Space's Deepest Secrets

Across the world, astronomers are locked in a race.

They want to be the first to discover a moon

outside our solar system... A so-called exomoon.

But there's a problem... They can't find any.

What's weird about this is that

there's likely trillions of exomoons.

Astronomers have found thousands of planets

orbiting distant stars,

but none of them appear to have moons.

There have to be exomoons, of course there are exomoons.

Are they simply too hard to find,

or is our own solar system, which has many moons, unique?

Now a new generation of advanced telescopes hunts for clues.

Maybe we're gonna find something really, really strange.

Literally the first exomoon we find could be earthlike.

Who will make the first confirmed discovery

and solve the mystery of these missing moons?

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Earth's moon dominates the night sky.

Its immense gravity raises tides in the oceans,

and its 27-day passage around Earth

marks the months of the year.

But our planet isn't alone in having a moon.

A moon is defined in a number of ways...

One, it has to be smaller than its host planet,

and it has to circle its host planet.

If something does those two things, it's a moon.

There are more than 150 moons in our solar system,

each moon is different.

From violently volcanic Io in close orbit around Jupiter,

to Saturn’s largest moon, titan,

that conceals vast lakes of liquid methane and ethane.

Scientists expect alien planets in distant solar systems

to have moons, too.

They call these "exomoons."

The problem is, no matter how hard astronomers look,

they can't find them.

There could be up to a trillion exomoons in our galaxy alone,

and we have yet to discover one.

Scientists are desperate to make the first confirmed discovery

of an exomoon, not just to prove they exist,

but because many moons could be host

to something very special indeed... alien life.

Scientists now believe that the surfaces

and deep interiors of some moons

could be a better place to find liquid water

than the planets they surround.

These moons could provide the perfect conditions

for some form of life to have taken hold,

just like it did on the early Earth.

In our solar system, some of the most likely environments

for life are not on the planets, but they're on the moons.

In other star systems, why should it be any different?

Life on moons may be far more common than life on planets.

But moons are smaller than planets.

This makes them harder to detect.

So scientists are turning to evermore novel

and ingenious methods to track them down.

In the Netherlands, astronomer Matt Kenworthy

has recently made an incredible breakthrough.

He thinks he may have uncovered indirect evidence

of an exomoon 430 light-years from Earth.

I think it's very exciting,

because it's something which is brand-new,

and we don't know the answers yet.

Matt's discovery is based on an extraordinary observation.

To hunt down planets, astronomers look for tiny dips

in light as the planet passes in front of its host star.

Matt finds one of these dips,

but it's unlike anything he's seen before...

Something enormous is blocking light from the star.

We typically look at a signal for about six hours or so

whilst the planet blocks out

a small amount of light from the star.

This lasted much longer.

Instead of six hours, this lasted over two months.

And even stranger, in places the vast object

appears to let light through.

Instead of a nice, smooth curve,

you can see lots of rapid variation.

It's like somebody's

switching the star on and off very rapidly.

And even during individual nights,

you can see the star change brightness by as much as 50%.

Matt is convinced that this weird signal means one thing...

The object blocking the starlight

must be an alien planet with multiple rings like Saturn

but on a much larger scale.

Gaps in these rings would explain

why it's letting light through.

And it also hints at an extraordinary possibility.

Could there be exomoons hiding in the gaps?

Let's see if we can find Saturn.

Ah, okay, there we go.

I can see the rings.

Saturn's rings are made from trillions of icy particles.

But the gaps form when these particles collide

and stick together to create tiny moonlets.

As they sweep up more and more debris,

both the moonlets and the gaps grow bigger.

Scientists think that this is how most moons form

around newly born planets.

Young planets with rings

could be nothing more than gigantic moon factories.

The thing we know from our example of the solar system

is that rings and moons are related.

If you can find rings around a planet,

there's a very, very good chance there must be moons.

So look for the rings, and look for gaps in the rings.

Matt analyzes the flickering starlight

to work out what the rings of the alien planet

might look like.

What he finds is truly incredible.

At least 37 separate rings, 200 times larger than Saturn’s,

span over 110 million miles.

One of the gaps between the rings

is almost 2.5 million miles wide.

Matt suspects it could be home

to something never seen before...

a giant exomoon in the final stages of formation.

But to clear out a gap that big, just how large is it?

Matt uses computer simulations to find out.

Because we see this cleared gap in the ring system,

one possible interpretation

is that there is a moon forming right now,

and it's vacuuming up... It's using gravity to clear out

all the dust of that particular location in the ring system.

And how wide that ring gap is gives us a very good estimate

of how massive the moon is right at this moment.

And we worked out that it should be something

on the order of the size of Mars.

The biggest moons in our solar system

are Jupiter's Ganymede and Saturn’s titan,

but Matt's exomoon is at least four times as massive.

On the scale of a rocky planet.

His discovery is exciting,

but it rests on just one single observation.

Matt needs more data to say for sure that his giant,

Mars-sized exomoon is real.

The problem is, he has no idea when the alien-ringed planet

with its exomoon will pass in front of its star again.

It's a very large structure, and so it must take

a very long time to orbit.

So it wouldn't be too surprising

if it took anywhere between 10 to 20 years

for this thing to block the starlight again.

We've detected a giant ring system,

something hundreds of times the size of Saturn’s rings.

Have we indirectly detected the first exomoons?

Possibly.

While Matt waits for new data to win the exomoon race,

others are hot on his heels and hope to beat him to it.

In new Mexico, one scientist plans to find these moons

by listening to the night sky.

Scientists are in a race

to make the first confirmed discovery of an exomoon,

a moon outside our solar system that orbits an alien planet.

Astronomer Marialis Rosario-Franco

pioneers a remarkable new technique

to detect these moons.

Using a radio telescope like this one in new Mexico,

she attempts to tune in to their galactic broadcasts.

Radio telescopes detect radio waves,

a form of light that we can't see

but is the basis for radio communication.

We are at the long wavelength array

and what we have is about 200 antennas,

and together they make up a radio telescope.

Marialis believes that the geology of certain exomoons

may turn them into natural radio transmitters.

Discovering these could be as simple

as picking up their signal.

To prove it, she tunes in to a moon much closer to home.

So, what we're listening to right now,

you'll notice they sound like popping sounds.

This is the radio signal from Jupiter's moon, Io.

The two radio signals that Io makes are L- and s-bursts.

"L" stands for "long-burst," "S" stands for "short."

What we're listening to right now are s-bursts.

What turns a moon like Io into a radio transmitter?

The surprising answer?

Volcanoes.

Io is the most volcanically active world

in the solar system.

Its hundreds of volcanoes spew out vast amounts of gas.

Jupiter's powerful magnetic field charges and corrals

this gas into an enormous doughnut of electric fog

that surrounds the planet.

As Io orbits around Jupiter,

it interacts with this fog and Jupiter's magnetic field...

triggering the release of radio waves far out into space.

Jupiter has a strong magnetic field,

and that interacts with one of its moons, Io,

and that produces a tremendous amount of radio energy.

If other planets have magnetic fields

and they have moons like Io,

we might be able to detect that radio energy from them

without ever actually having seen the planet

or the moon themselves.

Planets like Jupiter are incredibly common in our galaxy,