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00:00There are many worlds within our solar system.
00:04Most reside beyond the asteroid belt.
00:08These are the moons of the gas giants of the solar system,
00:12each a unique and mysterious world of its own.
00:15Some have oceans of water, geysers of sulfur, or atmospheres of plastic.
00:21Some are just now being seen at the outer rim of our solar system.
00:26All are worthy of much more scrutiny.
01:30Other probes have made flybys of the system en route to other destinations.
01:34Some of these return fascinating data on the Jovian moons.
01:38Jupiter, the largest planet in our solar system, has, as far as can be ascertained, 67 orbiting satellites.
01:52Most of them are odd-shaped rocky masses, probably asteroids like Amalthea, trapped in the massive gravitational field of the planet.
02:02However, there are four major satellites of Jupiter, each large and dense enough to form spherical bodies.
02:20These are called the Galilean moons, named after the great Italian scientist and astronomer Galileo Galilei, who discovered them in 1610.
02:31Io is the smallest of the Jovian moons, though somewhat larger than our own moon, and closest to orbit Jupiter.
02:44The intense gravitational effects causes the violent and active nature of the moon.
02:56It has over 400 volcanoes, lava flows and plumes of sulfur, 300 kilometers above the surface.
03:03The most dense of the four moons, Io is also the driest.
03:11Io is thought to be composed of mainly silicate rock, with a molten core of iron or iron sulfide.
03:18Most of the surface is composed of extensive planes, coated with sulfur and sulfur dioxide frost.
03:29The surface is geologically young, which accounts for the lack of impact cratering.
03:34Unlike all the other planetary bodies, these craters have been covered over by volcanic activities.
03:40Numerous active volcanoes also eject material high above the moon and into orbit around Jupiter.
03:50The internal energy for this overactive moon is due to gravitational tidal forces between Jupiter and the other moons orbiting farther out from Io.
04:01Just 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.
04:17It also has active geysers ejecting material into space.
04:22So how do we think we know that Europa's ocean exists?
04:33Well, it's a combination of using telescopes on the ground and having spacecraft that have flown by Europa
04:40and collected data about the surface, about the interior structure, and about the magnetic field around Europa.
04:47And the combination of those data sets leads us to a high degree of confidence that this global liquid water H2O ocean is there today.
04:56And it's been there for much of the history of the solar system.
04:59And here's where Europa is a real game changer.
05:02It is far, far out from the sun.
05:06And yet it's got this liquid water ocean.
05:09And the reason that Europa has liquid water is because it's orbiting Jupiter.
05:14And the tidal tug and pull causes Europa to flex up and down.
05:19And 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.
05:31Along with helping maintain liquid water, we think that tidal energy may also allow that ocean to interact with rocks on Europa's seafloor.
05:41And 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.
05:50Europa 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.
06:09And we know that on Earth, everywhere that there's water, we find life.
06:16So could Europa have the ingredients to support life?
06:20We might be actually looking at a body that is presently alive, presently active, and presently undergoing its geology.
06:28There is too much evidence right now lying around on the surface, the red stuff, that suggests that something's going on there.
06:35Is that an environment that is habitable for any sort of life form?
06:40By golly, we really have got to go back and figure that out.
06:43We have designed the Europa mission to take a spacecraft and its set of instruments all the way from planet Earth to Jupiter.
06:51Previous mission concepts were for a spacecraft that would orbit Europa.
06:56But Europa is bathed in radiation from Jupiter.
07:00Any mission that goes in the vicinity of Europa is cooked pretty quickly.
07:04Instead, we're looking at a mission that will orbit Jupiter, make close flybys of Europa, and then zip out of the high radiation region.
07:12This allows us to have a mission that's many years long, and to collect and transmit lots and lots of data.
07:19As Europa orbits Jupiter, it flexes.
07:22And we could measure the gravitational change of Europa by encountering Europa at different points in its orbit.
07:30On a typical flyby, we would turn on our remote sensing instruments, we would image the surface,
07:36we would interrogate the surface with spectroscopy, and we would do the same thing on the way out.
07:40And we would essentially rinse and repeat and do this many, many times until we understand Europa globally.
07:50Images from the Hubble Space Telescope tell us that Europa might be emitting plumes of water high into space.
07:57If so, a spacecraft could fly through those plumes and sample it directly to understand the composition of Europa's interior.
08:06If it does have the ability to harbor life, how does that work exactly?
08:10We'll have enough instrumentation to really pinpoint exactly how the mechanisms would work for replenishing the nutrients in a subsurface ocean.
08:19Europa is so important because we want to understand, are we alone in the cosmos?
08:26If there is life in Europa, it almost certainly was completely independent from the origin of life on Earth.
08:34And for the first time in the history of humanity, we have the tools and technology and capability to potentially answer this question.
08:46And we know where to go to find it.
08:50Jupiter's ocean world, Europa.
08:53The Europa Clipper mission has passed preliminary development and strategy proposals and acquired further funding.
09:09The European Space Agency has been invited to develop an additional probe to ride along with the Clipper,
09:16as with the Cassini Huygens mission, and either land or impact on the Moon's surface.
09:23The nominal Europa Clipper mission would perform 45 flybys of Europa at altitudes varying from 2700 to 25 kilometers.
09:34A proposed launch window would be in 2025.
09:37If launched with NASA's new SLS heavy lift rocket system, the probe would take less than two years to reach Jupiter.
09:45Otherwise, it would be a six and a half year flight.
09:56The largest Moon in the solar system, and another icy world, is Ganymede.
10:01Composed of silicate rock and water ice, the surface is heavily pockmarked by impact craters and regions of tectonic movement.
10:10The Moon has a thin atmosphere of oxygen and possibly ozone and atomic hydrogen.
10:16The Moon has a liquid iron-rich outer core and an internal ocean with possibly more water than Earth's oceans.
10:24Most recent modelling suggests the interior may be layers of water and ice, like a club sandwich.
10:31Ganymede is also the only Moon known to have a magnetic field.
10:36However, it is embedded within the powerful Jupiter magnetic field and overwhelmed.
10:42But there are indications of auroral activity on the Moon.
10:46Ganymede is also the final target for the Jupiter Icy Moon Explorer, or JUICE, the ESA-designated mission to three of the Jovian moons.
11:01It will be launched in 2022 from Europe's spaceport in Kourou, French Guiana, on an Ariane 5, arriving at Jupiter in 2030,
11:10to spend at least three years making detailed observations.
11:18It will visit Callisto, the most heavily crated object in the solar system, and will twice fly by Europa.
11:29Callisto is the fourth and most distant of the Jovian moons from Jupiter, and outside the main radiation belt of that planet.
11:38Unlike its sister moons, Callisto has a very thin atmosphere of carbon dioxide and molecular oxygen, and low radiation exposure.
11:48Callisto is composed of silicate rock and water ice, and may also harbour a subsurface ocean.
11:55It is considered the most environmentally acceptable location for a manned base in the future.
12:08Saturn has 62 confirmed orbital satellites, many less than 50 km in diameter.
12:19The bulk of the larger spherical moons are predominantly water ice and a small amount of rock.
12:26They include Mimas, Enceladus, Thetis, Dione, and Rhea.
12:37Enceladus is covered in ice with a subsurface ocean at the southern pole.
12:44Geologically active in the southern region, geysers have been observed.
12:49This would be from tidal heating and orbital resonance with Dione and Rhea,
12:54and could contain a liquid ocean heated by internal radioactive decay.
12:59However, the prize of the Saturnian system is undoubtedly Titan.
13:12Titan is the only moon with a dense atmosphere, and other than Earth, the only body to have stable bodies of surface liquid.
13:20It is larger than both the planet Mercury and our own moon.
13:24Cassini deposited the probe Huygens on its surface in 2005.
13:29Titan is Saturn's largest moon.
13:34It's actually the second largest moon in the solar system.
13:37And it's the only moon in the solar system that has a large and substantial atmosphere.
13:41And that atmosphere in some respects is really similar to that of the Earth, being composed mainly of nitrogen.
13:45But in other respects it's really different.
13:47It has methane as its second most abundant gas,
13:50and that takes the same role as water vapour in the Earth's atmosphere.
13:53It evaporates from the surface, it forms clouds, and then rains down again,
13:57and in fact forms lakes that we see at Titan's North Pole,
14:00including ethane and propane and all sorts of complex chemicals.
14:03We also see these vast dune fields of the equator,
14:06which are not made of silicates as they are on the Earth,
14:09but actually made of organic substances, essentially plastics,
14:12which have actually sedimented from the atmosphere
14:15and are being blown around into dune fields,
14:17the same as we'd see on a desert on the Earth.
14:28And through this we can detect which molecules are in the atmosphere.
14:31We see all the molecules that were previously discovered by Voyager.
14:34But we're also able to look for new molecules,
14:36and in fact buried within the signatures of these more abundant molecular species,
14:41we saw a very small spike, which was due to a new species which had not been seen before.
14:46In fact this was propylene.
14:49So the discovery of propylene on Titan is really exciting.
14:52First of all, it completes this chemical family where we have this missing link,
14:56dating 32 years back to Voyager.
14:59But also it shows that there's much more there still in Titan's atmosphere to be discovered.
15:03Some people think that Titan is similar to the prebiotic Earth long ago
15:08when the molecules were forming the basis of life.
15:10And we don't know what we're going to find on Titan if we send back further spacecraft
15:14with new instruments, more sensitive instruments,
15:16if some of the molecules on Titan could be similar to the basis of life on Earth.
15:20NASA is preparing a new probe to follow in Cassini's footsteps.
15:24It is called the Titan-Saturn System Mission.
15:28Cassini was able to look at the lakes,
15:31get a sense of the coarse composition of the lakes,
15:35but nothing about the organic molecules that are dissolved in the lakes.
15:39The Titan-Saturn System Mission is a three-in-one mission with an orbiter for Titan,
15:44a balloon that will float through Titan's atmosphere,
15:47and a lander that will splash down on one of the northern lakes of Titan.
15:51This mission will actually go into a lake, sample the liquid directly,
15:56see what the organic molecules are that are present.
16:00The Titan-Saturn System Mission also will go to Enceladus,
16:04the tinier moon, a thousand times smaller than Titan,
16:08which has volcanoes, geysers essentially,
16:11that are spewing material from the inside of this moon outward.
16:15And it's a chance to see whether there might be molecules
16:18that would indicate that life has actually formed within the source region of these geysers.
16:24These geysers have water ice and we strongly suspect that there's liquid water
16:28in the region that these geysers are coming from.
16:31We know there are organic molecules there because they've been measured by Cassini.
16:35The ability to follow this up quickly is essential because with Cassini Huygens,
16:41we have now trained a generation of scientists who are ready to take a new generation of instruments
16:47and capabilities back to Titan and Enceladus
16:50and really answer the questions that Cassini Huygens has left for us.
16:55And that continuity of knowledge and of enthusiasm is essential
17:01and very difficult to maintain in the outer solar system because trip times are so long.
17:06The Titan-Saturn System mission really is Jules Verne realized.
17:11It's a kind of planetary exploration that we have never ever done before anywhere else in the solar system
17:16and can only be done on Titan.
17:19This mission will touch the human heart in terms of the way it's exploring this fascinating world.
17:27It will be floating on the surface of a lake.
17:30It will be floating through the atmosphere.
17:32It will be revealing the entire surface from orbit at the same time.
17:37As we think of exploration, of unveiling a new world,
17:41it's exploration in the true sense of the word.
17:44The planet Uranus has 27 known moons, grouped in three categories.
18:0213 inner moons, 5 major moons and 9 irregulars.
18:07Only Voyager 2 has passed by these worlds.
18:12There remains much to learn.
18:14The major moons in order from the planet are Miranda, Ariel, Umbriel, Titania and Oberon.
18:23Four of these moons have known internal processes such as vulcanism and surface canyon formation.
18:30Miranda 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.
18:39Strangely, it also has the tallest cliffs in the solar system.
18:44Thought to consist of equal parts of rock and ice, Ariel's surface terrain, probably of ice, is crosscut with canyons, scarps and ridges.
18:53Umbriel is again thought to consist of rock and ice.
19:00Its surface is the darkest of the moons and heavily cratered.
19:04The surface seems to have gone through some form of surface heating that destroyed its very early features.
19:11Titania is the largest of Uranus's moons.
19:16Similar in composition, heavy cratering has been obscured by changes to the surface through some heating event like its sister Umbriel.
19:25Titania may have a tenuous atmosphere as carbon dioxide and water ice have been detected on its surface.
19:34Oberon, the outermost of the spherical moons, seems similar to the others.
19:39Ice and rock and heavily cratered.
19:42The surface has numerous scarps and graven from crustal movement.
19:47There are currently no plans to revisit these worlds.
19:55Neptune has 14 known moons, categorized into two groups, the regulars and the irregulars.
20:02The inner seven moons orbit normally.
20:05The remaining half, including its largest moon, Triton, orbit in either an eccentric, inclined or retrograde motion.
20:14Triton orbits in the opposite direction to Neptune's spin.
20:18Scientists believe it was probably captured by Neptune's gravity in the early days of the solar system.
20:25Triton has an atmosphere that forms clouds and haze and is the only moon closely observed by Voyager on its flyby of the system.
20:37However, Neptune plays a very important role at the edge of the solar system.
20:44The planets form from a disk of dust surrounding our sun billions of years ago.
20:51Remnants of this disk still remain.
20:54The rocky asteroid belt influenced by Jupiter and the icy debris cloud beyond Neptune.
21:00Neptune creates a ring structure in the dust cloud which features a gap where the planet itself resides.
21:05And 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.
21:14The 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.
21:22In effect, we can go back in time and see how the distant view of the solar system may have changed.
21:27When we included collisions between dust particles, we were really amazed by what we saw.
21:33Dust collisions change Neptune's gravitational imprint.
21:37The gap in the ring structure disappears.
21:42Over billions of years, Neptune shepherds the dust cloud into an outer ring to what is now called the Kuiper Belt.
21:51The New Horizons spacecraft is exploring this region with its first flyby of the enigmatic Pluto and its moon Charon.
22:02Charon is the largest of Pluto's five moons.
22:05The other four orbit in erratic motion around the Pluto-Charon pair.
22:11Nix and Hydra are both odd-shaped, contributing to their erratic orbital motions.
22:19This is Hydra, taken by New Horizons from a distance of nearly 650,000 kilometers, revealing its irregular shape.
22:32Pluto was the first of these trans-Neptunian objects detected and first thought to be a ninth planet.
22:38And then Pluto was this kind of, you know, odd guy out.
22:43It was this little object at the edge of the solar system.
22:47And then when we found all these other Kuiper Belt objects, this is kind of almost a third type of object.
22:53So, 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,
23:04and understand what outer parts of the solar system are all about.
23:09Pluto is the first of the Kuiper Belt objects, or KBOs, to be seen up close.
23:15There are many other KBOs, or dwarf planets, awaiting detailed scrutiny,
23:20such as Eris, almost the size of Mercury, and Quawar, the first KBO discovered.
23:27The most eccentric orbit belongs to Senda, which has an elliptical orbit of 11,000 years,
23:34taking it to the icy Oort cloud at the edge of the solar system.
23:39The Oort cloud will one day become the new frontier.
23:57of the Kuiper Belt against the solar system.