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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.

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.

Several other probes have
made flybys of the system

en route to other destinations.

Some of these return fascinating
data on the Jovian moons.

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.

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.

Io is the smallest of the Jovian moons,

though somewhat larger than our own moon

and closest to orbit Jupiter.

The intense gravitational effect

causes the violent and
active nature of the moon.

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

300 kilometers above the surface.

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.

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.

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.

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?

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.

We have
designed a Europic mission

to take a spacecraft
and a set of instruments

all the way from planet Earth to Jupiter.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

However, the prize of
the Saturnian system,

is undoubtedly, Titan.

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.

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.

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.

NASA is preparing a new probe

to follow in Cassini's footsteps.

It is called the Titan
Saturn System Mission.

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.

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.

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.

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.

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.

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.

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.

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.

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.