Juice The Sky at Night

Good evening. In this programme, we're going to talk once again

about the giant planets Jupiter and Saturn.

We've learned so much in the last few years. Chris Lintott.

We certainly have and we've got a particularly exciting new mission.

ESA, the European Space Agency,

has decided its next big thing in space is going to be a mission

called Juice, that's going to go to Jupiter and explore its moons.

We've got two of the people who made Juice happen,

Michelle Dougherty from Imperial College London, and Leigh Fletcher from Oxford.

-Congratulations on being selected.

-Thank you very much.

-Michelle, what's Juice going to do?

OK, as you say, it was recently chosen and so the plan now is we will go into a study phase.

We will be launched in 2022. It will take eight years to get there.

And so reach the Jupiter system in 2030.

We'll spend at least three and a half years within the system and orbiting the moons.

You may still be doing The Sky At Night. I sadly won't.

Well, that remains to be seen. Which moons do you go to first?

We will fly past Europa first. We'll have flybys over Europa.

We will then have a Callisto phase which will be interesting,

not only because we're going to be looking at Callisto,

but we're going to be coming out of the equatorial plane.

That will allow us to get into regions we haven't seen before.

And then we will move to Ganymede and we'll spend nine months orbiting

around Ganymede and we will end the mission by crashing on the surface.

This is the first time a probe will have orbited a moon of one of the giant planets.

-Why are the moons so important?

-The Galilean moons, in particular,

each one has a very different unique environment that in its own right

would be worth studying, but the point of Juice,

the idea behind the mission, is to compare the conditions

that we find on those moons - Europa, Ganymede and Callisto.

Most of the moons of the outer solar system are made of ice.

That's simply because at the very cold temperatures

of the outer solar system, water exists in its frozen form.

So it makes up the large proportion of these moons.

The tantalising thing about these three moons

is that there is a source of energy that causes the ice to melt to become liquid water.

We believe that a liquid ocean exists beneath the surface

of these three icy moons.

That has huge implications for the potential for these moons

to be habitable.

That's not that they do support life right now, but it's that there is

the chance or the potential for life to exist on these icy worlds.

Michelle, what's this source of energy that keeps

-some of the ice liquid?

-In the environment around Jupiter,

most of the energy comes from the fast rotation of Jupiter.

But as far as the energy sources of the interior of the moons

is concerned, we think they're still hot in the interior

because of the tidal forces between Jupiter and the moon.

-As they go round Jupiter, they're pushed and pulled by its very powerful gravity.

-Yes.

And so that's what allows the interior of the moons

to still be warm, but there are two other things you need

if you're going to look for life.

You need there to be complex organic compounds

and you also need the environment to be stable over quite a long period of time.

You need water, you need heat, you need stability and you need chemicals.

-Is it ordinary water. H2O, like ours?

-We think it is, yes.

We also think that its conductivity,

the amount of salt we have in the water, is probably similar to ours.

But we're postulating from the observations we got from the Galilean spacecraft.

We need to get a spacecraft that will orbit around Ganymede,

make observations on the surface,

but also understand what's underneath.

These four ingredients Michelle was talking about,

Juice will be able to study and look

and so we'll finally be able to answer some of these questions

that Galileo, back in the 1990s through to 2003, they left open.

Planetary scientists since have been trying to resolve some of these questions.

Let's go back to Europa. You talked about recent activity on the surface,

but how recent are we talking about? Is this something that's happening now?

No. People have gone back to the Galileo observations and they've compared them

to observations that we have of the Greenland Ice Shelf.

You could almost convince yourself you were looking at the same thing.

The Greenland Ice Shelf changes over, what, thousands of years,

so we should expect that sort of timescale on Europa.

One of the interesting things about these regions of potentially

recent activity, recent on a geologic timescale, so long periods of time,

is there may be regions of the crust which are thinner than elsewhere,

where you've got an exchange of say energy

from the interior of this moon, up towards the icy surface.

So these fractured chaotic terrains are actually really

tantalising targets for future spacecraft like Juice,

especially if it has the capabilities to probe deep through

and beneath that icy crust. If we go for the thinner regions,

-we might get access to that icy ocean beneath.

-We come to Ganymede.

-The largest satellite in the entire solar system.

-That's right.

-Juice is going to go into orbit.

-That's right.

We thought long and hard about whether we wanted

to orbit around Europa or orbit around Ganymede and in fact,

Ganymede is more interesting, I think. As we know, it's the largest moon in the solar system.

It also is the only moon in the solar system that has an internal planetary field.

-It's got a dynamo field inside.

-Just like the Earth has.

It also has a magnetic field that's induced by currents

that are flowing in the ocean underneath, and so there's a mix

of these different fields that we need to try and understand.

-You care because they're telling you about the interior.

-Yes.

What do the surfaces of these outer moons look like?

You move the largest moon, Ganymede, out to Callisto.

Callisto has a very ancient and battered terrain.

We think it's a remnant of the very earliest bombardments that

took place within the solar system.

So this, if you like, is a much more inactive moon.

Some would say a dead moon, that isn't having resurfacing processes taking place.

Whereas on Ganymede, there's a higher probability that we might

see the evidence that activity has occurred in geologically recent history.

In fact, if you have... Ground based observers are able to resolve contrasts across Ganymede

and there's an ancient dark terrain called Galileo Regio,

which is visible in some of the best amateur images that we see.

Especially when Juice finally gets to Jupiter,

we'll have a huge amateur community there along with us,

observing the same features as the spacecraft is seeing up close and personal.

That's going to be one to watch.

Is this then a common way for moons in the solar system to be?

In all three, they're icy, they have underground oceans.

That must be telling us something about what's likely in the solar system.

Yes. That's one of the reasons we want Juice to go to the...

It's an unanswered question.

What we want to try and do with the three moons

we're going to focus on is get an understanding about why

they're different, try and understand what the heat source is,

we think we know what the heat source is,

but why is it having a different effect on all three of the moons?

But also, really try and understand

whether there are environments in our solar system

where the conditions are there, so that life might be able to form.

If we can understand that at Ganymede,

go into orbit around Ganymede and spend a lot of time

looking at it, it will allow us to then describe how we think

some of the bodies outside of our solar system might have formed

and some of the extra solar work that is being done as well.

If you can find planets in the Goldilocks Zone, around their star,

not too hot, not too cold, they may have icy moons as well.

And this is a revisiting of that Goldilocks hypothesis.

The idea that you have temperatures that are just right here

on Planet Earth for life to have existed.

These icy moons of the solar system, which traditionally, you don't think of as being part of...

-Cos they're far too cold.

-Far too cold, way too distant,

but actually they might have these four ingredients.

The stability with time, the energy source that's required

and the supply of materials in a liquid water environment.

Be nice to have some toothed fish wandering around as well.

I'm not sure if we can actually promise that's going to happen.

Not yet. Well, we've talked a great deal about Jupiter.

-On now to Saturn and its family of moons.

-Yes.

Cassini is orbiting around Saturn. Two of the moons are interesting,

partly because we can compare them to the moons of Jupiter.

And that is Enceladus and Titan.

We know both of those moons have got bodies of liquid underneath

the surface and so by learning more about Titan and Enceladus now,

we can feed that information

to what we're going to learn with Juice at Jupiter.

Shall we start with Enceladus? That's the icy moon.

So that seems closer to the Jovian examples,

but Enceladus is a weird place.

The Fountains of Enceladus are the weirdest things in the solar system.

-I think they are too, but it's weird in a fascinating way.

-We like weird!

But it's very clear that there is an energy source

at Enceladus that is keeping the interior heated.

We know that the water ice has become liquid and we know that

because water vapour is escaping.

We see amazing pictures of these. You detect them with other instruments as well.

We've flown through the plume, we've been able to measure

the amount of organics and dust and water vapour in the plume.

The really interesting thing from my perspective

is the amount of activity is changing over time.

It's very clear there are internal processes taking place,

which are changing from one week to the next.

So is this a special time now that we're able to view Enceladus with this happening?

Or is this something that could have been happening over hundreds of thousands of years in the past?

I think it must have been happening for a long period of time.

It's now very clear that Enceladus and its plumes is the source

of the earring and we know that the earring has been in existence...

-One of the outer of Saturn's rings?

-Yes.

It's one of the rings that you can't visually see.

We don't see anything like this on any of Jupiter's small moons.

-Why just Enceladus?

-Possible discoveries that we might make

when we have Europa flybys with Juice is maybe we will see something

at Europa, but it's very clear that Enceladus is unique, in the sense

it's small, it has this internal heat source that we didn't expect

to be there, and it's spewing out a large amount of water vapour.

We know that water vapour is salty, in some sense,

-or it's not just pure water.

-That's right.

-We know that because you've flown through it very bravely.

I don't know if they would want to do it again! The closest flyby we had was 25km above the surface.

And it was very clear after it happened that the mission planners will not do it again.

Because the mag boom sticks off from the side of the spacecraft

and the spacecraft moved a little bit more

than they thought it would, as we flew through the plume.

They don't want the spacecraft to tumble.

-It was a really rocky ride on the way through.

-I wonder why not(!)

But nonetheless, from this brave, plucky adventure

through the Fountains of Enceladus, it's like something out of sci-fi! Through the Fountains of Enceladus!

We discovered the water is salty, it has other material in there.

People have suggested that means there's a rocky core.

There might be a rocky core. We don't know.

A lot of work has been done at the moment,

trying to model what the interior actually looks like.

To understand it best, we'd need to go into orbit and that

is difficult to do because the gravitational field of Enceladus

is small, you need a huge amount of fuel to be able to get into orbit.

So we're going to have to make do with lots more flybys that we have

of Enceladus by the Cassini craft.

-Let's turn now to Titan, unlike any of the others.

-It has an atmosphere.

-And an interesting surface.

-Yes.

We haven't really got to see the surface until very recently.

The atmosphere is made up of ethane and methane.

It's almost like a very smoggy place, so you can't see through it.

It's only been with some of the instruments on board Cassini

we've been able to see through the atmosphere and onto the surface.

One of the initial disappointments with the Titan observations

was that we expected to see lots of liquid on the surface.

We didn't, for years.

And it's only very recently that the first signatures

of some type of liquid on the surface was seen.

We think that's probably

because no rain had fallen for a long period of time

and it was only after rain had fallen we got to see it.

We do see evolving weather through the Cassini mission.

We've seen clouds come and go on Titan.

We know there's something special about the north pole of Titan.

Large bodies of standing liquid, some combination of methane

and ethane and various hydrocarbons up there.

-Certainly not water.

-No.

One of the closest comparisons is like the liquid natural gas

sort of thing.

It's a fascinating region and the first time in planetary exploration

where we can really talk about one day exploring an ocean

on a surface and sailing a boat on the surface of another moon.

What strikes me from some of the shots, from Huygens,

the probe that landed on the surface,

you could see what looked like river valleys.

A very easy landscape to read. It looked very Earth-like.

Very cold, of course.

We're talking about Titan

because we were talking about worlds with oceans beneath the surface.

Is that the same sort of model that we have for Titan?

Or is the liquid confined to the surface?

No, there have been some radar observations of Titan

which seem to imply there is a body of liquid underneath the surface.

We're hoping with the magnetic field instrument to be able

to measure induced currents that are flowing in that ocean.

But we can't get close enough.

Because Titan has a dense atmosphere,

because we've got the boom sticking off the side, the mission planners

don't want to get us closer than about 950km

because as the atmosphere gets denser,

the spacecraft could begin to tumble.

So we hope we will get some observations of induced currents,

but we aren't sure we'll be able to do it.

And we want to keep the spacecraft alive until it goes into its polar orbits.

We've talked about some of Saturn's moons.

Let's now talk about the ringed planet itself.

There have been exciting times in Saturn recently.

Back in 2010, Cassini saw this gigantic spike

in the amount of lightning emission coming from the planet,

showing there was a gigantic thunderstorm evolving.

This thunderstorm grew to be what we describe as planetary in scale,

like a single Earth storm enveloping the entire latitude circle.

Cassini was very lucky to be there to see it.

That thunderstorm lasted from the end of 2010

through to the middle of 2011 when we thought things were starting

to die down, the lightning strikes were dying away,

and the churning convective activity of the storm had seemed to subside.

But it's not over.

Cassini is still tracking the remnants of this particular storm.

It had an effect on the atmosphere really high up

that can only been seen at infrared wavelengths of light

-and the storm is still raging.

-At infrared, you're detecting heat.

This is energy that's being injected into the upper layers

of the atmosphere. That's why you see it glowing.

On Earth, you fly in a plane, you try to get above these storm cells

to avoid all the turbulence and bumping that are inherent.

On Saturn, we didn't we really expect the same sort of things to be taking place.

You have this huge region of hot, heated gas,

many hundreds of kilometres higher up than those storm clouds.

The storm that's happening down at depth is having a huge effect

on the atmosphere hundreds of kilometres higher up.

We've never seen that anywhere in the solar system before.

It's exciting to be tracking this.

And we're seeing it as heat energy emitted by the planet Saturn

with Cassini's instruments.

Why do you think the atmospheres of Jupiter and Saturn are so different?

When you look at Jupiter, you're seeing right down to the region where the clouds condense.

You're seeing the fluffy white ammonia clouds

and possibly the ammonium hydrogen sulphide clouds.

On Saturn, above those clouds, there are haze particles.

The haze is so thick it reflects the light before the light gets down.

-It's almost like smog.

-Exactly. A bit like with Titan.

You can't see the surface because of all the smoggy hazy stuff.

Saturn, you can't see the cloud because of the smoggy hazy stuff.

Why are they different? Why does Saturn have this smog and Jupiter not?

There's a difference in size between these two planets.

It means that the gravitational acceleration on the two planets

-is very different.

-The pull of gravity.

All the cloud decks on Saturn are more spread out with altitude.

On Jupiter, they're more localised and squashed together.

The amount of a particular material,

say it's methane or ammonia or hydrogen sulphide available

to form a cloud is very different.

The thing that makes Jupiter have that red colour, we think,

has got something to do with phosphorus.

On Saturn, that phosphorus is locked away, deep in the interior.

It isn't able to get up to cause the red colouration of the clouds.

It's the difference in size that causes such great big differences

in the hazes and the chemistry at work within these atmospheres.

We've been talking about Juice. You've got a lot of work to do before you get to launch.

You've got lots of time off between launch and getting to Jupiter, I'm sure.

What do you think? If I had to force you all to choose one really big question,

either Jupiter or Saturn or their moons, to answer, what would it be?

I know what you're going to go for. You'll say Enceladus.

Yes. The Fountains of Enceladus. These fascinate me.

I want to know about the rings.

I want to know how long lived Saturn's rings are.

I want to know how long a day lasts on Saturn.

We still don't know exactly what the rotation rate of Saturn is.

-But you've got a probe orbiting it.

-I know.

But because it's not a solid surface

-and there isn't something on the surface that we can follow around...

-No Greenwich Meridian.

The observations we make in the magnetic field shows

it's around 10.7 hours, but if you're in the northern hemisphere,

it's different to when you're in the southern hemisphere.

That's why the end of mission when we get really close in will answer those questions.

It's a fundamental thing. How fast Saturn rotates determines how we map features on it.

And we don't know it. You can save your embarrassment by discovering that, what about you?

The question I'd like to have answered is why is the great red spot the colour red.

We don't know what the chemical is that causes it to be red in colour.

I hope that Juice will have the answer.

We've certainly learnt a great deal from the probes.

There's much more to be learned. I suspect that in ten years,

we'll have altered our ideas quite considerably.

Thank you all very much.

Now to Selsey Beach, where Pete and Paul are going to tell us something to look forward to.

-We've come down to this incredibly bleak beach...

-It is a bit!

..to talk about the things we can see in the night sky

over the next couple of months. There are some interesting things.

There are nice gentle things which are easy to see.

If the clouds were out of the way and it was a bit later at night,

after the sun had gone down, this is the season where you can see

a phenomena known as noctilucent clouds.

-Have you ever seen them?

-I haven't.

I know they can get very bright, very powerful.

We ought to explain what they are.

They're basically really high altitude clouds,

much higher than normal clouds we've got up here.

In the summer months, going through from late May into early August,

as the sun goes below the horizon, there's a period when the light

from the sun can't illuminate these clouds.

But if the sky is clear and you've got noctilucent clouds there,

they're high enough to be able to reflect sunlight.

Even though the sun is below the horizon, the clouds are shining away

at night, which is why they're called night shining clouds.

That's what noctilucent means.

-From what I've seen, they can change as well.

-They are amazing.

I've seen loads of noctilucent clouds here.

They sort of glow with an eerie electric blue.

That's the best way of describing them.

They look like a sort of network, a fine detailed network of clouds.

The way to look for them is to wait for the sun to go down,

a couple of hours after sunset, look in the north-west and if you can

see some glowy clouds, keep an eye on them, they could be noctilucent.

Also in the morning, a few hours before the sun comes up in the north-east.

If you get a really bright display, as we have had a few years back,

they will persist all the way through the night.

They're on the edge of the twilight glow you can see to the north.

-I'll hopefully get to see some this season.

-Another thing is they're very photogenic.

There are lots of beautiful photos to see on our Flickr site.

If you don't know the address, you can go on to:

The details are on there.

If you get any photos of them, and they could occur at any time

from late May through to early August, then do send them in.

We also have another interesting event on July 15th.

This is the occultation of Jupiter by the moon. It's not visible everywhere though.

This is actually quite an interesting event.

Jupiter will pass really close to the northern edge of the moon.

Right down in the south-east is the best view.

As you move up the country, you start to see less covering Jupiter.

In the Midlands, it's what's known as a grazing occultation.

Jupiter will appear to just pass over the top.

You can catch Jupiter passing the mountains and valleys on the edge of the moon.

That would make a lovely shot.

Start observing from about 2:30 BST onwards.

I hope it's a lot warmer than it is now. It can't be cloudy for all of these events.

-Hope we get something interesting.

-Definitely.

Let's begin our News Notes with Mars.

And there's an amazing probe, Opportunity, starting up again.

It's had eight years on the surface of Mars, but for the Martian winter, it's been stationary.

There isn't enough solar power in northern winter to give it enough power to drive its wheels.

But it's now started moving again.

It'll continue its journey around the rim of Endeavour Crater,

which is a much larger crater than it's been to before.

And the terrain there is much older. That's why it's there.

It did this massive trek across the surface to get to this point,

so we could read off billions of years of Martian history.

Before it went into its shutdown, it found a place

called Homestake, which had this bright material on the surface.

Turned out to be gypsum, which we know was deposited in reasonably warm water.

This was a lake or a sea, probably a nice temperature to go swimming in.

We now know that this was last underwater billions of years ago.

We're really getting to ancient Martian history.

Next, in the long term, Opportunity will continue its exploration

of the crater, working its way around the edge. Probably too steep to go in at any point.

Its immediate objective is more of this gypsum that's nearby.

We can see if Homestake was unusual or whether we need to go elsewhere.

How long will it last? We still don't know.

We come to Vesta, the brightest of the four largest asteroids.

Visited at the minute by the Dawn spacecraft,

which has just been given a few extra months at Vesta

to finish exploring this wonderful little world.

There's some fabulous movies that have been put together.

These are computer animations but with real data from Dawn.

-They're spectacular.

-They're showing us the grooves around Vesta.

We're not sure how they were created. Something to do with its violent past.

It's clear from the shape, it's got an enormous impact basin near its south pole.

We know that impact basin is relatively young,

a couple of billion years.

And mapping the surface of Vesta.

Its southern hemisphere is different to its northern hemisphere.

Dawn is going to be there until August this year,

before it moves on its way to Ceres.

-The most famous feature that Dawn's seen so far is the Snowman.

-Oh, yes!

This is over the middle of those craters that make up the Snowman.

This gives you a real sense of the terrain of Vesta,

what it would be like to be wandering across the surface.

-I'd love to try!

-We have to finish News Notes with at least one beautiful picture.

My favourite this month is from the European Southern Observatory

at La Silla in Chile.

This image of Centaurus A. A nearby active galaxy.

You can see the dust disc warped in the centre.

And then the galaxy extending out

and it's just an absolutely stunning image.

Centaurus A one of the most fascinating galaxies in our local neighbourhood.

It's 13 million light years away.

It's got a massive black hole in its centre with jets coming out of it.

In the top left, you can see some filaments of gas

which are linked to those jets of material

we see normally in X rays and radio waves.

Centaurus A in the past has swallowed up another galaxy.

It's been a cannibal.

That's what the warped disc in the centre is,

the remains of this smaller galaxy that got swallowed up.

-Pity we can't see it from here.

-Yes, but we can enjoy the image.

We can do. And here it is.

There's so much we're learning.

Chris and Chris, thank you very much.

Next month, we're going to talk about the inner solar system and of course the Transit of Venus.

Until then, good night.

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