very simple laws.
If you just think about
this desert landscape -
there's all these beautiful
sand dunes and ripples.
But if you look more closely,
there's regularity in the ripples.
And if you look at the sand dunes,
this angle that they fall
away at is always the same.
So there's regularity
and beauty and structure
emerging from the action of simple laws.
In this case,
it's just the wind blowing sand grains
and gravity pulling
them down to the ground.
And I think the best and certainly
the most evocative example
of that in the solar system
has to be the rings of Saturn.
Yet at first sight, there's nothing
simple about Saturn's rings.
We think they formed when an icy moon
strayed too close to Saturn
..and was pulled apart by its gravity
..creating a jumble of trillions
of individual fragments of ice.
So, what turned such chaos into the
ordered beauty of Saturn's rings?
Nasa's Cassini probe captured
the rings in stunning detail.
And orbiting within them,
it saw one of the most startling objects
in the entire Saturnian system.
Pan is the most
wonderful, bizarre object.
I mean, look at these
photographs taken by Cassini.
I mean, this is
It looks like a cross between a UFO
and a piece of pasta.
And it's really small!
It's less than 30km in diameter.
But its impact on the rings is profound.
The shape, actually, is the key
to understanding how it is that
Saturn's rings are so
wonderfully complex.
And you can see the basic idea
..here.
So, there's Pan.
And the moon is orbiting
inside the ring.
And so that means that ring particles
can essentially hit them.
They fall onto the surface.
And because Pan has got a
very weak gravitational field,
it's too small - way
below the potato radius.
They don't get squashed into a sphere.
They stay there, sort of a ridge.
So part of the explanation for the gaps
is that the rings are
slowly being eaten.
For millions of years,
Pan has been nibbling away,
clearing icy particles out of its orbit.
And yet,
Pan is only 28km across -
but it sits within a track
that is over 300km wide.
Clearly far broader than Pan could
clear through snacking alone.
This moon doesn't just create
a tiny gap in the rings.
It creates a very big gap indeed.
It's so big, in fact,
it's called the Encke Gap.
That gap was discovered using
19th century telescopes.
It's about ten times the
diameter of the moon.
And the way it does that is
really key to understanding
the complexity of Saturn's rings.
So, I have to tell you one thing,
a very important thing about orbits.
Here's Saturn.
And here is Pan, orbiting around.
Now, it's a property of orbits
that the further away
from the planet you are,
the slower you move.
That's actually traced back all the way
to the beautiful
simplicity of Newton's law
of universal gravitation.
So that means that ring particles
on the inside of Pan
are orbiting faster.
They're overtaking the moon.
These particles get a gravitational tug
that tends to slow them down.
They are pulled back by Pan's gravity.
And ring particles further
out are moving slower.
Right, now Pan is overtaking them.
And that tends to give
them a gravitational kick
which speeds them up.
And the effect of that
is that Pan's gravitational
pull on the particles
that are overtaking it tends
to cause them to fall
down towards the planet
and its gravitational pull
on the particles outside -
that it's overtaking -
tend to get raised to a higher
orbit around the planet.
And so Pan clears a much
bigger gap in the rings
than you might otherwise expect.
And Pan is not alone.
Daphnis,
a moon a mere 8km across,
clears its own track.
Tiny worlds
creating structures
on a staggering scale.
What's more puzzling is that so far
these are the only moons
we've seen directly
clearing a track like this.
But there are thousands of
looping spirals and gaps
seemingly created by nothing at all.
Including one of the biggest -
the Cassini Division -
over 3,000 kilometres wide.
So, what's creating
these other structures?
Surprisingly,
the answer lies not within the rings
but out beyond the discs of ice.
There really is tremendous complexity
and structure in Saturn's rings.
Not only gaps,
but also sort of structures -
density waves that
wrap around the planet,
often several times,
like the grooves on a record.
And all those structures ultimately
are caused by hundreds of moons.
Actually, over 140 largish
moons at the last count -
and countless smaller ones.
And all those have a gravitational
influence on the particles
in the rings.
One of the key culprits or drivers
of complexity is this moon,
which looks like a space station
- but it's not a space station.
It's a moon. It's called Mimas.
Another truly odd,
almost science fiction world
..with its dominant impact crater.
Yet it's not obvious why this
moon should influence the rings,
as it's about 40,000km away.
So, Mimas,
it's orbiting outside the rings,
such that it goes round Saturn once
for every two orbits
of particles that would be
inside the Cassini Division.
So that means that those
particles would regularly meet
Mimas on its orbit.
There's a gravitational interaction,
that disrupts the orbits
of these particles
and moves them out of the division.
Each time the moon and
the ice particles align,
Mimas' gravity tugs at the
fragments of ice and rock
like an invisible hand.
Over millions of years
opening up the giant gap.
And Mimas is just one of
over 140 known moons
..each capable of creating their
own resonances with the rings.
Look at this picture. This is an image
from the Cassini spacecraft.
And you see the complexity
here - it's mind boggling.
This is a resonance with
a moon called Prometheus
that orbits 14 times around Saturn
for every 15 orbits of
the particles in there.
And that causes this disruption,
this structure in the rings.
Here's a moon called Janus.
That creates a recognisable structure
in the rings, and so on.
And these are just the
structures that we've observed.
The orbital dance of Saturn's moons
recorded in the rings.
Creating a pattern we're lucky to see.
Imagine how complicated
the gravitational field
is around Saturn,
and that's what you're seeing.
It's very beautiful.
It's as if someone had
sprinkled ice crystals
over the gravitational
field so that we can see it.
And I suppose that a vinyl record
really is a bit like Saturn's rings.
There's a structure here, a physical
structure, which can give rise
to something that we can perceive
now - sound made solid, in a sense.
When you put a needle on there
A stylus needle All right, Grandad!
But also there is of course a
sense of history about a recording
on a record.
It tells you something about the past.
And so it is with the pattern
that we see in the rings.
In Saturn's rings we can see gravity
at work, shaping our Solar System.
Over half a billion
kilometres closer to the Sun
is a planet on a mind-boggling scale,
so huge you could fit all
the other planets inside it.
Jupiter's immense gravity has
helped shape an astonishing world.
Since 2016, Nasa's Juno spacecraft
has been exploring
Jupiter and its moons
..including the largest
moon in the Solar System.
Ganymede is a very strange world indeed.
A moon playing at being a planet.
It's the only moon we know of
with an internally generated
magnetic field,
producing strange aurora.
And elsewhere on its surface,
Juno witnessed bizarre scars
gouged into its icy crust.
These phenomena suggest Ganymede may
be hiding an extraordinary secret.
Ganymede is becoming,
I think it's fair to say,
one of the most fascinating
places in the Solar System.
This is one of our best images
of Ganymede, taken by Juno.
It is a big moon.
This is the eighth largest
object orbiting the Sun,
bigger than Mercury and
not much smaller than Mars.
But it doesn't look particularly
different from our Moon.
But a series of observations
are beginning to suggest to us
that there may be something
extremely interesting indeed
going on below the surface.
One clue comes from Ganymede's aurora.
Detailed observations have shown that it
behaves in an unexpected way.
To have an aurora, then a planet
or moon needs two things basically,
it needs a tenuous atmosphere
and it needs a magnetic field.
So, what's happening on Ganymede
is that charged particles,
primarily from Jupiter, they're
being funnelled down the magnetic
field lines to the poles,
and there they hit particles in the
atmosphere, they excite them and
cause them to emit light, to glow.
And that's the same process that we see
here on Earth in the
Northern and Southern Lights.
However,
Jupiter also has a magnetic field,
and that will affect
the aurora on Ganymede.
And so what was done is some
computer modelling. You get Ganymede
with its field and its aurora,
and you get Jupiter with its magnetic
field and you put it all into the
computer and you see what happens,
and you find there is a prediction,
that the aurora on Ganymede
should kind of wobble around,
wander in the vicinity of the pole.
And we observed that.
But we observed that the aurora
wanders far less than it should,
so that implies there's
something else going on.
If Ganymede had an additional,
second magnetic field,
it would interfere with the
aurora, causing it to wander less.
But the only way to generate
that extra field would be
if another layer within the
moon conducts electricity.
I really was never very good in the lab.
No, it doesn't work!
- Have we got another battery? - Yeah.
- Let's plug another battery in.
Here's an electrical circuit.
There's a battery and a bulb.
And if I connect it, the electrons
flow and the bulb lights up.
But now, look what happens
if I take these two wires,
but connect it by dipping
the wires into salt water.
Very cool, isn't it? So,
in here the circuit is being completed.
Saltwater is a conductor of electricity.
An electrical current flows and
that can produce a magnetic field.
So, we think that is the origin
of that third magnetic field
that's making the aurora
wander far less than it should.
The implication is,
that beneath the surface of Ganymede,
there's a saltwater ocean.
Welcome to the largest ocean
of water in the Solar System.
It's estimated that there's
a layer of water over 100km
deep wrapped around the moon.
One that never sees the light of day,
hidden beneath 150km of rock-hard ice.
But how can liquid water
exist in such enormous
quantities beneath the frozen surface?
One fascinating theory involves
those strange gouges in the surface.
These are impact craters.
Not single craters,
like those found on other worlds
..but long chains.
You know, quite a lot of the answer
actually of how it came to be
that Ganymede has an ocean
is the presence of Jupiter.
Yeah, I can see clouds on the
surface of Jupiter through
this pretty small telescope,
even though tonight
it's about 600 million kilometres away.
You can fit over 1,000 Earths inside it.
It's massive.
And being massive, it means it's
got a strong gravitational pull.
And Jupiter tends to attract things,
suck things in that come within
its vicinity and rip them apart.
And we've seen that.
This is a great image.
It's one of the most famous images
in astronomy in recent times, actually.
And you see that?
So, that is comet Shoemaker-Levy 9.
This is a comet that came
too close to Jupiter,
it was drawn in by its
gravitational field, ripped to
bits by its gravitational field,
and then ultimately hit Jupiter.
And it hit Jupiter with
such ferocity that we saw
the impact in the clouds.
And some of them were
bigger than the Earth.
Now, you look at that
..and then look at that -
the surface of Ganymede.
Being so close to Jupiter puts
Ganymede in the firing line.
Ferocious impacts
..that create the chain craters.
These scars are just a fraction
of what Ganymede has suffered,
living so close to Jupiter.
And that's key to understanding how
it may have got its hidden ocean.
The early Solar System was a much
more chaotic place than it is today.
Impacts were common.
Everything got hit.
Jupiter's immense gravity drew in
countless asteroids and comets
..and Ganymede was
caught in the crossfire.
Impacts delivered enough
energy to heat the moon
..and kick start a process
that caused it to melt
and separate into layers.
Dense heavy metals at the core
..and an outer shell
made of water and ice.
And we think Ganymede has
retained enough of that heat
to produce a saltwater ocean with
more water actually than all the
oceans of the Earth combined below
the frozen surface of Ganymede.
A strange giant moon with an ocean
and aurora nearly a billion
kilometres away from the Sun.
We're talking about
potentially a habitat for life.
This is a big world, a planet-sized
moon, which has a magnetic field
and a saltwater ocean and a
ready source of energy, it seems.
All the things that we think are
necessary for the origin of life.
And it's important because we
used to think of what's called
a habitable zone around a
star, which is where the
Earth orbits, and indeed Mars and
Venus, just about,
which is the zone where you
could potentially have liquid
water on the world, on the
surface of the world in that case.
But now looking at places like this,
we understand that there
might be habitable zones far
away from stars, in this case a
habitable zone around a gas giant.
And that habitability here
is delivered by gravity.
Leaving this distant ocean moon behind,
we head inwards on the
final leg of our journey
..passing through the asteroid belt,
rubble left over from when gravity
failed to pull a planet together
..until we reach the
inner rocky planets.
The worlds here are home to phenomena
and landscapes that are mesmerising.
So strange and alien.
But amongst all these wonders
lurks perhaps the
strangest world of all.
Welcome to Earth.
It is the biggest rocky world.
Radius about 6,370 kilometres or so.
It's a bit unusual in that
it's got a single moon,
but the thing that makes
it very unusual indeed
is the presence of that -
liquid water on the surface.
You might not think of Earth as strange,
because we live on it,
but it is in fact a very rare world.
You know, this is a really wonderful
and unusual thing to be able
to do in our Solar System,
because there is no other
world where the conditions
of temperature and pressure on the
surface allow liquid water to exist.
It's a very narrow range.
And that range is set by the
details of our atmosphere.
There are tons
Tons of atmosphere pressing down
on this rock pool to stop
it from boiling away.
The nature of our atmosphere
is defined by the history
of our world, our place in
the Solar System and gravity.
Now, if you imagine that you'd
reduced the mass of the planet
just a bit, then the pressure would
fall and this would boil away.
If I carried on doing that
and reduced the gravitational
pull some more, the whole atmosphere
would disappear off into space.
All the myriad properties
of our planet have combined,
to allow liquid water to persist
here for over four billion years
..leading to planet Earth's
most unique feature
..life.
As we explore the Solar System,
we're discovering ever
stranger places
.all born of the interplay
between beautifully simple
laws of nature
..and the deep history of
each and every world
..creating endless wonders
of the Solar System
..including
..us.
Just look at these telescopes,
our eyes on the universe.
Now, I find it so remarkable that
on one strange world in our Solar
System, collections of atoms have
come together that can do astronomy,
because there's nothing particularly
special about the Earth.
It is just another lump of stuff
that has found a way to
avoid gravitational collapse.
But somewhere in between
the relentless inward
pull of gravity and the sheer
bloody mindedness of matter,
some of that stuff has
found a way to contemplate
its place in the universe.
No other planet has rings quite
like Saturn does. They're beautiful.
But it's odd to think that they
might not be there forever.
Far from a permanent structure,
we now know that these
strange loops of rock
and ice are constantly changing and
may one day disappear completely.
We have big questions
about Saturn's rings.
How old are the rings?
How did they form and what
is their evolution like?
How long are they going to last?
Nasa's Cassini spacecraft studied Saturn
and its rings for 13 years
in search of answers.
Cassini allowed us to see
Saturn from closer up than ever
before, but also from new
vantage points that we had never
been able to access from the Earth.
Cassini witnessed a
series of bizarre moons,
clearing paths in the rings.
But one of the biggest insights
came from its encounter with
a strange kind of rain
falling onto Saturn.
It was Voyager that gave us
the first hints that particles
could be falling into Saturn.
Towards the end of the Cassini mission,
when we flew the spacecraft between
the rings and the planet, we were
able to detect small ring particles
that were falling into the planet,
so-called ring rain.
The immense gravity of Saturn
is pulling on these particles,
eroding the rings.
Ring rain causes the
rings to slowly die.
But what we don't know is the rate
at which the rings are perishing.
We just know that they are.
Flying through the icy rain
falling from ring to planet was
one of Cassini's last endeavours.
In 2017, the mission came to an
end before Cassini could find out
how long the rings had left.
To get a definitive answer on
the lifespan of Saturn's rings,
we needed a brand-new mission.
So, JWST isn't like a normal telescope
that you would find on Earth.
It's not at the top of
a mountain like the big
telescopes that we have here.
Instead, it is 1.5 million
kilometres away in space.
The space telescope is designed
to peer into the depths of the universe.
But its infrared cameras
are also showing us
our Solar System in a
strange new light
..illuminating the faint
rings around the outer planets
normally invisible to us.
It's extremely difficult to
get to the outer Solar System,
and so an instrument like JWS
that can look at these distant
objects is invaluable.
Amongst its targets is
Saturn and its rings
..where the hope is that the
telescope will be able to help
answer how fast the
ring rain is falling.
So the rings are made
of mostly water ice
and some of the smallest pieces
flow up the magnetic field
and fall into the planet.
That happens all the way around,
so in our observations,
we see this kind of infrared glow
all the way around the
planet, that location,
which indicates that there
is ring material flowing in.
In the next few years,
JWST will measure the intensity
of the infrared glow in that band,
revealing how fast the rings
are losing particles
I'm very excited to find out
how quickly Saturn's
rings are eroding today
because finding out
what's going on today
is really important
for mapping their past
and predicting their future.
..bringing us ever closer
to understanding exactly how
long Saturn's stunning rings
of ice are likely to last.
There's something about
seeing Saturn's rings.
You have this almost
childlike fascination
and a professional curiosity that
come together in a very unique way.
Knowing that Saturn's rings won't
be around forever and that we're
here at the exact moment when
they are here is really amazing.
I feel really lucky that
we get to experience them.