Original subtitles

- [Man 1] There are many worlds within our solar system.

Most reside beyond the asteroid belt.

These are the moons of the gas giants

of the solar system.

Each a unique and mysterious world of its own.

Some have oceans of water,

geysers of sulfur,

or atmospheres of plastic.

Some are just now being seen at the outer rim

of our solar system,

all are worthy of much more scrutiny.

(dramatic music)

Currently, our route to the Jupiter system

is the scientific probe, Juno.

It will be the first orbiter mission to Jupiter

since the traveled Galileo spacecraft in 2003.

It's task,

to establish a highly elliptical polar orbit,

and study Jupiter in the greatest detail so far.

(futuristic music)

Several other probes have made flybys of the system

en route to other destinations.

Some of these return fascinating data on the Jovian moons.

(futuristic music)

Jupiter, the largest planet in our solar system,

has, as far as can be ascertained, 67 orbiting satellites.

Most of them are odd-shaped, rocky masses,

probably asteroids like Amalthea,

trapped in a massive gravitational field of the planet.

(futuristic music)

However, there are four major satellites of Jupiter,

each large and dense enough to form spherical bodies.

These are called the Galilean Moons,

named after the great Italian scientist and astronomer,

Galileo Galilei, who discovered them in 1610.

(futuristic music)

Io is the smallest of the Jovian moons,

though somewhat larger than our own moon

and closest to orbit Jupiter.

(futuristic music)

The intense gravitational effect

causes the violent and active nature of the moon.

(futuristic music)

It has over 400 volcanoes, lava flows and plumes of sulfur,

300 kilometers above the surface.

(futuristic music)

The most dense of the four moons, Io is also the driest.

Io is thought to be composed of mainly silicate rock

with a molten core of iron or iron sulfide.

Most of the surface is composed of extensive plains,

coated with sulfur and sulfur dioxide frost.

The surface is geologically young,

which accounts for the lack of impact cratering.

Unlike all the other planetary bodies,

these craters have been covered over by volcanic activities.

Numerous active volcanoes also eject material

high above the moon and into orbit around Jupiter.

The internal energy for this overactive moon

is due to gravitational tidal forces between Jupiter

and the other moons orbiting farther out from Io.

(futuristic music)

Just slightly smaller than our own moon,

Europa has an icy crust covering what is believed to be

a salty global ocean,

capable of sustaining indigenous life.

It also has active geysers ejecting material into space.

(futuristic music)

- [Man 2] So how do we think we know

that Europa's ocean exists?

Well, it's a combination of using telescopes on the ground,

and having spacecraft that have flown by Europa

and collected data about the surface,

about the interior structure,

and about the magnetic field around Europa.

And the combination of those data sets

leads us to a high degree of confidence

that this global liquid water, or H2O, ocean is there today,

and it's been there for much of the history

of the solar system.

And here's where Europa is a real game-changer.

It is far, far out from the sun,

and yet it's got this liquid water ocean,

and the reason that Europa has liquid water,

is because it's orbiting Jupiter,

and the tidal tug and pull causes Europa

to flex up and down,

and all that tidal energy turns into mechanical energy,

which turns into friction and heat

that helps maintain this liquid water ocean

beneath an icy shell.

Along with helping maintain liquid water,

we think that tidal energy may also allow that ocean

to interact with rocks on Europa's sea floor,

and it may even give rise

to things like hydrothermal vents,

which could help provide

not just the building blocks for life, but also,

the energy for life.

(dramatic music)

- [Man 3] Europa is the most likely place to find life

in our solar system today,

because we think there's a liquid water ocean

beneath it's surface.

Now, we know, that on Earth,

everywhere that there's water, we find life.

So, could Europa have the ingredients to support life?

- [Woman 1] We might be actually looking at a body

that is presently alive, presently active,

and presently undergoing its geology.

There is too much evidence, right now,

lying around on the surface, the red stuff,

that suggest that something's going on there.

Is that an environment that is habitable

for any sort of life form?

By golly, we really have got to go back

and figure that out.

- [Woman 2] We have designed a Europic mission

to take a spacecraft and a set of instruments

all the way from planet Earth to Jupiter.

- [Man 4] Previous mission concepts were for

a spacecraft that would orbit Europa.

But, Europa is bathed in radiation from Jupiter.

Any mission that goes in the vicinity of Europa

is cooked pretty quickly.

Instead, we were looking at a mission

that will orbit Jupiter,

make close flybys of Europa,

and then zip out of the high radiation region.

This allows us to have a mission that's many years long,

and to collect and transmit lots and lots of data.

As Europa orbits Jupiter, it flexes,

and we could measure the gravitational change of Europa

by encountering Europa at different points in its orbit.

On a typical flyby, we would turn on

our remote sensing instruments,

we would image the surface,

we would interrogate the surface with spectroscopy,

and we would do the same thing on the way out.

And we would, essentially, rinse and repeat,

and do this many, many times

until we understand Europa globally.

- [Man 1] Images from the Hubble Space Telescope tell us

that Europa might be emitting plumes of water

high into space.

If so, a spacecraft could fly through those plumes,

and sample it directly to understand the composition

of Europa's interior.

- [Woman 3] If it does have the ability to harbor life,

how does that work, exactly?

We'll have enough instrumentation to really pinpoint

exactly how the mechanisms would work

for replensihing the nutrients in a subsurface ocean.

- [Man 5] Europa is so important,

because we want to understand,

are we alone in the cosmos?

If there is life in Europa,

it almost certainly was completely independent

from the origin of life on Earth.

- [Man 6] And for the first time in the history of humanity,

we have the tools, and technology, and capability,

to potentially answer this question.

And, we know where to go to find it,

Jupiter's ocean world, Europa.

(rhythmic music)

- [Man 1] The Europa Clipper Mission

has passed preliminary development and strategy proposals,

and acquired further funding.

The European Space Agency has been invited to develop

an additional probe to ride along with the Clipper,

as with the Cassini-Huygens Mission,

and either land or impact on the moon's surface.

The nominal Europa Clipper Mission

would perform 45 flybys of Europa,

at altitudes varying from 2,700 to 25 kilometers.

A proposed launch window would be in 2025.

If launched with NASA's new SLS Heavy-Lift Rocket System,

the probe would take less than two years to reach Jupiter.

Otherwise, it will be a six and a half year flight.

(dramatic music)

The largest moon in the solar system,

and another icy world, is Ganymede.

Composed of silicate rock and water ice,

the surface is heavily pock-marked by impact craters

and regions of tectonic movement.

The moon has a thin atmosphere of oxygen,

and possibly, ozone and atomic hydrogen.

The moon has a liquid iron-rich outer core,

and an internal ocean,

with possibly more water than Earth's oceans.

Most recent modeling suggests the interior

may be layers of water and ice, like a club sandwich.

Ganymede is also the only moon

known to have a magnetic field.

However, it is embedded

within the powerful Jupiter magnetic field

and overwhelmed.

But, there are indications of auroral activity on the moon.

(futuristic music)

Ganymede is also the final target

for the Jupiter Icy Moon Explorer, or JUICE,

the ESA designated mission to three of the Jovian moons.

It will be launched in 2022,

from Europe's spaceport in Kourou, French Guiana,

on an Ariane 5, arriving at Jupiter in 2030,

will spend at least three years

making detailed observations.

It will visit Callisto,

the most heavily cratered object in the solar system,

and will twice fly by Europa.

(futuristic music)

Callisto is the fourth, and most distant,

of the Jovian moons from Jupiter,

and outside the main radiation belt of that planet.

Unlike its sister moons,

Callisto has a very thin atmosphere

of carbon dioxide and molecular oxygen,

and low radiation exposure.

Callisto is composed of silicate rock and water ice,

and may also harbor a subsurface ocean.

It is considered the most environmentally acceptable

location for a manned based in the future.

(dramatic music)

Saturn has 62 confirmed orbital satellites,

many less than 50 kilometers in diameter.

The bulk of the larger, spherical moons

are predominately water ice and a small amount of rock.

They include Mimas, Enceladus,

Tethys,

Dione and Rhea.

Enceladus is covered in ice,

with a subsurface ocean at the southern pole.

Geologically active in the southern region,

geysers have been observed.

This would be from tidal heating,

and orbital resonance with Dione and Rhea,

and could contain a liquid ocean,

heated by internal radioactive decay.

(futuristic music)

However, the prize of the Saturnian system,

is undoubtedly, Titan.

(futuristic music)

Titan is the only moon with a dense atmosphere,

and, other than Earth,

the only body to have stable bodies of surface liquid.

It is larger than both the planet Mercury

and our own moon.

Cassini deposited the probe Huygens on its surface in 2005.

(futuristic music)

- [Man 7] Titan is Saturn's largest moon,

it's actually the second largest moon in the solar system.

And it's the only moon in the solar system

that has a large and substantial atmosphere.

And that atmosphere, in some respects,

is really similar to that of the Earth,

being composed mainly of Nitrogen.

But, in other respects, it's really different,

it has methane as it's second most abundant gas,

and that takes the same role as water vapor

in the Earth's atmosphere.

It evaporates from the surface,

and forms clouds, and then rains down again.

And, in fact, forms lakes that we see at Titan's north pole,

including ethane and propane,

and all sorts of complex chemicals.

We also see these vast dune fields at the equator,

which are not made of silicates, as they are on the Earth,

but actually made of organic substances,

essentially plastics, which have actually sedimented

from the atmosphere,

and are being blown around into dune fields,

the same as we'd see on a desert on the Earth.

(ethereal music)

And through this, we can detect which molecules

are in the atmosphere.

We see all the molecules that were previously discovered

by Voyager.

But, we're also able to look for new molecules,

and, in fact, buried within the signatures

of these more abundant molecular species,

we saw a very small spike, which was due to a new species

which had not been seen before.

In fact, this was propylene.

So, the discovery of propylene on Titan was really exciting.

First of all, it completes this chemical family

who had this missing link,

dating 32 years back to Voyager.

But also, it shows that there's much more there, still,

in Titan's atmosphere to be discovered.

Some people think that Titan is similar

to the prebiotic Earth long ago,

when the molecules were forming the basis of life.

And we don't know what we're going to find on Titan,

if we send back further spacecraft,

with new instruments, more sensitive instruments,

if some of the molecules on Titan

could be similar to the basis of life on Earth.

- [Man 1] NASA is preparing a new probe

to follow in Cassini's footsteps.

It is called the Titan Saturn System Mission.

- [Man 8] Cassini was able to look at the lakes,

get a sense of the coarse composition of the lakes,

but nothing about the organic molecules

that are dissolved in the lakes.

The Titan Saturn System Mission is a three-in-one mission

with an orbiter for Titan,

a balloon that will float through Titan's atmosphere,

and a lander that will splash down

on one of the northern lakes of Titan.

This mission will actually go into a lake,

sample the liquid directly,

see what the organic molecules are that are present.

The Titan Saturn System Mission also will go to Enceladus,

the tinier moon, a thousand times smaller than Titan,

which has volcanoes, geysers, essentially,

that are spewing material

from the inside of this moon outward.

And it's a chance to see whether there might be molecules

that would indicate that life has actually formed

within the source region of these geysers.

These geysers have water ice,

and we strongly suspect that there's liquid water

in the region that these geysers are coming from.

We know that there are organic molecules there,

because they've been measured by Cassini.

The ability to follow this up quickly is essential,

because, with Cassini-Huygens,

we have now trained a generation of scientists

who are ready to take a new generation of instruments

and capabilities back to Titan and Enceladus.

And really answer the questions that Cassini-Huygens

has left for us.

And that continuity of knowledge, and of enthusiasm,

is essential and very difficult to maintain

in the outer solar system, because trip times are so long.

The Titan Saturn System Mission

really is Jules Verne realized.

It's a kind of planetary exploration

that we have never ever done before

anywhere else in the solar system,

and can only be done on Titan.

This mission will touch the human heart

in terms of the way it's exploring this fascinating world.

It will be floating on the surface of a lake,

it will be floating through the atmosphere,

it will be revealing the entire surface from orbit

at the same time.

Thus we think of exploration, of unveiling a new world.

It's exploration in the true sense of the word.

- [Man 1] The planet Uranus has 27 known moons,

grouped in three categories,

13 inner moons, five major moons, and nine irregulars.

Only Voyager 2 has passed by these worlds,

there remains much to learn.

The major moons, in order from the planet,

are Miranda, Ariel, Umbriel, Titania,

and Oberon.

Four of these moons have known internal processes,

such as vulcanism and surface canyon formation.

Miranda is the smallest of Uranus's round moons

and one of the smallest objects in the solar system

to be spherical under its own gravity.

Strangely, it also has the tallest cliffs

in the solar system.

Thought to consist of equal parts of rock and ice,

Ariel's surface terrain, probably of ice,

is crosscut with canyons, scarps, and ridges.

Umbriel, is, again, thought to consist of rock and ice.

It's surface is the darkest of the moons,

and heavily cratered.

The surface seems to have gone through some form

of surface heating that destroyed its very early features.

Titania is the largest of Uranus's moons.

Similar in composition,

heavy cratering has been obscured by changes to the surface

through some heating event, like its sister, Umbriel.

Titania may have a tenuous atmosphere,

as carbon dioxide and water ice have been detected

on its surface.

Oberon, the outermost of the spherical moons,

seems similar to the others,

ice, and rock, and heavily cratered.

The surface has numerous scarps and graben

from crustal movement.

There are currently no plans to revisit these worlds.

(futuristic music)

Neptune has 14 known moons, categorized into two groups,

the regulars and the irregulars.

The inner seven moons orbit normally,

the remaining half, including its largest moon, Triton,

orbit in either an eccentric, inclined or retrograde motion.

Triton orbits in the opposite direction to Neptune's spin.

Scientists believe it was probably captured

by Neptune's gravity in the early days of the solar system.

Triton has an atmosphere that forms clouds and haze,

and is the only moon closely observed by Voyager

on its flyby of the system.

(futuristic music)

However, Neptune plays a very important role

at the edge of the solar system.

The planets formed from a disk of dust

surrounding our sun billions of years ago.

Remnants of this disk still remain.

The rocky asteroid belt, influenced by Jupiter,

and the icy debris cloud beyond Neptune.

- [Man 9] Neptune creates a ring structure

in the dust cloud, which features a gap,

where the planet itself, resides.

And this gap should make it fairly easy to tell

where Neptune is from afar,

even at distances where the planet is too dim

to detect directly.

The supercomputer simulations

that Mark Kushner and I performed,

also allow us to see what the dust in the solar system

may have looked like when the solar system was much younger.

In effect, we can go back in time,

and see how the distant view of the solar system

may have changed.

When we included collisions between dust particles,

we were really amazed by what we saw.

Dust collisions change Neptune's gravitational imprint.

The gap in the ring structure disappears.

- [Man 1] Over billions of years,

Neptune shepherds the dust cloud into an outer ring,

to what is now called the Kuiper Belt.

The New Horizons spacecraft is exploring this region

with its first flyby of the enigmatic Pluto,

and its moon, Charon.

Charon is the largest of Pluto's five moons.

The other four orbit in erratic motion

around the Pluto-Charon pair.

Nix and Hydra are both odd-shaped,

contributing to their erratic orbital motions.

This is Hydra, taken by New Horizons

from a distance of nearly 650,000 kilometers,

revealing its irregular shape.

Pluto was the first of these

trans-Neptunian objects detected,

and first thought to be a ninth planet.

- [Woman 4] And then, Pluto was this kind of odd guy out.

It was this little object at the edge of the solar system,

and then when we found all these other Kuiper Belt objects,

this is almost a third type of object.

- [Man 10] So, for the first time ever,

we will be able to fly by a brand new object,

an object that's been forming for billions of years,

and understand what outer parts of the solar system

are all about.

- [Man 1] Pluto is the first of the Kuiper Belt objects,

or KBOs, to be seen up close.

There are many other KBOs, or dwarf planets,

awaiting detailed scrutiny,

such as Eris, almost the size of Mercury,

and Quaoar, the first KBO discovered.

The most eccentric orbit belongs to Sedna,

which has an elliptical orbit of 11,000 years,

taking it to the icy Oort Cloud

at the edge of the solar system.

The Oort Cloud will one day become the new frontier.

(mysterious music)