0:00:05 > 0:00:08We all love talking about the weather.
0:00:08 > 0:00:11Is it too hot or is it too cold?
0:00:11 > 0:00:13Is it too wet or too windy?
0:00:15 > 0:00:17It's a national obsession.
0:00:17 > 0:00:21But now scientists have also started looking to the heavens...
0:00:23 > 0:00:27..and wondering what the weather might be like on other planets.
0:00:29 > 0:00:33We are witnessing the birth of extra terrestrial meteorology,
0:00:33 > 0:00:36as technology is allowing astronomers to study the weather
0:00:36 > 0:00:39on other planets like never before.
0:00:41 > 0:00:45Jupiter has these very long-lived storms,
0:00:45 > 0:00:47but Saturn has these very violent storms.
0:00:49 > 0:00:53But, incredibly, today the latest telescopes are enabling astronomers
0:00:53 > 0:00:57to find and study planets beyond our solar system.
0:00:59 > 0:01:02So here we have our image of ROXs 12 b,
0:01:02 > 0:01:06which is pretty amazing to think we are imaging a planet
0:01:06 > 0:01:08400 light years away.
0:01:08 > 0:01:12And our exploration of the universe is revealing alien worlds
0:01:12 > 0:01:16with weather far stranger and more extreme than anyone
0:01:16 > 0:01:19could have ever imagined.
0:01:19 > 0:01:22A lot of the planets that we're studying so far
0:01:22 > 0:01:25are very horrible places.
0:01:25 > 0:01:27You wouldn't want to go there on vacation.
0:01:29 > 0:01:33On these planets you can get the most gigantic storm systems
0:01:33 > 0:01:34ever witnessed by mankind.
0:01:36 > 0:01:40So one side of the planet can be roasting hot while at the same time
0:01:40 > 0:01:43the other side of the planet can be freezing cold.
0:01:43 > 0:01:46On some exoplanets, the temperatures are such that the clouds
0:01:46 > 0:01:51and the rain can be made up of liquid lava droplets.
0:01:51 > 0:01:54We thought we had extreme weather on Earth,
0:01:54 > 0:01:58but it turns out that it's nothing compared to what's out there.
0:02:00 > 0:02:03So instead of having rain which is liquid water droplets like here
0:02:03 > 0:02:08on Earth, it would be raining liquid rubies.
0:02:08 > 0:02:11And the search for the weirdest weather in the universe
0:02:11 > 0:02:13is only just beginning.
0:02:26 > 0:02:30It's a delightfully warm spring morning in Greenwich, London.
0:02:31 > 0:02:35Astronomers of all ages have gathered at the Royal Observatory,
0:02:35 > 0:02:38where they're hoping to witness a rather special event.
0:02:39 > 0:02:41They're waiting to glimpse another world.
0:02:43 > 0:02:45And, unusually for astronomers,
0:02:45 > 0:02:47they've got their telescopes out during the day.
0:02:50 > 0:02:52We're here to see quite a rare astronomical event.
0:02:52 > 0:02:56I'm very excited to see it. I'm just hopeful, as we all are,
0:02:56 > 0:02:59that the clouds don't come along around midday and stay with us.
0:03:01 > 0:03:04It's a chance to get a unique perspective
0:03:04 > 0:03:06of one of our nearest neighbours.
0:03:11 > 0:03:13And to take a closer look,
0:03:13 > 0:03:17astronomer Tom Kerss has set up the Great Equatorial Telescope
0:03:17 > 0:03:20to look at the sun for the first time since 1927.
0:03:23 > 0:03:26Because at exactly 12 minutes past noon,
0:03:26 > 0:03:29the planet Mercury is due to pass in front of the sun.
0:03:42 > 0:03:45So here is Mercury emerging onto the face of the sun,
0:03:45 > 0:03:47looking very beautiful indeed.
0:03:48 > 0:03:51Over the next seven and a half hours or so,
0:03:51 > 0:03:54Mercury will gradually slink across the face of the sun
0:03:54 > 0:03:57as it overtakes us on the inside track in the solar system,
0:03:57 > 0:03:59about 52 million miles away from the Earth right now.
0:04:03 > 0:04:06Ever since we've known about the existence of other planets,
0:04:06 > 0:04:09we've wondered what these mysterious alien worlds might be like.
0:04:13 > 0:04:16Could they be potential homes for life?
0:04:16 > 0:04:18And is there any way of finding out?
0:04:22 > 0:04:25So when wondering whether other planets might be habitable or not,
0:04:25 > 0:04:29the key question we need to ask to begin with is what is the atmosphere
0:04:29 > 0:04:31actually like? What is the climate like?
0:04:31 > 0:04:33What's the weather like? Whether it would be very extreme or whether it
0:04:33 > 0:04:35would be quite pleasant and stable,
0:04:35 > 0:04:37the kind of weather we think is necessary for life.
0:04:39 > 0:04:43So what will the weather be like on Mercury?
0:04:43 > 0:04:46If we look back at the beginning of the Mercury transit we can see
0:04:46 > 0:04:49a really clean bite taken out of the sun.
0:04:49 > 0:04:53And the edge is so clean because Mercury doesn't have any appreciable
0:04:53 > 0:04:55atmosphere to speak of.
0:04:58 > 0:05:04With no real atmosphere, Mercury is effectively a dead and barren world.
0:05:06 > 0:05:08Because Mercury lacks anything that we would call an atmosphere,
0:05:08 > 0:05:11there's essentially no weather on Mercury at all.
0:05:19 > 0:05:23Mercury is unusual in our solar system because all the other planets
0:05:23 > 0:05:27do have atmospheres and so they must also have weather.
0:05:31 > 0:05:33Death Valley, California,
0:05:33 > 0:05:38one of the most extreme and alien environments on Earth.
0:05:38 > 0:05:42Planetary explorer Suzanne Smerkar has come here because it shares
0:05:42 > 0:05:47a surprising similarity to our nearest neighbour, Venus.
0:05:47 > 0:05:51Venus is the brightest object in the night sky and the reason it's so
0:05:51 > 0:05:55bright is because it's covered in thick clouds.
0:05:55 > 0:05:58And when you turn your telescope to it,
0:05:58 > 0:05:59you can see nothing of the surface,
0:05:59 > 0:06:01all you see is this bright reflection coming back at you
0:06:01 > 0:06:05because of the cloud deck that's kept it shrouded in mystery.
0:06:07 > 0:06:10We do know that Venus is similar in size to Earth,
0:06:10 > 0:06:15is a rocky world like our own, and also relatively close to us.
0:06:15 > 0:06:16So what's its climate like?
0:06:17 > 0:06:20We used to think that Venus was much like the Earth,
0:06:20 > 0:06:23maybe 50 degrees hotter because it's that much closer to the sun.
0:06:23 > 0:06:25We thought it had an atmosphere like the Earth,
0:06:25 > 0:06:28we thought it would be cool enough to have oceans.
0:06:30 > 0:06:34We even thought it was covered in steamy hot swamps,
0:06:34 > 0:06:36probably covered with verdant green life.
0:06:40 > 0:06:44But to discover what Venus was really like, we needed to go there.
0:06:49 > 0:06:53At the dawn of the space age, people started to explore.
0:06:53 > 0:06:55It was the Cold War in the '60s,
0:06:55 > 0:06:59and the Soviets and the US were sending spacecraft after spacecraft,
0:06:59 > 0:07:00trying to be the first out there.
0:07:00 > 0:07:04A huge number of spacecraft have been hurled at Venus
0:07:04 > 0:07:07and there were many attempts to get to the surface.
0:07:07 > 0:07:12In the late 1960s, the Russians succeeded.
0:07:12 > 0:07:17The one that finally made it to the surface was Venera 7 in 1967,
0:07:17 > 0:07:20and that probe fell gently through the atmosphere,
0:07:20 > 0:07:23got to the surface and survived for only about two hours.
0:07:29 > 0:07:33Before they died, the Venera probes revealed the true nature
0:07:33 > 0:07:34of Venus's climate.
0:07:38 > 0:07:41Venus has a surface temperature of 462 Celsius,
0:07:41 > 0:07:43which makes it the hottest place in the solar system.
0:07:43 > 0:07:47And the atmospheric pressure on Venus is almost 100 times
0:07:47 > 0:07:48that on the Earth.
0:07:51 > 0:07:55With surface temperatures hot enough to melt lead,
0:07:55 > 0:08:00an oppressive atmosphere of carbon dioxide, and belching clouds
0:08:00 > 0:08:05made of sulphuric acid, Venus is a planetary vision of Hell.
0:08:09 > 0:08:12We knew for the first time that Venus is not a swampy,
0:08:12 > 0:08:14verdant region teeming with life,
0:08:14 > 0:08:18but instead it's a hellish, hot inferno.
0:08:20 > 0:08:23Venus is the hottest planet in the solar system,
0:08:23 > 0:08:26but it's not the closest to the sun.
0:08:29 > 0:08:33Sue has come to Death Valley where the unbearable temperatures
0:08:33 > 0:08:36are created by the same phenomenon at work on Venus.
0:08:40 > 0:08:43We are here today in Death Valley, the hottest place on Earth.
0:08:43 > 0:08:47The temperature today is...
0:08:47 > 0:08:4842 degrees.
0:08:48 > 0:08:50Pretty balmy for Death Valley -
0:08:50 > 0:08:53the hottest recorded temperature is 57 degrees
0:08:53 > 0:08:56so we have it easy today.
0:08:56 > 0:09:01The reason that it is so hot here is that we are at 86m below sea level
0:09:01 > 0:09:05and that means that we have about 86m more atmosphere here
0:09:05 > 0:09:10and that means it's higher pressure and in fact the pressure measurement
0:09:10 > 0:09:13here is 1,016 bars.
0:09:13 > 0:09:17And that extra bit of pressure is really what's giving us
0:09:17 > 0:09:20this intense heat that we are experiencing today.
0:09:20 > 0:09:23It's like adding another layer of insulation or another blanket
0:09:23 > 0:09:26that's holding the heat in.
0:09:32 > 0:09:34And by simply driving uphill,
0:09:34 > 0:09:38Sue can reveal the tremendous insulating power of the atmosphere.
0:09:43 > 0:09:46So now we are at about 1,000m and it's already
0:09:46 > 0:09:48looking greener and a bit cooler up here.
0:09:53 > 0:09:58At Dante's View, almost 2km above the valley floor,
0:09:58 > 0:10:00the temperature is much cooler.
0:10:04 > 0:10:07We're at about 1.7km above the valley floor,
0:10:07 > 0:10:12where we were earlier today, and the temperature is 30 degrees Celsius,
0:10:12 > 0:10:15way cooler than the 42 degrees down there.
0:10:15 > 0:10:19And the reason it's so much cooler up here is that we have
0:10:19 > 0:10:22that 1.7km less air.
0:10:22 > 0:10:28Our pressure is 831 bars, down below it was 1,016.
0:10:28 > 0:10:30So the pressure is much lower.
0:10:30 > 0:10:32We have a lot less atmosphere above us,
0:10:32 > 0:10:36and as a result it's much cooler and much more pleasant up here.
0:10:40 > 0:10:44On Earth, the temperature typically increases
0:10:44 > 0:10:48by about 6.5 degrees Celsius for every kilometre you descend.
0:10:54 > 0:10:57On Venus, with its much deeper atmosphere than Earth,
0:10:57 > 0:11:00this insulating effect is taken to its extreme.
0:11:04 > 0:11:09It is so much hotter on Venus because the pressure is at 92 bars,
0:11:09 > 0:11:13almost 100 times that on the Earth, and the atmosphere is much thicker,
0:11:13 > 0:11:15much denser, and it really holds that heat in,
0:11:15 > 0:11:18making Venus the incredible inferno that it is.
0:11:20 > 0:11:24On top of this, Venus's atmosphere is almost entirely made up
0:11:24 > 0:11:26of the greenhouse gas carbon dioxide.
0:11:28 > 0:11:32And this combines with the intense pressure to make Venus
0:11:32 > 0:11:34the hottest planet in the solar system.
0:11:41 > 0:11:44Our next nearest neighbour couldn't be more different.
0:11:44 > 0:11:47Venus and Mars are like chalk and cheese.
0:11:48 > 0:11:51So Mars is the opposite extreme from Venus.
0:11:51 > 0:11:55It's atmosphere is 1/100th the pressure of Earth's
0:11:55 > 0:11:59and the effect of having that really low atmospheric pressure on Mars
0:11:59 > 0:12:03means that it can't trap any of its heat.
0:12:03 > 0:12:05So Mars is a cold,
0:12:05 > 0:12:08barren desert compared to Earth or to Venus.
0:12:09 > 0:12:11Because of its thin atmosphere,
0:12:11 > 0:12:14Mars is home to some spectacular weather phenomena.
0:12:16 > 0:12:19The rovers sent by NASA revealed that Mars is scoured
0:12:19 > 0:12:23by super-size dust devils,
0:12:23 > 0:12:25reaching up to a kilometre in height.
0:12:30 > 0:12:33But even more impressive are the dust storms,
0:12:33 > 0:12:35which dwarf those on Earth.
0:12:36 > 0:12:38In the thin atmosphere of Mars,
0:12:38 > 0:12:40the dust storms can get to a very high elevation,
0:12:40 > 0:12:43they can get to about 20km above the surface.
0:12:48 > 0:12:51And because most of Mars is a dry, dusty desert,
0:12:51 > 0:12:55these dust storms can cover vast expanses.
0:12:55 > 0:12:59In fact, it seems there is no limit to how far they can spread.
0:13:01 > 0:13:04Every few years an enormous dust storm will grow
0:13:04 > 0:13:07until the entire planet is engulfed.
0:13:07 > 0:13:11Incredibly, storms like these have been shown to envelop
0:13:11 > 0:13:14the whole of Mars for over two months.
0:13:21 > 0:13:25WEATHER REPORT: For England it's a hot and sunny day for all, any mist and fog clearing away quickly...
0:13:25 > 0:13:29Further out in the solar system, the weather gets even wilder.
0:13:31 > 0:13:34It's another fine sunny day in Pasadena,
0:13:34 > 0:13:36home of NASA's Jet Propulsion Laboratory.
0:13:38 > 0:13:42Andrew Ingersoll is the father of extra-terrestrial meteorology.
0:13:44 > 0:13:47He's come to the Deep Space Operations Centre.
0:13:47 > 0:13:51It's mission control for the small fleet of spacecraft that NASA
0:13:51 > 0:13:54has sent to explore the outer reaches of the solar system.
0:13:56 > 0:13:59Andy has worked on all these missions.
0:14:01 > 0:14:04So we've had a whole series of spacecraft
0:14:04 > 0:14:06visiting the giant planets.
0:14:06 > 0:14:11The first big one was Voyager in the '70s,
0:14:11 > 0:14:14which zoomed past all the giant planets.
0:14:14 > 0:14:16Then there was Galileo.
0:14:16 > 0:14:22Then Cassini which has been in orbit around Saturn for ten years.
0:14:23 > 0:14:28And now we have Juno in orbit around Jupiter.
0:14:28 > 0:14:31The spacecraft have given us an unprecedented view of the weather
0:14:31 > 0:14:34on these planets.
0:14:34 > 0:14:39The outer planets are big balls of gas and that makes a huge difference
0:14:39 > 0:14:41in the weather,
0:14:41 > 0:14:44so there's lots of room for weather.
0:14:44 > 0:14:46And because you don't have continents,
0:14:46 > 0:14:49you don't have mountains for the winds to rub against,
0:14:49 > 0:14:55and there's nothing to control the weather the way the continents
0:14:55 > 0:14:57partly control our weather.
0:14:57 > 0:15:01This means these planets have storms on an entirely different scale
0:15:01 > 0:15:03to ours.
0:15:03 > 0:15:09And the most famous storm of all has to be Jupiter's Great Red Spot.
0:15:09 > 0:15:13The Great Red Spot is a huge storm in Jupiter's atmosphere.
0:15:13 > 0:15:16You could put two Earths inside the Red Spot,
0:15:16 > 0:15:20and the winds going around the periphery of the Red Spot
0:15:20 > 0:15:24are about three times the speed of the Earth's jet streams.
0:15:27 > 0:15:32With winds whipping round at about 650km per hour,
0:15:32 > 0:15:36and releasing so much energy that it heats the atmosphere above it
0:15:36 > 0:15:39to around 1,400 degrees Celsius,
0:15:39 > 0:15:42the Red Spot has been raging for as long as we on Earth
0:15:42 > 0:15:45have been able to observe Jupiter.
0:15:45 > 0:15:50Shortly after Galileo built the first telescope,
0:15:50 > 0:15:53people were using these primitive telescopes to look at Jupiter
0:15:53 > 0:15:56and they saw this storm.
0:15:56 > 0:16:01And it's apparently been there ever since, which is remarkable,
0:16:01 > 0:16:04compared with Earth storms.
0:16:04 > 0:16:10The Red Spot has been there for over 350 years and that makes it
0:16:10 > 0:16:13the longest-living storm that we know of.
0:16:17 > 0:16:20Jupiter may have the longest-lasting storm,
0:16:20 > 0:16:22but it's Saturn, the next gas giant,
0:16:22 > 0:16:26that is home to the largest and most powerful storm ever seen
0:16:26 > 0:16:28in the solar system.
0:16:28 > 0:16:32And in 2010, the Cassini spacecraft was there to see it.
0:16:35 > 0:16:39Saturn, of course, is a spectacular sight because of the rings,
0:16:39 > 0:16:43and it's also rather boring as far as the weather is concerned.
0:16:43 > 0:16:45It's a bland thing.
0:16:46 > 0:16:50But every now and then - 20, 30 years -
0:16:50 > 0:16:53Saturn erupts with a giant storm,
0:16:53 > 0:16:59and Cassini was fortunate to be orbiting Saturn at the time
0:16:59 > 0:17:01of one of these eruptions.
0:17:01 > 0:17:06What happened was, on December 5th 2010,
0:17:06 > 0:17:12the radio receiver on Cassini started picking up the radio signal
0:17:12 > 0:17:13of lightning.
0:17:15 > 0:17:19And on the same day the camera saw a little storm up in
0:17:19 > 0:17:21the northern hemisphere of Saturn.
0:17:23 > 0:17:28By January it had developed into a fair-sized thing,
0:17:28 > 0:17:30and then we watched it for six months.
0:17:33 > 0:17:36During that time a huge storm grew and wrapped itself
0:17:36 > 0:17:41around the entire planet, covering 4 billion square kilometres
0:17:41 > 0:17:44until its head caught up with its tail.
0:17:47 > 0:17:52Driven by winds going at around 1,800km per hour, with huge
0:17:52 > 0:17:56lightning flashes 10,000 times stronger than those we get on Earth.
0:17:59 > 0:18:03It's very funny, Jupiter has these very long-lived storms,
0:18:03 > 0:18:07but Saturn has these very violent storms.
0:18:07 > 0:18:10We don't fully understand why there is this difference in the weather
0:18:10 > 0:18:12between Jupiter and Saturn.
0:18:12 > 0:18:14Whether it's duration or size,
0:18:14 > 0:18:17the storms on both these planets dwarf those on Earth.
0:18:21 > 0:18:24However, because they receive far less heat from the sun
0:18:24 > 0:18:29than the Earth does, something else is also powering their weather.
0:18:29 > 0:18:32The weather on Jupiter and Saturn comes from two sources.
0:18:32 > 0:18:35One is the sun, as on Earth,
0:18:35 > 0:18:38and the other is the internal heat left over
0:18:38 > 0:18:40from when the planets formed.
0:18:40 > 0:18:43It's this internal heat trying to escape through
0:18:43 > 0:18:47their deep atmospheres that makes the gas planets so tumultuous.
0:18:52 > 0:18:56This zone dry and sunny throughout the day.
0:18:56 > 0:18:59Later this afternoon there will be more in the way of clouds...
0:18:59 > 0:19:02The storms on the gas planets are certainly
0:19:02 > 0:19:05weirder and wilder than any we have on Earth,
0:19:05 > 0:19:10but when it comes to the clouds and the rain, things get even stranger.
0:19:13 > 0:19:16It's a typical June morning in Southern California...
0:19:17 > 0:19:21..and a local weather phenomenon known as the June gloom makes it
0:19:21 > 0:19:24the perfect day for taking a closer look at the clouds.
0:19:30 > 0:19:35Dr Kevin Baines has a passion for the skies, on Earth and beyond,
0:19:35 > 0:19:40and he's been studying the clouds on the gas planets.
0:19:40 > 0:19:41Coming out of SoCal,
0:19:41 > 0:19:44we're going to make a left turn on alpha
0:19:44 > 0:19:46and taxi over to the run-up area for runway one.
0:19:52 > 0:19:54So on a planet you'll get clouds at different levels,
0:19:54 > 0:19:58depending on the local temperature and the local pressure.
0:19:58 > 0:20:01On Earth, all clouds are made of water.
0:20:01 > 0:20:04So in southern California we have this marine layer.
0:20:04 > 0:20:07What happens is it actually forms over the water.
0:20:07 > 0:20:10The Pacific Ocean, of course, has a lot of water,
0:20:10 > 0:20:13so during the day it heats up and releases water into the air
0:20:13 > 0:20:16as water vapour. As this water vapour rises,
0:20:16 > 0:20:22it cools then it condenses out as water droplets in the air,
0:20:22 > 0:20:24and when you get millions and millions of water droplets,
0:20:24 > 0:20:26it forms a cloud.
0:20:26 > 0:20:30Clouds will form wherever it gets too cold for water to stay
0:20:30 > 0:20:32as a vapour in the air.
0:20:34 > 0:20:36And if there's enough moisture,
0:20:36 > 0:20:39the cloud droplets grow in size until they are big and heavy enough
0:20:39 > 0:20:40to fall as rain.
0:20:43 > 0:20:46Jupiter and Saturn also have a layer of water clouds.
0:20:51 > 0:20:54If we were to transport ourselves magically to Jupiter or Saturn,
0:20:54 > 0:20:57we could find a water layer like this.
0:20:57 > 0:21:01But other substances form clouds at colder temperatures,
0:21:01 > 0:21:03so above the layer of water clouds,
0:21:03 > 0:21:06higher up in the atmospheres of Jupiter and Saturn,
0:21:06 > 0:21:09there are two more cloud layers.
0:21:09 > 0:21:11As you climb up out of the water layer,
0:21:11 > 0:21:14it gets so cold that first you get ammonia hydrosulphide,
0:21:14 > 0:21:17which is very exotic cloud made of both ammonia
0:21:17 > 0:21:19and sulphur put together,
0:21:19 > 0:21:22and then as you climb up even higher into the atmosphere,
0:21:22 > 0:21:26when it gets down to about minus 130 Celsius,
0:21:26 > 0:21:32there ammonia gas in the atmosphere condenses out and forms clouds.
0:21:32 > 0:21:35So on these planets it doesn't just rain water,
0:21:35 > 0:21:39there could also be a light rain of liquid ammonia.
0:21:39 > 0:21:43Now if you go out to Uranus and Neptune, it is so cold out there,
0:21:43 > 0:21:45about -300 degrees,
0:21:45 > 0:21:49that you even have methane gas come out as clouds.
0:21:51 > 0:21:55And so on Uranus and Neptune, liquid methane could fall from the sky.
0:21:58 > 0:22:02Bizarre as they are, ammonia and methane aren't
0:22:02 > 0:22:04the weirdest rains of all,
0:22:04 > 0:22:08because back on Saturn, in the depths of its atmosphere,
0:22:08 > 0:22:13Kevin believes that an astonishing process is at work that creates
0:22:13 > 0:22:16what could be the strangest rain in the solar system.
0:22:21 > 0:22:25This process can be witnessed an on idyllic summer day in Oxfordshire.
0:22:28 > 0:22:31Inside this unremarkable office building,
0:22:31 > 0:22:34a manufacturing company is replicating the conditions deep
0:22:34 > 0:22:39in Saturn's atmosphere, not to study it, but for industrial purposes.
0:22:41 > 0:22:43Using these massive presses,
0:22:43 > 0:22:46they're turning carbon graphite into something far more valuable...
0:22:49 > 0:22:53..and Kevin has come over from California to see how this process
0:22:53 > 0:22:56can help explain what's happening deep inside Saturn.
0:22:58 > 0:23:01We know that on Saturn there's carbon soot.
0:23:01 > 0:23:04We know that by looking at these dark clouds that we saw with
0:23:04 > 0:23:07our camera onboard the Cassini spacecraft orbiting Saturn,
0:23:07 > 0:23:11and we see the spectroscopic signature of carbon soot there.
0:23:11 > 0:23:13The carbon soot is created by lightning,
0:23:13 > 0:23:16lightning actually zapping methane in the atmosphere.
0:23:18 > 0:23:22Something very strange then happens to the soot as it falls
0:23:22 > 0:23:24through Saturn's atmosphere.
0:23:25 > 0:23:29It is transformed into something remarkable,
0:23:29 > 0:23:33a process that is actually being replicated here.
0:23:33 > 0:23:34What we do, effectively,
0:23:34 > 0:23:39is we take this carbon graphite and mix it with several other materials
0:23:39 > 0:23:41and we assemble what we call a capsule.
0:23:41 > 0:23:45We take that capsule, the graphite material inside it,
0:23:45 > 0:23:49and we place it inside the actual press itself.
0:23:49 > 0:23:54The press is then closed up and the carbon graphite is exposed
0:23:54 > 0:23:57to extreme temperatures and pressures.
0:23:58 > 0:24:02High pressures are generated by these anvils that can press down
0:24:02 > 0:24:06onto the graphite, pressures of around 50,000 atmospheres.
0:24:06 > 0:24:10The graphite's then going to be heated to about 2,000 Celsius -
0:24:10 > 0:24:13that heating happens by large electrical currents.
0:24:14 > 0:24:18This process mimics what's happening inside Saturn.
0:24:18 > 0:24:20We know we have carbon, which is very much like the graphite
0:24:20 > 0:24:23that we just put into the machine over here.
0:24:23 > 0:24:26The carbon soot precipitates or falls through the atmosphere,
0:24:26 > 0:24:29and eventually it will get to the 7,000km level.
0:24:29 > 0:24:31At that point, it will be experiencing the pressures
0:24:31 > 0:24:35and temperatures that we experience in the press over here.
0:24:35 > 0:24:36Inside the press,
0:24:36 > 0:24:41the intense heat and crushing pressure transform the carbon
0:24:41 > 0:24:43from graphite into diamond.
0:24:48 > 0:24:49All right.
0:24:49 > 0:24:51So this may not look like diamonds,
0:24:51 > 0:24:54but we will then take this rubble and process it further
0:24:54 > 0:24:56and we'll extract the diamond.
0:24:56 > 0:24:58Great. So, the diamonds are in there somewhere?
0:24:58 > 0:25:01Somewhere inside this rubble, Kevin, there are diamonds.
0:25:05 > 0:25:06This high-temperature,
0:25:06 > 0:25:09high-pressure process can make a variety of diamonds
0:25:09 > 0:25:11which are used in industry.
0:25:23 > 0:25:25Here we have tiny triangles -
0:25:25 > 0:25:28effectively, these are used for wire drawing dies.
0:25:28 > 0:25:31You get square-shaped diamonds which, in this case,
0:25:31 > 0:25:35are used as single crystal cutting tools.
0:25:35 > 0:25:39These diamonds are yellow because they contain nitrogen.
0:25:39 > 0:25:42So what we were making earlier today, effectively,
0:25:42 > 0:25:47are these diamond grits, tiny little stones of single crystal diamonds,
0:25:47 > 0:25:49normally about 100 microns in size.
0:25:51 > 0:25:54Kevin believes the same thing is happening on Saturn.
0:25:56 > 0:25:58So we really think it's very similar conditions,
0:25:58 > 0:26:00very similar process that's happening.
0:26:00 > 0:26:02At the 7,000km level in Saturn,
0:26:02 > 0:26:05carbon soot will transform itself into diamonds,
0:26:05 > 0:26:06creating a diamond rain.
0:26:09 > 0:26:12As the carbon soot falls from the clouds,
0:26:12 > 0:26:15the extreme temperature and pressure deep in the atmosphere
0:26:15 > 0:26:17turn it into diamonds.
0:26:20 > 0:26:23So inside Saturn we have a huge region of diamond rain.
0:26:28 > 0:26:32Our exploration of the other planets in our solar system has revealed
0:26:32 > 0:26:36weather stranger and more powerful than anything we have here on Earth.
0:26:39 > 0:26:42But what about beyond our solar system?
0:26:42 > 0:26:46What is the weather like in the rest of the universe?
0:26:50 > 0:26:52Some of those showers could be quite heavy. They'll be some dry spells
0:26:52 > 0:26:56in between, but limited brightness and it will be a cool one...
0:26:56 > 0:26:59Perched at the top of Mauna Kea in Hawaii,
0:26:59 > 0:27:034,000m above sea level, is the Keck Observatory,
0:27:03 > 0:27:07one of the pre-eminent earthbound telescopes for finding planets
0:27:07 > 0:27:10orbiting other stars, known as exoplanets.
0:27:14 > 0:27:18Brendan Bowler has one of the best jobs in the world -
0:27:18 > 0:27:21he's an exoplanet explorer.
0:27:21 > 0:27:24I feel incredibly lucky studying astronomy and contributing
0:27:24 > 0:27:27to exoplanetary science.
0:27:27 > 0:27:28It's humbling, in many ways,
0:27:28 > 0:27:34to be able to contribute and answer some of the questions
0:27:34 > 0:27:38that we've been thinking about as humans for millennia.
0:27:38 > 0:27:43The aim of my job is to find planets orbiting other stars,
0:27:43 > 0:27:45which is a very difficult task to do.
0:27:47 > 0:27:49Planets are both much smaller,
0:27:49 > 0:27:54much lower mass and much fainter than the stars that they orbit,
0:27:54 > 0:27:58so trying to find planets in the glare of their stars
0:27:58 > 0:28:00is very difficult.
0:28:00 > 0:28:05So it's as if we're trying to find a firefly buzzing around a spotlight
0:28:05 > 0:28:08that's 10 billion times brighter than that firefly,
0:28:08 > 0:28:11from a distance of New York all the way to London.
0:28:15 > 0:28:19So how do you find a planet orbiting a distant star,
0:28:19 > 0:28:21let alone study its weather?
0:28:23 > 0:28:28There are two indirect methods that we primarily use to find planets.
0:28:28 > 0:28:31The first is the radial velocity technique.
0:28:31 > 0:28:35Let's say this is the planet and the post is the star that it's orbiting.
0:28:35 > 0:28:38As a planet orbits its star,
0:28:38 > 0:28:42the planet exerts gravitational influence on the host star,
0:28:42 > 0:28:44which causes the host star to wobble.
0:28:47 > 0:28:50We can search for planets by looking for the back and forth wobble
0:28:50 > 0:28:52that planets induce on their host stars.
0:28:54 > 0:28:58And that's exactly how the first exoplanet orbiting a sun-like star
0:28:58 > 0:29:04was discovered, in 1995, changing the face of astronomy for ever.
0:29:04 > 0:29:09And since then, planet hunters have discovered thousands more
0:29:09 > 0:29:10orbiting distant stars.
0:29:14 > 0:29:17But planetary explorers aren't satisfied
0:29:17 > 0:29:20with simply finding planets.
0:29:20 > 0:29:23What we really want to do is to be able to characterise the planet
0:29:23 > 0:29:25in more detail.
0:29:25 > 0:29:28The radial velocity method only tells us about
0:29:28 > 0:29:30the mass of the planet.
0:29:30 > 0:29:33The bigger the wobble, the bigger the mass,
0:29:33 > 0:29:37but luckily there's a second technique for finding planets
0:29:37 > 0:29:42known as the transit method, which reveals a whole lot more.
0:29:42 > 0:29:46The transit method you can think of as a planet crossing between us,
0:29:46 > 0:29:51our line of sight, and the star that it orbits, just like this.
0:29:51 > 0:29:53Now when that crossing event occurs,
0:29:53 > 0:29:57it will cause a dip in the brightness of that host star.
0:29:57 > 0:30:00So we can use that to find planets,
0:30:00 > 0:30:04by searching for periodic dips in the brightness of that star.
0:30:07 > 0:30:12Crucially, the transit method also tells us how big the planet is,
0:30:12 > 0:30:14because the bigger the planet,
0:30:14 > 0:30:17the greater the dip in the light from the star.
0:30:18 > 0:30:21The transit method tells us about the size of the planet,
0:30:21 > 0:30:25while the radial velocity tells us about the mass of the planet,
0:30:25 > 0:30:31so we can use both of those together to measure the density of planets,
0:30:31 > 0:30:34because density is mass over volume.
0:30:34 > 0:30:37And this reveals what the planet is made of.
0:30:37 > 0:30:40Small dense planets are rocky,
0:30:40 > 0:30:45whereas large planets that are not dense are gas giants.
0:30:47 > 0:30:52The first planets discovered were huge gas giants like Jupiter,
0:30:52 > 0:30:56and since then, planet hunters have found all sorts of combinations
0:30:56 > 0:31:01of size and mass, including small, dense planets,
0:31:01 > 0:31:03rocky worlds that could have atmospheres.
0:31:06 > 0:31:10But finding out any more detail about an exoplanet's atmosphere,
0:31:10 > 0:31:15climate and, ultimately, its weather, is extremely difficult.
0:31:18 > 0:31:20But not impossible.
0:31:21 > 0:31:25The key to doing this is the fact that different gases absorb light
0:31:25 > 0:31:27at different wavelengths.
0:31:30 > 0:31:34So we can study the composition of the atmospheres of exoplanets
0:31:34 > 0:31:37by breaking up the light that we receive at Earth
0:31:37 > 0:31:39into its constituent colours.
0:31:39 > 0:31:41This is what we're doing here with the projector which emits
0:31:41 > 0:31:44white light - we're dispersing it with a prism,
0:31:44 > 0:31:48spreading out the light. We can see the various wavelengths and colours
0:31:48 > 0:31:50it's split into.
0:31:50 > 0:31:53If we have a gas intervening between the projector
0:31:53 > 0:31:57and the prism, then the different colours will be blocked out,
0:31:57 > 0:31:59depending on the nature of the gas.
0:31:59 > 0:32:03So what I'm going to do is put a gas in this beam of light
0:32:03 > 0:32:06by burning baking soda, which is sodium bicarbonate.
0:32:08 > 0:32:09So here we have our baking soda.
0:32:11 > 0:32:14We'll drop a little bit of that into the flame.
0:32:16 > 0:32:20And so what we're doing is making the equivalent of an atmosphere
0:32:20 > 0:32:25of sodium atoms in the beam, which is absorbing some of the light.
0:32:25 > 0:32:28What we see on the spectrum is a narrow dark line that comes and goes
0:32:28 > 0:32:31as I drop it in, in the yellow part of the spectrum,
0:32:31 > 0:32:35which corresponds to the wavelength that sodium absorbs.
0:32:35 > 0:32:39Every chemical has its own unique pattern of absorption lines.
0:32:42 > 0:32:45So astronomers can use this information to detect
0:32:45 > 0:32:49the different substances in the atmospheres of planets.
0:32:49 > 0:32:54And that's exactly what Brendan is going to try to do tonight.
0:32:54 > 0:32:58He's pointing the Keck telescope's awesome light gathering power
0:32:58 > 0:32:59at a newly discovered planet.
0:33:02 > 0:33:06I'll be using the Keck telescope to study a planet
0:33:06 > 0:33:08about 400 light years away.
0:33:08 > 0:33:11Its name is ROXs 12 b,
0:33:11 > 0:33:15it has a mass between 10-15 times that of Jupiter,
0:33:15 > 0:33:17and we know it's a gas giant, but we don't know what it's made out of,
0:33:17 > 0:33:20which is the goal of our observations.
0:33:20 > 0:33:23By studying the light that is emitted from this planet,
0:33:23 > 0:33:26we'll be able to learn about the chemical composition and physical
0:33:26 > 0:33:28properties of its atmosphere.
0:33:33 > 0:33:35ROXs 12 is about to rise.
0:33:35 > 0:33:37We have two more minutes.
0:33:37 > 0:33:40It's below the telescope limits, but it is about to go up,
0:33:40 > 0:33:43and then we can slew to it.
0:33:43 > 0:33:45We're trying to look in the infrared,
0:33:45 > 0:33:49to both image the planet and get a spectrum of it.
0:33:49 > 0:33:52When we can get a spectrum of the planet,
0:33:52 > 0:33:54we can learn what's in its atmosphere.
0:33:56 > 0:33:59Direct imaging of distant planets like this
0:33:59 > 0:34:03is at the very cutting edge of astronomy.
0:34:03 > 0:34:06It's incredibly difficult to image planets,
0:34:06 > 0:34:09but for the most massive planets, like ROXs 12 b,
0:34:09 > 0:34:13it emits enough light that we can actually detect the photons,
0:34:13 > 0:34:17so we can see the planet and take pictures of the planet.
0:34:17 > 0:34:20And for this, we need our very best telescopes.
0:34:21 > 0:34:25Keck is the biggest telescope in the world,
0:34:25 > 0:34:28so we need the size of the mirror, which is ten metres in diameter,
0:34:28 > 0:34:30to gather enough photons.
0:34:31 > 0:34:36Incredibly, the Keck telescope also compensates for interference
0:34:36 > 0:34:38from our own atmosphere.
0:34:40 > 0:34:44Stars twinkle because of turbulence in the Earth's atmosphere.
0:34:44 > 0:34:47We don't like that twinkling, we want it to stop,
0:34:47 > 0:34:51so we use adaptive optics to actively compensate, in real time,
0:34:51 > 0:34:55thousands of times per second, for that turbulence.
0:34:55 > 0:34:57It's as if we're putting these big telescopes that we have
0:34:57 > 0:34:59on the ground in space.
0:35:02 > 0:35:05So far, only a handful of planets have ever been
0:35:05 > 0:35:07directly imaged like this.
0:35:07 > 0:35:09Martha, what are the coordinates?
0:35:09 > 0:35:1216, 26, 28.1.
0:35:14 > 0:35:18Can you go to ROXs 12 and the moon and look how it looks in the tracks?
0:35:18 > 0:35:19Yeah.
0:35:19 > 0:35:22That's it finished, and we're ready.
0:35:22 > 0:35:25This is our sixth attempt to get this target.
0:35:25 > 0:35:29We've been weathered out, we've had instrument issues,
0:35:29 > 0:35:32and we think we're finally going to get it tonight.
0:35:34 > 0:35:37OK, so I think we have the target centred up
0:35:37 > 0:35:40in the field of view here.
0:35:40 > 0:35:42I think we can start...
0:35:42 > 0:35:43exposing.
0:35:53 > 0:35:56So, here we have our image of ROXs 12 b.
0:35:56 > 0:36:00So this is an infrared image of this planet,
0:36:00 > 0:36:04which is pretty amazing to think that we are imaging a planet
0:36:04 > 0:36:05400 light years away.
0:36:07 > 0:36:11ROXs 12 b is one of only 15 exoplanets
0:36:11 > 0:36:14to have ever been directly imaged.
0:36:16 > 0:36:20And, incredibly, the faint light captured in this picture
0:36:20 > 0:36:24will reveal the secrets of ROXs 12 b's atmosphere,
0:36:24 > 0:36:28the first step towards understanding its weather.
0:36:28 > 0:36:30We're looking at the infrared light from this planet.
0:36:30 > 0:36:33This is light that's emitted in the interior of the planet
0:36:33 > 0:36:38and passed through its atmosphere, and whatever chemicals, molecules,
0:36:38 > 0:36:39atoms are in the atmosphere,
0:36:39 > 0:36:43will induce absorption features in the spectrum,
0:36:43 > 0:36:45and that's what we're looking for.
0:36:45 > 0:36:48So here we can actually get a spectrum in real-time,
0:36:48 > 0:36:49and let's go ahead and do it.
0:36:51 > 0:36:56So here's our spectrum of ROXs 12 b in the infrared.
0:36:56 > 0:36:59What we're looking for are absorption features
0:36:59 > 0:37:00from carbon monoxide, CO.
0:37:03 > 0:37:06So we can see these two dips here in the spectrum,
0:37:06 > 0:37:09which correspond to the wavelengths where CO absorbs,
0:37:09 > 0:37:12and that means that this planet really does have carbon monoxide
0:37:12 > 0:37:13in its atmosphere.
0:37:15 > 0:37:18The spectrum also revealed that this exoplanet has water vapour,
0:37:18 > 0:37:23iron hydride, vanadium oxide, potassium and sodium
0:37:23 > 0:37:26in its atmosphere - fairly typical for an exoplanet.
0:37:27 > 0:37:30So by studying the light from exoplanets
0:37:30 > 0:37:32hundreds of light years away,
0:37:32 > 0:37:35astronomers are able to detect what's in their atmosphere...
0:37:39 > 0:37:42..a key ingredient that goes into creating their weather.
0:37:50 > 0:37:52Later today, a mixture of brighter spells
0:37:52 > 0:37:55and showers for the majority...
0:37:55 > 0:37:59As well as being able to detect the gases in a planet's atmosphere,
0:37:59 > 0:38:02scientists can also use the infrared light to work out
0:38:02 > 0:38:04just how hot a planet is.
0:38:08 > 0:38:11It's a blustery day in California
0:38:11 > 0:38:14and exoplanet meteorologist Heather Knutson
0:38:14 > 0:38:16is visiting Santa Monica Pier.
0:38:18 > 0:38:21So the main thing that determines the temperature of a planet
0:38:21 > 0:38:24is the distance that it is from its host star.
0:38:24 > 0:38:26Planets that are really close in are going to be boiling hot.
0:38:26 > 0:38:29Planets that are further away will be a little bit cooler
0:38:29 > 0:38:31by comparison.
0:38:31 > 0:38:35Most of the exoplanets discovered so far are close to their stars,
0:38:35 > 0:38:39so scientists expected them to be hot,
0:38:39 > 0:38:41but they didn't know how hot.
0:38:41 > 0:38:43So we can actually go and measure the temperature of these planets
0:38:43 > 0:38:46by measuring their brightness in infrared light.
0:38:46 > 0:38:49Hotter things are going to glow more brightly in infrared wavelengths,
0:38:49 > 0:38:53cooler things are going to be a little bit dimmer and fainter.
0:38:55 > 0:38:58So probably the hottest planet that we know of is a planet
0:38:58 > 0:38:59called WASP-33 b.
0:39:01 > 0:39:05WASP-33 b is the hottest planet discovered so far
0:39:05 > 0:39:08in the entire universe.
0:39:08 > 0:39:12It's a gas giant, four and a half times the size of Jupiter.
0:39:12 > 0:39:17Its atmosphere is a scorching 3,200 Celsius.
0:39:19 > 0:39:21So this planet is hot for two reasons -
0:39:21 > 0:39:23one is it's very close to its host star.
0:39:23 > 0:39:28The other is it orbits a star that is bigger and hotter than the sun.
0:39:28 > 0:39:30Both those things together combine to make this
0:39:30 > 0:39:33one of the hottest planets we've discovered.
0:39:35 > 0:39:40Planets like WASP-33 b are nicknamed Hot Jupiters,
0:39:40 > 0:39:42and they don't just have extreme temperatures...
0:39:44 > 0:39:47..because being close to their star has another important effect
0:39:47 > 0:39:50on the weather.
0:39:50 > 0:39:54So all planets spin on their axis, just like I am now.
0:39:54 > 0:39:56The Earth spins once every 24 hours,
0:39:56 > 0:39:59but not all planets spin at the same speed.
0:39:59 > 0:40:02There are some planets which we're discovering which are very,
0:40:02 > 0:40:04very close to their stars.
0:40:04 > 0:40:08They're so close that the star tugs on the planet as it spins around
0:40:08 > 0:40:12on its axis, and the tugging of that star actually slows
0:40:12 > 0:40:15the planet's rotation down,
0:40:15 > 0:40:18keeps slowing it down and keeps slowing it down until the planet
0:40:18 > 0:40:23rotates at exactly the same speed that it orbits.
0:40:23 > 0:40:26So the same side of the planet always faces towards the star,
0:40:26 > 0:40:28just like I'm always facing the centre of this ride here.
0:40:30 > 0:40:32We call this tidal locking,
0:40:32 > 0:40:35and it means the planet has a permanent day side
0:40:35 > 0:40:37and a permanent night side.
0:40:38 > 0:40:41And being tidally locked has a dramatic impact.
0:40:43 > 0:40:46So whenever you have one part of a planet that's hot and another part
0:40:46 > 0:40:50that's cold, the natural result is that you get a wind moving
0:40:50 > 0:40:51from one part to another.
0:40:52 > 0:40:56Here at the beach during the day the land heats up but the sea stays
0:40:56 > 0:40:59relatively cold, and so you get this nice wind moving from the ocean
0:40:59 > 0:41:02towards the land that's trying to even out the temperatures.
0:41:02 > 0:41:05So when we first discovered these very close-in planets,
0:41:05 > 0:41:09we realised they were probably close enough to be tidally locked.
0:41:09 > 0:41:11And one of the very first things we wanted to know is what that meant
0:41:11 > 0:41:13for the planet's atmosphere.
0:41:13 > 0:41:16Did it mean these planets had a boiling hot day side
0:41:16 > 0:41:18and a freezing cold night side?
0:41:18 > 0:41:20Or were there winds in the atmosphere that were able to carry
0:41:20 > 0:41:23some of that heat around to the night side?
0:41:25 > 0:41:29To find out, Heather mapped the temperature on a Hot Jupiter...
0:41:32 > 0:41:35..which scientists think is blue in colour.
0:41:35 > 0:41:39The particular planet we decided to look at was a Hot Jupiter
0:41:39 > 0:41:41called HD 189733.
0:41:41 > 0:41:44That's kind of a mouthful, but I can tell you that this is actually
0:41:44 > 0:41:47my favourite Hot Jupiter, this was one of the very first planets
0:41:47 > 0:41:49that I looked at when I was a grad student.
0:41:49 > 0:41:51By looking at it in infrared,
0:41:51 > 0:41:53Heather was able to measure its temperature.
0:41:55 > 0:41:56So this is the map we made.
0:41:56 > 0:41:59So the colour tells you the temperature of different parts
0:41:59 > 0:42:03of the atmosphere. So here on the day side things are relatively hot,
0:42:03 > 0:42:07so the day side is about 900 degrees Centigrade.
0:42:07 > 0:42:10Here, on the edges, that's the night side,
0:42:10 > 0:42:12and that's a relatively cool part of the atmosphere,
0:42:12 > 0:42:16it's only 700 degrees Centigrade, which is still really hot.
0:42:16 > 0:42:19That difference is actually much smaller than we expected,
0:42:19 > 0:42:22and the fact it's so small suggested to us that this planet must have
0:42:22 > 0:42:26strong winds circulating through its atmosphere and carrying that hot air
0:42:26 > 0:42:29from the day side around to the night side.
0:42:31 > 0:42:36Incredibly, these winds have now been measured directly,
0:42:36 > 0:42:41and it turns out that HD 189733 b is home
0:42:41 > 0:42:44to the fastest winds in the universe
0:42:44 > 0:42:50which rage around it at about 8,700km per hour,
0:42:50 > 0:42:52seven times the speed of sound,
0:42:52 > 0:42:57and 20 times faster than the fastest winds ever experienced on Earth.
0:42:59 > 0:43:02Showers, some of them of sleet and snow.
0:43:02 > 0:43:08Elsewhere fewer showers and here the showers will be of rain...
0:43:08 > 0:43:11It's a beautiful tropical morning on the Big Island in Hawaii.
0:43:14 > 0:43:18Exoplanet expert Hannah Wakeford is taking to the skies
0:43:18 > 0:43:22to explore another bizarre effect the extreme heat on exoplanets
0:43:22 > 0:43:23has on their weather.
0:43:27 > 0:43:30The strangest thing about exoplanets is the clouds and the rain -
0:43:30 > 0:43:33they're nothing like we have here on Earth.
0:43:33 > 0:43:37Spectroscopy has revealed that exoplanets have clouds,
0:43:37 > 0:43:40and also what these clouds might be made of.
0:43:40 > 0:43:42We know that exoplanets have clouds.
0:43:42 > 0:43:44If we have a planet that we know should be gaseous because of
0:43:44 > 0:43:48its density but we don't detect any spectral signatures from that gas,
0:43:48 > 0:43:51then we think there must be clouds in the way which are blocking that
0:43:51 > 0:43:54light and obscuring our view.
0:43:54 > 0:43:56And sometimes we can detect signatures directly from
0:43:56 > 0:43:59those clouds by the way that they scatter or reflect the light.
0:44:03 > 0:44:06But these aren't clouds we'd recognise.
0:44:09 > 0:44:12A lot of the exoplanets that we've been able to follow up are very hot,
0:44:12 > 0:44:14over 1,000 degrees,
0:44:14 > 0:44:17so we know that water can't exist as a liquid at those temperatures,
0:44:17 > 0:44:20so they're not going to be clouds like we have here on Earth.
0:44:22 > 0:44:24Woo, we're in a cloud!
0:44:26 > 0:44:27So, on some exoplanets,
0:44:27 > 0:44:31the clouds will be made of far more exotic substances.
0:44:33 > 0:44:36The temperatures are such that substances that we think of
0:44:36 > 0:44:39as solids on Earth can actually exist as liquids or gas
0:44:39 > 0:44:41in exoplanet atmospheres.
0:44:43 > 0:44:46We can get a glimpse of this on Earth in volcanoes,
0:44:46 > 0:44:50where temperatures can reach over 1,000 degrees Celsius.
0:44:52 > 0:44:55Down there is the crater of Pu'u 'O'o,
0:44:55 > 0:44:59and you can see the lava bubbling away.
0:44:59 > 0:45:02The temperature of this lava lake is around 1,000 degrees
0:45:02 > 0:45:04and all of the rock has melted.
0:45:04 > 0:45:07The metals and minerals and the silicates that make up
0:45:07 > 0:45:12the Earth's crust have all become molten.
0:45:12 > 0:45:16It's amazing - you can really feel the temperature from the lava lake
0:45:16 > 0:45:19all the way up here. It's really very hot.
0:45:21 > 0:45:24It's 1,000 degrees melting the Earth's crust down there,
0:45:24 > 0:45:26so it's no surprise.
0:45:28 > 0:45:32And it's these substances that are thought to make up the clouds
0:45:32 > 0:45:34on some exoplanets.
0:45:35 > 0:45:38There's a planet called 55 Cancri e
0:45:38 > 0:45:40that we think is rocky because of its density,
0:45:40 > 0:45:44but it orbits very close to its parent star and is tidally locked,
0:45:44 > 0:45:48so temperatures on the day side should be high enough to melt the rock,
0:45:48 > 0:45:50making it a lava planet.
0:45:54 > 0:45:5755 Cancri e is a lava planet.
0:45:57 > 0:46:01While its night side will be relatively cool and solid rock,
0:46:01 > 0:46:06its day side is an ocean of permanently molten lava.
0:46:06 > 0:46:11On the day side, the temperatures go over 2,500 degrees.
0:46:11 > 0:46:15This is hot enough to vaporise the rock at the surface.
0:46:15 > 0:46:19This can then be lifted into the atmosphere and condensed
0:46:19 > 0:46:22to form clouds of liquid lava droplets that then can be
0:46:22 > 0:46:25transported to colder parts of the planet,
0:46:25 > 0:46:28where they will rain down as pebbles on the surface.
0:46:34 > 0:46:37So on some planets, it rains rock
0:46:37 > 0:46:39rather than water like it does here in Hawaii.
0:46:50 > 0:46:52Back on the ground on Kilauea,
0:46:52 > 0:46:55Hannah has an example of what rock rain might be like.
0:47:00 > 0:47:03Right here was the site of a massive eruption.
0:47:03 > 0:47:05All along this fissure,
0:47:05 > 0:47:10fountains of lava shot into the air nearly 100m high.
0:47:10 > 0:47:14The liquid lava droplets then cooled and solidified in the air
0:47:14 > 0:47:19before raining down onto the surface as these tiny pebbles,
0:47:19 > 0:47:23and sometimes we get these perfect little droplets called Pele's tears.
0:47:25 > 0:47:29This is what we think the rain might be like an planets like 55 Cancri e.
0:47:40 > 0:47:45But perhaps the strangest rain in the entire universe has been discovered
0:47:45 > 0:47:50on a giant gas planet which orbits a star hundreds of light years away.
0:47:53 > 0:47:57We've been able to study the exoplanet WASP-12b
0:47:57 > 0:48:00and the way that it scatters light suggests that there are clouds
0:48:00 > 0:48:02high up in the atmosphere.
0:48:02 > 0:48:06At this part of the atmosphere, the temperature is around 2,000 degrees,
0:48:06 > 0:48:09so the most likely substance forming these clouds
0:48:09 > 0:48:11is an aluminium oxide called corundum,
0:48:11 > 0:48:14which forms the basis of rubies.
0:48:14 > 0:48:18So instead of having rain which is liquid water droplets
0:48:18 > 0:48:21like here on Earth, it would be raining rubies.
0:48:28 > 0:48:32We are only just witnessing the birth of exoplanet meteorology.
0:48:32 > 0:48:37But so far, what astronomers have discovered on exoplanets
0:48:37 > 0:48:42is even more extreme and bizarre than anything anyone had imagined.
0:48:49 > 0:48:51Compared to what's out there,
0:48:51 > 0:48:55the most extreme weather on Earth - our hurricanes and tornadoes,
0:48:55 > 0:48:59our rain and our snow - all seem pretty mild.
0:48:59 > 0:49:02Our climate and weather is actually very hospitable.
0:49:02 > 0:49:07The Earth is a nice place and that's all because of the weather.
0:49:07 > 0:49:10We've got warm temperatures - not too hot, not too cold.
0:49:10 > 0:49:11It's a great place.
0:49:13 > 0:49:17Ultimately, the planet hunters of the world are hoping to find one thing -
0:49:17 > 0:49:19another Earth.
0:49:20 > 0:49:24A small, rocky planet with a thin blue line encircling it.
0:49:24 > 0:49:27A planet with a nice climate,
0:49:27 > 0:49:29a climate that could be hospitable to life.
0:49:31 > 0:49:35What we're really looking for is rocky terrestrial-type planets
0:49:35 > 0:49:38with an atmosphere around them which is habitable.
0:49:40 > 0:49:43We'd like that planet to be at the right temperature to have liquid water,
0:49:43 > 0:49:47so that means being at just the right distance from your stars
0:49:47 > 0:49:51and having exactly the right kind of atmosphere.
0:49:51 > 0:49:54But so far, astronomers have mainly found planets
0:49:54 > 0:49:56with extreme environments -
0:49:56 > 0:50:00planets with ruby rain or lava clouds.
0:50:00 > 0:50:04So the planets that we've found so far aren't particularly nice places to go.
0:50:04 > 0:50:08They're not somewhere you would put on your vacation list any time soon.
0:50:08 > 0:50:11Because at the moment, it's easier to both find and study
0:50:11 > 0:50:13the bigger planets...
0:50:13 > 0:50:14When you're looking at other stars,
0:50:14 > 0:50:19it's easy to find the large planets like Jupiter and Saturn,
0:50:19 > 0:50:22where you don't have the right kind of atmosphere.
0:50:22 > 0:50:24..or ones that are close to their stars.
0:50:24 > 0:50:27Our surveys are really good at finding planets that are very close
0:50:27 > 0:50:30to their stars, which means mostly the planets that we've discovered
0:50:30 > 0:50:34are much too hot to host life as we know it on Earth.
0:50:34 > 0:50:39Just over 20 years ago, astronomers began finding exoplanets.
0:50:39 > 0:50:43The first were giant Hot Jupiters orbiting close to their stars,
0:50:43 > 0:50:46because they were the easiest to spot.
0:50:46 > 0:50:50And now hundreds of smaller rocky planets have also been found,
0:50:50 > 0:50:53but most of these are still larger than Earth
0:50:53 > 0:50:55and still too close to their stars.
0:50:58 > 0:51:02But the search for another Earth is still in its infancy.
0:51:05 > 0:51:09Dr Brice Demory is a planet hunter
0:51:09 > 0:51:13and he may have found the promised land of planetary exploration -
0:51:13 > 0:51:16a planet that could have warm, mild weather,
0:51:16 > 0:51:19weather just like a lovely summer evening in Cambridge.
0:51:21 > 0:51:23So we are looking for rocky planets
0:51:23 > 0:51:28similar to the Earth in size and located at the right distance from its star.
0:51:28 > 0:51:30It is a bit like cooking a marshmallow -
0:51:30 > 0:51:33If the marshmallow is too close to the fire, then it will burn,
0:51:33 > 0:51:35if it is too far away, it will never cook.
0:51:35 > 0:51:39So we want the planet to be at the distance that is just right
0:51:39 > 0:51:41for habitable conditions to happen.
0:51:42 > 0:51:46We have just found three Earth-sized planets that are orbiting
0:51:46 > 0:51:49a very cool star called Trappist-1,
0:51:49 > 0:51:51and these planets are remarkable.
0:51:51 > 0:51:55The first one is located here and receives about four times the level
0:51:55 > 0:51:58of radiation that the Earth does.
0:51:58 > 0:52:00The second one, look at it here,
0:52:00 > 0:52:04receives twice the level of radiation that the Earth does.
0:52:04 > 0:52:08Those planets are probably too hot to be habitable.
0:52:08 > 0:52:10The third one is the most interesting one.
0:52:10 > 0:52:13We're not exactly sure of its location right now,
0:52:13 > 0:52:16but we believe it is located just here,
0:52:16 > 0:52:19where it would receive about the same level of radiation
0:52:19 > 0:52:22as the Earth does.
0:52:22 > 0:52:25So this is our best candidate to date for habitability prospects.
0:52:27 > 0:52:31Could this planet really be another Earth?
0:52:31 > 0:52:33As ever, this will depend on its atmosphere.
0:52:35 > 0:52:39The atmosphere dramatically affects the habitability of a planet.
0:52:39 > 0:52:41In the solar system, Venus,
0:52:41 > 0:52:45the Earth and Mars are all within a very close habitable zone,
0:52:45 > 0:52:49but the atmosphere of Venus and Mars make them completely un-habitable.
0:52:52 > 0:52:55Even if this planet has the right type of atmosphere,
0:52:55 > 0:52:59it could still be very different to Earth.
0:52:59 > 0:53:01These three planets are tidally locked to their star,
0:53:01 > 0:53:04meaning that they show permanent day side that would too hot for
0:53:04 > 0:53:08habitability and a permanent night side that would be too cold,
0:53:08 > 0:53:12while still having hospitable temperatures between the two.
0:53:12 > 0:53:13It is a bit like this marshmallow -
0:53:13 > 0:53:16if I put it in the fire and I don't rotate it,
0:53:16 > 0:53:21one side will be completely burnt while the other will be uncooked.
0:53:21 > 0:53:23But in the middle, it would be just right.
0:53:24 > 0:53:28These planets could have a barren, frozen wasteland on the night side,
0:53:28 > 0:53:33a baking inferno on their day side and yet have a temperate
0:53:33 > 0:53:36and yet have a potentially habitable strip down the middle
0:53:36 > 0:53:38where it is permanent twilight.
0:53:43 > 0:53:46But if you have a thick atmosphere surrounding this planet
0:53:46 > 0:53:49then all the heat coming from the star on the day side
0:53:49 > 0:53:51will recirculate to the night side,
0:53:51 > 0:53:54making the day side cooler and the night side warmer.
0:53:57 > 0:54:00To really know if any of these planets could be habitable,
0:54:00 > 0:54:03we need to study their atmospheres.
0:54:04 > 0:54:08But they are too small for even our best telescopes.
0:54:12 > 0:54:16So the atmospheres in small planets actually are very thin.
0:54:16 > 0:54:18So it is very difficult to detect them,
0:54:18 > 0:54:21even with the state-of-the-art telescopes that we have today.
0:54:23 > 0:54:27We have reached the limits of our current technology,
0:54:27 > 0:54:32but NASA is building a new space telescope called the James Webb,
0:54:32 > 0:54:36which will enable us to study the atmospheres of exoplanets
0:54:36 > 0:54:39in far more detail than is possible today.
0:54:39 > 0:54:42It will have far greater light-gathering abilities
0:54:42 > 0:54:45than its predecessor, the Hubble Space Telescope.
0:54:45 > 0:54:50James Webb will have a mirror diameter of 6.5m,
0:54:50 > 0:54:55which compared to the 2.4m of Hubble means that James Webb
0:54:55 > 0:54:59will collect seven times more photons than Hubble does,
0:54:59 > 0:55:02which means it will have more signal to study these planets.
0:55:03 > 0:55:07The James Webb will also be able to look at a far greater range
0:55:07 > 0:55:08of wavelengths.
0:55:08 > 0:55:11So the James Webb will have the possibility to go
0:55:11 > 0:55:16much further in infrared than what Hubble is able to do today,
0:55:16 > 0:55:20which means that it will give us the ability to probe for many more
0:55:20 > 0:55:23chemical compounds than what we are able to do with Hubble.
0:55:24 > 0:55:28When James Webb launches in 2018,
0:55:28 > 0:55:32astronomers are going to be able to study Earth-sized planets
0:55:32 > 0:55:35and discover if they are potentially habitable.
0:55:37 > 0:55:41I'm convinced that we will find a habitable planet maybe in the next
0:55:41 > 0:55:42five or ten years.
0:55:42 > 0:55:45There are so many planets in our galaxy,
0:55:45 > 0:55:48and this is the result of the last 20 years of planet hunting,
0:55:48 > 0:55:51that based on sheer probability we will definitely find
0:55:51 > 0:55:54at least another habitable planet.
0:55:57 > 0:56:01But, for the time being, our planet remains unique.
0:56:01 > 0:56:06Our exploration of other worlds so far suggests that it is a fairly rare
0:56:06 > 0:56:10combination of factors that make our climate and weather so hospitable.
0:56:11 > 0:56:16What makes the Earth so perfect for life is that first off it is rocky.
0:56:16 > 0:56:18It has also got an atmosphere around it.
0:56:18 > 0:56:21And our atmosphere is just right.
0:56:21 > 0:56:23The size and the mass of our atmosphere is critical.
0:56:28 > 0:56:31And, in addition, the composition of the atmosphere is just right.
0:56:33 > 0:56:37Carbon dioxide and water in our atmosphere gives us just the right
0:56:37 > 0:56:38greenhouse effect.
0:56:38 > 0:56:41Venus has too much greenhouse effect.
0:56:41 > 0:56:43Mars doesn't have enough.
0:56:43 > 0:56:47We're also the right distance from our star.
0:56:47 > 0:56:51We're just far enough away from the sun that we are not too hot,
0:56:51 > 0:56:54but we're close enough that we're not too cold.
0:56:54 > 0:56:58The temperature is perfect for water to exist in all three conditions
0:56:58 > 0:57:01and that is so vital for life to have developed
0:57:01 > 0:57:03and evolved on this planet.
0:57:03 > 0:57:07And the Earth even spins in the right way.
0:57:07 > 0:57:10So the other thing that makes Earth such a great place to live
0:57:10 > 0:57:14is that it spins on its axis every 24 hours,
0:57:14 > 0:57:18so the day and night temperatures never get super extreme.
0:57:18 > 0:57:23So our planet has the right unique combination of things to make it
0:57:23 > 0:57:27just the right place for life to have developed and maintained itself
0:57:27 > 0:57:28for billions of years.
0:57:32 > 0:57:36For thousands of years, we've gazed up at the night sky,
0:57:36 > 0:57:38wondering what other planets might be like.
0:57:40 > 0:57:44Astronomers began by studying our own solar system.
0:57:44 > 0:57:48Now they are exploring the wider universe and can even study
0:57:48 > 0:57:51the weather on planets hundreds of light years away.
0:57:53 > 0:57:58They have discovered climates and weather stranger than fiction -
0:57:58 > 0:58:01alien worlds with extreme temperatures,
0:58:01 > 0:58:04bizarre clouds and even ruby rain.
0:58:08 > 0:58:12But they've yet to find another planet like Earth,
0:58:12 > 0:58:15with weather that is suitable for life,
0:58:15 > 0:58:17that's not too hot or too cold.
0:58:19 > 0:58:20So, for the time being,
0:58:20 > 0:58:25it looks like a warm and pleasant day on Earth with a gentle breeze
0:58:25 > 0:58:26and a slight risk of rain
0:58:26 > 0:58:29might actually be the weirdest weather of them all.