How the Universe Works - Eleventh Season

Orbiting the magnificent ringed planet, Saturn,

are a series of extraordinary moons.

The closer that we look,

the more that we see its moons are like worlds of their own...

So dynamic, so Earth-like.

Almost a billion miles from the Sun,

these icy worlds could be home for Life 2.0.

The moons of Saturn offer possibly the best

chance of finding extraterrestrial life

in our solar system.

With each new mission, we get closer

to unraveling the mysteries of Saturn's moons.

October 2019.

Astronomers discover 20 new moons

orbiting the gas giant, Saturn.

These tiny, three-mile-wide objects

bring the ringed planet's moon count to over 80,

the most of any planet in our solar system.

You hate to play favorites, but I'm gonna say it...

Saturn is my favorite planetary system.

It is unbelievably beautiful, with this incredible system of

rings and moons,

and there's a lot of mystery kind of all bound up in there.

The Voyager spacecraft gave us our

first close look at Saturn and its rings.

Two decades later, Cassini got us even closer

to many of Saturn's moons.

There's Prometheus, Pandora, and Atlas.

Its largest moon, Titan, is a moon that's shrouded

in mystery.

There's Mimas, that's fairly small,

and then Tethys and Dione are a bit larger.

There are a pair of moons... Janus and Epimetheus...

That were perhaps one moon in the past.

Iapetus, half of it's bright white.

The other half of it is sort of as

dark as coal, sort of yin and yang.

Each of the moons of Saturn

had remarkable stories to tell.

In 2005, Cassini discovered that

one moon's story was particularly exciting.

Yeah, Enceladus.

Enceladus is one of Saturn's wee little moons.

It's about 300 miles across... For scale,

it's roughly the size of Colorado.

The spacecraft's cameras spot plumes of

water vapor shooting out from Enceladus

at 800 miles an hour.

Three times as powerful than

all the hot springs in Yellowstone.

The discovery of geysers gushing out of tiny,

little Enceladus that should have been cold and dead,

completely changed our view of what that moon exactly was.

It's alive. That moon is alive.

I'd like to be standing there on the surface of Enceladus to

see with the... this water vapor

and ice crystals booming out of the surface

at supersonic speeds.

Cassini's sensors probe deep beneath

the frozen surface of Enceladus,

detecting hints of a rocky core

and something else even more remarkable.

Underneath that thick layer of ice,

there is liquid water ocean.

The measurements suggest his is a huge part of

Enceladus's interior volume,

about six miles deep, because it was making Enceladus

wobble in its orbit.

Imagine putting liquid inside a ball and rolling it.

You see the natural wobble of

the ball as the liquid sloshes around.

Giant liquid oceans on an alien world,

opening up exciting new possibilities.

Where you find water, you could possibly find life.

If you had asked me 20 years ago where there might be life

in the solar system besides Earth,

I think Saturn's moons would have been the last place

I would have picked.

But against all odds, it's looking like this tiny icy

moon orbiting Saturn

nearly a billion miles from the Sun may be one of

the best places to look for life.

July 2021.

A new study reexamines Cassini's plume data

and finds huge quantities of methane.

This large amount can't be

explained by just geochemical processes.

The methane might be from primordial organic matter

breaking down in Enceladus's oceans,

or even processes we've never seen before.

But it could be that

living microorganisms helped generate the methane,

just like they do on Earth.

Enceladus might actually look a lot like early Earth in its

deepest oceans, when life was first arising,

because we know that there are some chemical pathways that are

likely occurring on Enceladus that happened on Earth.

These chemical pathways start with

hot, hydrothermal vents on Earth's

cold sea floor, releasing important life-giving chemicals

into the oceans.

Having hydrothermal vents are a real

boon to the evolution of life.

These are cracks in the Earth's crust, where

hot material can then spew out into the ocean.

And that's the energy

that life needs to be able to form,

and then water so everything is present, and things

are able to just grab all these resources and energy

and just start to evolve.

On Earth, hydrothermal vents produce methane,

but only in small amounts.

Microbial life

living around the vents makes the rest.

Maybe microorganisms do the same

at the bottom of Enceladus's deep oceans.

Hydrothermal vents on Enceladus could offer

the perfect location for chemistry

becoming biochemistry becoming life.

Hydrothermal vents normally require

heat from a hot core.

So what's going on inside Enceladus?

This is an icy moon out there in the cold outer solar system.

Where is all this heat coming from?

Cassini spotted Enceladus's plumes

shooting out from parallel cracks

in the surface, called tiger stripes.

The cracks are a clue to the origin of the geysers

and the energy that powers them.

We look to the orbit of Enceladus itself.

It's not in a perfectly circular orbit

around the planet.

It's on a slightly elliptical orbit, and that means that

the tidal forces acting on the moon change over time.

It's a little bit like the forces on a rubber ball.

When the moon is closer to the planet, it's stretched out,

and when the moon is farther from the planet,

it's relaxed back a little bit, so you're gonna squeeze

and deform and squish the body of

that moon over time, which is gonna heat its interior.

The warm, rocky core heats up the ocean,

which both powers the geysers as they burst

through the surface

and creates conditions that could support life.

We see the energy source kicking the water

out of the Enceladus subsurface.

You combine that energy source

and liquid water, that harkens to putting

us on the same path that early life

may have taken here on the Earth.

And if that's the case,

there could be little beasties swimming underneath the surface

of one of Saturn's moons.

Saturn's squeezing of Enceladus may

have transformed it into a living world,

but other moons weren't as lucky.

They've been torn apart in vicious fights

to the death.

There are a huge variety of moons orbiting Saturn,

from Titan, a moon larger than the planet Mercury,

to objects about the size of a sports stadium.

There must be something dramatic that happened

to create a system

that's so complicated and changing

before our very eyes.

To understand such a marked difference in size,

scientists look for clues in the moon's orbits around

Saturn itself.

Most of the moons of that system orbit in the same direction.

That's obviously not a coincidence.

That's motion left over from the formation

of our solar system.

This suggests the moons formed around

the same time as Saturn did.

4.6 billion years ago,

the ringless gas giant grows from gas,

rock, and ice in the protoplanetary disk,

along with a family of moons.

This origin story works for most of Saturn's moons,

but not for the recently discovered objects orbiting

in the opposite direction of the planet's rotation.

If there's a moon orbiting in the other direction,

it couldn't have formed with the planet.

It must have come from somewhere else.

Saturn captured these moons.

But from where?

We think there was a huge upheaval in the solar system

over four billion years ago,

where the giant planets

went from a close and compact configuration, started

having interactions with each other,

moved each other around to end up into the orbits

that they find today.

During that process, a lot of smaller bodies,

like asteroids from the distant part

of the solar system got scattered

every which direction.

During this ancient upheaval,

Saturn grabs some of the scattered objects.

Many bodies now crowd the region around the planet,