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00:00In the cold, dark expanse of our solar system, beyond the asteroid belt, lie the giant planets.
00:11Some can be seen with the naked eye, others only glimpsed once by a passing probe.
00:19We are again sending cameras to the edge of the solar system to bring us new insights into the evolution of our worlds.
00:29We'll see you next time.
00:59Pioneer 10 and 11 made the first passage through the asteroid belt, leading the way for the venerable Voyager missions.
01:17These two probes made a grand tour of the outer solar system before slipping away into interstellar space.
01:33Jupiter, the first and greatest of the outer planets with its broiling sky, has had fleeting visits from other missions, like Ulysses, Galileo and Cassini, each adding to the mosaic of Jupiter and its violent atmosphere.
01:58My name is Amy Simon Miller and I study the atmospheres of the Jovian planets.
02:08Weather on Jupiter is confined to a rather thin layer, kind of high up in the atmosphere.
02:13So the tops of the clouds are what we're seeing when we look at Jupiter.
02:16One thing we're seeing in the southern part of the equatorial region is little V-shaped clouds, or chevrons, and we wanted to understand how those are moving in the atmosphere.
02:25What we think chevrons are are simply holes in the clouds.
02:28There are simply areas where we don't see any bright white clouds.
02:32The Cassini mission flew by Jupiter in the year 2000, and because it was a slow distant flyby, we got a lot of coverage of the planet over a long time period.
02:41So we were able to put those images together and make movies.
02:44Using these movies, we observed frosty waves that caused north-south meanders in a jet stream south of the equator.
02:50With new movies, we instead focused on hotspots.
02:54Hotspots are unique because we believe that there is a frosty wave similar to what we previously detected,
02:59but instead of this frosty wave moving north-south, it primarily moves up and down in the atmosphere.
03:05The downward portion of the wave pushes air down into warmer layers of the atmosphere.
03:09This causes any clouds that are embedded within the wave to evaporate and prevents further clouds from forming.
03:14So at any given time, there are approximately eight to ten hotspots in Jupiter's atmosphere that are spaced roughly evenly apart from one another.
03:22We believe that each of the downward portions of this frosty wave corresponds to the hotspots that we see on Jupiter.
03:28This new finding is exciting because it will allow us to re-examine the Galileo probe data,
03:33and allow us to better understand it and better place it in the context of Jupiter's overall global climate and atmosphere.
03:39The latest probe to be specifically aimed for Jupiter is Juno.
03:48Launched 2011, the probe will reach Jupiter after a five-year journey.
03:55Juno's goal is to investigate Jupiter's interior structure and magnetosphere,
04:03and help improve our understanding of the formation of the planet, and therefore the history of our solar system.
04:17Juno spins like a propeller, where the propeller's kind of facing the sun because they're all solar-powered.
04:23If you spin something, it stays spinning. It's like a gyroscope.
04:26We can use a spinning spacecraft to let each instrument get its turn to see Jupiter.
04:31We get to go very close to the planet, inside the radiation belts, instead of outside the radiation belt.
04:37We're in a polar orbit, so by small adjustments of the timing, we can map the entire planet.
04:42We can get repeated stripes at different longitudes as Jupiter spins underneath us.
04:47It does mean that Juno is going to see the polar regions to a greater extent than with other spacecraft,
04:54but I think the most important thing is that it gets in very close to the planet as part of that ellipse,
05:01brings it in a few thousand miles above those cloud tops, very close near the equator.
05:06We're going to go over the poles of Jupiter. That means we can study the magnetosphere in a different way.
05:11A magnetosphere is the sphere of influence of a magnetic field.
05:16So a planet that has a magnetic field has a magnetosphere when its sphere of influence extends beyond the planet,
05:24out into space, and affects the region around it.
05:27The magnetosphere of Jupiter is vast. So if you think of Jupiter being ten times the size of the Earth,
05:33and the magnetosphere is a hundred times the size of Jupiter.
05:40The Juno probe is the furthest NASA has sent a solar-powered spacecraft.
05:59Sunlight provides twenty-five times less energy than on Earth,
06:03which means it requires advanced solar power technology,
06:06with solar cells which are both fifty percent more efficient and more radiation-tolerant than silicon cells.
06:18The craft also houses an electronics vault, which is radiation shielded to protect the electronics aboard
06:24from the intense and deadly radiation environment around Jupiter.
06:32The probe carries a full set of sensors.
06:35A microwave radiometer for atmospheric sounding and composition study,
06:39plasma and energetic particle detectors,
06:42a vector magnetometer,
06:44a radioplasma wave experiment and ultraviolet,
06:47and an infrared imager,
06:49plus a color camera called JunoCam.
06:52In Roman mythology, which of course is rooted from Greek mythology,
07:03Juno was the wife and sister goddess of Jupiter.
07:09And Jupiter was sort of being naughty with some friends,
07:12so he cast a veil of clouds around himself and his friends.
07:15But of course Juno was a fairly powerful god herself,
07:18and used her powers to look right through the clouds
07:21and see the true nature of Jupiter and understand what he was really up to.
07:25And that's exactly what the Juno spacecraft does for us,
07:28is that it goes there with special instruments in a special orbit
07:32and uses its powers to see right through Jupiter's clouds
07:35and understand its true nature,
07:37which is holding these secrets for us about how the solar system formed
07:41and where we all came from.
07:55A long-standing feature of the storms of Jupiter is the Great Red Spot.
08:06Large enough to swallow the Earth,
08:08this storm system has been studied since the 19th century.
08:12Then it was measured at a little over 41,000 kilometers on its long axis.
08:21Voyager 1 and 2 measured it at over 23,000 kilometers,
08:25and recent observations by the Hubble Space Telescope
08:28have the red spot at only 16,500 kilometers long.
08:33It seems the rate of shrinkage is increasing.
08:35One day it will probably vanish altogether.
08:37Juno will also help confirm the theory that Jupiter was the first of the planets in the solar system
08:45to form from the primordial disk of dust and gas some 4.6 billion years ago.
08:55Juno will also help confirm the theory that Jupiter was the first of the planets in the solar system
09:01to form from the primordial disk of dust and gas some 4.6 billion years ago.
09:07I would expect Juno to tell us more about how planets work,
09:25meaning how the heat gets out, what kinds of flows exist inside the body,
09:32how magnetic fields get generated.
09:34Learning what Jupiter is made of, we will learn such a wide range of things.
09:39For indeed, Jupiter is the most massive planet in the solar system.
09:43It is the body you want to understand in order to understand the architecture of everything else, including Earth.
09:51Juno's year-long mission will end with a deorbit burn and a slow descent into the upper atmosphere,
10:17where it will continue to send back scientific data until its destruction.
10:29Perhaps the jewel of the solar system is Saturn, with her spectacular rings.
10:34All four of the outer planets have rings of ice and rock, but Saturn's is the most complicated,
10:44and with thousands of ringlets, the most visible.
10:50There are several groups of rings classified A through to G.
10:54Some are formed by shepherd moons within the rings,
10:57and by gravitational tidal effects from others outside.
11:01Yet some gaps are still unexplained.
11:16The current spacecraft at Saturn is Cassini, on its second extended mission,
11:20the Cassini Solstice mission, which is expected to be completed in 2017.
11:24It continues to watch the planet-sized storms in the atmosphere.
11:31Great white spots on Saturn are these large storms that erupt about once every year on Saturn.
11:36A year on Saturn is 29 Earth years.
11:39The great white spot that erupted in December 2010 initially presented itself as a small little white fluffy cloud that came up.
11:47And various instruments on Cassini were seeing it, and ground-based instruments seeing it as well.
11:54And as the days progressed, the storm got larger, and then it got sheared from the top and the bottom of the storm,
12:02on either side of it, and it wrapped all the way across the planet.
12:06We'd never before been able to study a storm system of this magnitude in the infrared,
12:11so we are very fortunate at this time to have a spacecraft in orbit and excellent ground-based facilities,
12:18allowing us to make a historical record of this great white spot.
12:22And that will allow us to compare it in future generations when the next one happens.
12:30Another phenomenon is a hexagon of clouds around the north pole of Saturn,
12:34which has recently come into the light.
12:36Cassini has been in orbit around Saturn for nine years,
12:42and we've been following this hexagon which surrounds the north pole.
12:47It's bigger than two Earths, and it's a wandering jet stream.
12:51But it's been winter in the north, so we have not been able to see what's at the center of the hexagon.
12:58But now it's spring, and what we've found at the center of the hexagon is a Saturn hurricane.
13:08This is a view from directly over the north pole, which is made possible by the orbit of the spacecraft,
13:14which is now taking us over the poles.
13:18The winds are flowing at 300 miles an hour, which is four times hurricane force.
13:24The fluffy white clouds in the center are about the size of Texas.
13:30We can use special filters to measure the heights of the clouds,
13:35and the red are low clouds, and the green are high clouds.
13:39We call it a Saturn hurricane because it has the eye, it has the high winds,
13:44but it's different from an Earth hurricane because it's locked to the north pole.
13:49And unlike a terrestrial hurricane, there's no ocean underneath,
13:54and that's one of the puzzles we're trying to figure out.
13:58A phenomenon first observed on Saturn by Pioneer 11 in 1979,
14:16and common to Earth as well, are polar auroras.
14:20These magnetic-generated light shows are far more spectacular on Saturn,
14:34rising hundreds of miles above the planet's poles.
14:37And unlike on Earth, where bright displays fizzle after only a few hours,
14:42auroras on Saturn can shine for days.
14:45Auroras are produced when speeding particles, accelerated by the Sun's energy,
14:58collide with gases in a planet's atmosphere.
15:01The gases fluoresce, emitting flashes of light at different wavelengths.
15:06The Hubble Space Telescope has been watching them closely.
15:18Starting in 2016, ending in 2017,
15:22these orbits will take us up and over the north and south poles of the planet.
15:26We're actually going to dive in between the innermost edge of the D-ring
15:31and the upper atmosphere of the planet itself.
15:33From that, we're going to learn how is Saturn constructed from inside out.
15:38We'll also get the magnetic field of the planet,
15:40the mass of the rings for the very first time,
15:43and get to sample a place that no spacecraft has ever flown before.
15:48This is a mission that cannot be duplicated,
15:51so we really want to take advantage of this opportunity
15:54to observe seasonal variation in the system.
15:58Uranus has had only one visitor from Earth, Voyager 2.
16:10Like the other gas giants, Uranus has a ring system,
16:13a magnetosphere, and numerous moons.
16:16There, the similarities end.
16:19Images from Voyager revealed a featureless atmosphere
16:22with no cloud patterns or storms.
16:25Uranus differs in its orientation as well.
16:28Tilted onto its side, its poles lie where other planets have their equators.
16:34Its magnetosphere is off-center and tilted as well,
16:37generating an unusual asymmetrical field.
16:40This causes Uranus's auroras to be well off the poles.
16:45Observations from Earth have shown seasonal change
16:48and increased weather activity as Uranus approached its equinox in 2007.
16:53The wind speeds on Uranus can reach 250 metres a second.
16:59Although there are currently no scheduled missions to Uranus,
17:03there have been several proposals put forward,
17:06both jointly from ESA and NASA and JPL,
17:09including both nuclear and solar power probes
17:12and an atmospheric descent probe.
17:15Ion propulsion is favoured
17:17because it allows a greater mass to be sent to the planet.
17:21Ideally, a probe could be launched in 2020
17:24with a 13-year cruise to Uranus.
17:27As this is considered a low-priority mission,
17:29no funding has yet been allocated.
17:32The eighth and last planet in our solar system is Neptune,
17:49the last of the gas giants.
17:52made of hydrogen and helium,
17:58it has trace amounts of methane,
18:00which gives the planet its beautiful blue colour.
18:03It, too, has only been visited once by Voyager.
18:13The detailed images taken at that time revealed white clouds
18:22and a massive storm marring its atmosphere with supersonic winds.
18:28The storm revolves around the planet every 18 hours.
18:33And then it rotates around its own axis
18:36like a big glob of pizza dough every 16 days.
18:44Voyager also identified a ring system
18:47and confirmed 14 moons.
18:54Triton is its largest
18:56and is believed to have been captured by the planet
18:58from the outer Kuiper belt.
19:06Voyager also discovered Neptune's magnetic field
19:20was off-centre and tilted, not unlike Uranus.
19:23Both Uranus and Neptune have had very little close-up study
19:27and various missions have been proposed
19:29to fill the gap in our understanding of these ice giants.
19:33NASA has looked into several possible missions back to Neptune,
19:50perhaps a similar probe designed to that of Cassini-Huygens,
19:53but due to fiscal and other constraints,
19:56none have been approved.
19:58The Voyager mission to the outer planets
20:07has certainly been a journey of a lifetime.
20:10Having encountered Triton as the last world we would visit,
20:14I don't see how any of the scientists could have been happier.
20:20Next stop was Pluto.
20:22When New Horizons was conceived, built and launched,
20:25Pluto was still a planet.
20:27The downgrade to dwarf made little difference to its investigation.
20:32Well, you know, the key to planetary science is
20:35that you really have to go places to get the resolution,
20:38to get up close enough to really see what's going on.
20:40We want to get up close and personal.
20:42New Horizons is the first, really, of a whole new breed of spacecraft
20:47that is focusing on a very specific task.
20:50For this mission, the questions are basic.
20:54What do Pluto and Charon look like, and what are they made of?
21:00We had to really be disciplined and say,
21:03we can't do everything.
21:04Let's focus on the primary questions
21:06and design the instruments to answer those primary questions.
21:09New Horizons was built light and launched on a very powerful rocket,
21:13breaking all previous speed records when it left Earth on a solar escape trajectory
21:19at 16.26 kilometers per second.
21:24The spacecraft passed the orbit of the Moon in just nine hours.
21:28It then cruised for just one year to reach Jupiter,
21:31where it was given a gravity boost,
21:33increasing its speed by two kilometers per second
21:36and cutting the travel time to Pluto by three years.
21:44New Horizons was the first to visit the dwarf planet
21:47and Charon, its largest moon.
21:50Pluto failed one of the three criteria to remain a fully-fledged planet.
21:55It has not cleared the neighborhood around its orbit.
21:58Pluto is part of the Kuiper belt
22:03and not the only dwarf planet residing there.
22:08This is an image of Pluto at its closest approach.
22:15It still remains a treasure trove of scientific questions
22:18and hopefully answers
22:20about the origins and evolution of the solar system.
22:28From Pluto's flyby, it is on to the unknowns of the Kuiper belt.
22:35The most numerous objects in the solar system are the ice dwarf planets
22:39that make up this donut-shaped region on the edge of the solar system.
22:51It's kind of like the asteroid belt but much bigger.
22:54It has hundreds of times more objects in it than the asteroid belt.
22:57The spacecraft will visit some of these objects in its travels.
23:01Once you have the orbit,
23:02and we know where the spacecraft is and where it's going to be,
23:06we can figure out how much fuel the spacecraft is going to need to use
23:11to get to these objects.
23:13After some careful calculations...
23:16It looked like we might actually have to burn the engines to miss the object,
23:22which was a pretty exciting concept.
23:25You know, it's a good thing we looked
23:26because you wouldn't want to run into one of these things.
23:29These coal classicals, they're pretty much as they were 4.5 billion years ago.
23:35They're little fossils.
23:37That's incredible.
23:38We have no idea what they're going to look like.
23:40New Horizons will continue to explore the outer solar system until 2026.
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