Original subtitles

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.

What is Jupiter? Currently en route to the Jupiter system

is the scientific probe Juno. It will be the first orbiter

mission to Jupiter since the troubled Galileo spacecraft in

2003. Its 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. 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.

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.

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

planes, coated with sulfur and sulfur dioxide frost. Most of

the surface is composed of extensive planes, 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. Unlike all the

other planetary bodies, these craters have been covered over

by volcanic activities.

Unlike all the other planetary bodies, these craters

have been covered over by volcanic activities. 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 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 seafloor 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 its surface and 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 suggests 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 the Europa mission to take a spacecraft and

its 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're 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 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

replenishing 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 have nowhere 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 would 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 pockmarked 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 IC Moon

Explorer, or JUS, 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 to 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.

Saturn has 62 confirmed orbital satellites, many less than 50 kilometers in

the solar system. In addition to Saturn, Saturn is also

known to have a small amount of rock. They include Mimas,

Enceladas, Thetis, Dione, Andrea.

Enceladas 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 Andrea 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 its second most abundant gas, and that takes

the same role as water vapor in the Earth's atmosphere. It

evaporates from the surface, it 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 is really exciting. First of all, it

completes this chemical family where we have 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 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, as Jules Verne realized, it's a kind of planetary

exploration that we have never ever done before anywhere

else in

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. As

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 cross-cut

with canyons, scarps and ridges.

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

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 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 changed 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 an

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. This is the largest of Pluto's five moons.

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, you know, 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 kind of almost a third type of object. So for the first

time ever, we'll 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 Quahua, the first KBO

discovered. The most eccentric orbit belongs to Senda, which

has an elliptical orbit of 11,000 years, taking it to

the icy Oort cloud at the edge of the solar system.