0:00:00 > 0:00:00- *
0:00:02 > 0:00:06- Could there be life - anywhere else in the cosmos?
0:00:06 > 0:00:10- It's a big question. - Is there life beyond earth?
0:00:10 > 0:00:12- If so, what sort of life is it?
0:00:14 > 0:00:18- Of the 50 billion sun-like stars - in our galaxy...
0:00:18 > 0:00:22- ..one in five should have planets - warm enough for life.
0:00:25 > 0:00:28- The odds are better than - winning the lottery.
0:00:28 > 0:00:33- There are many planets which - could sustain life in the universe.
0:00:34 > 0:00:35- Which one has life on it?
0:00:37 > 0:00:40- Other planets like the earth - that are home to life?
0:00:41 > 0:00:44- This programme will reveal - they do exist.
0:00:58 > 0:01:03- Astronomers knew of just one star - with orbiting planets 20 years ago.
0:01:04 > 0:01:06- Our star - the sun.
0:01:07 > 0:01:11- In the 1990s, - we thought planets were rare things.
0:01:11 > 0:01:13- But no, they're very common.
0:01:14 > 0:01:16- If you look at a star in the sky...
0:01:16 > 0:01:19- ..it's likely - there's a planet orbiting it.
0:01:21 > 0:01:26- Astronomers discovered a new planet - in 1995 - 51 Pegasi b.
0:01:30 > 0:01:35- It was similar to Jupiter, - but 50 light years from the earth.
0:01:41 > 0:01:44- It was the very first exoplanet - to be found.
0:01:45 > 0:01:50- And after finding one, - scientists wanted to find more.
0:01:55 > 0:01:57- I'd say we're in the golden age.
0:01:57 > 0:02:01- Go back 20 years - and we knew of no exoplanets.
0:02:01 > 0:02:04- We found the first one in 1995.
0:02:04 > 0:02:07- Over 1,000 have now been discovered.
0:02:07 > 0:02:11- It's certainly one of the most - exciting areas in astronomy.
0:02:14 > 0:02:19- The vast majority of exoplanets were - discovered in the last four years...
0:02:20 > 0:02:23- ..thanks to a telescope - called Kepler.
0:02:25 > 0:02:28- Things started to change - 15 years ago.
0:02:28 > 0:02:33- Launching the Kepler space telescope - transformed everything.
0:02:38 > 0:02:43- Kepler looks for shadows - in front of distant stars.
0:02:43 > 0:02:46- A shadow means a planet - has just crossed in front it.
0:02:49 > 0:02:55- When a plant orbits a star, and that - orbit points straight at us...
0:02:57 > 0:03:00- ..the planet will move - in front of the star...
0:03:00 > 0:03:03- ..and there will be - a tiny dip in the light.
0:03:07 > 0:03:09- Kepler can find planets...
0:03:09 > 0:03:12- ..but it can't tell - what kind of planets they are.
0:03:18 > 0:03:23- To find out, astronomers turn to the - most powerful telescopes on earth.
0:03:30 > 0:03:34- It's nine o clock at night - in Berkeley, California.
0:03:36 > 0:03:39- Astronomer, Geoff Marcy's day - is just beginning.
0:03:40 > 0:03:44- Tonight, he'll control - the Keck telescope in Hawaii...
0:03:45 > 0:03:49- ..to look at the hundreds of new - exoplanets discovered by Kepler.
0:03:51 > 0:03:53- Carolyn is there, - in the lower panel.
0:03:54 > 0:03:56- She's at the Keck headquarters...
0:03:56 > 0:04:00- ..at 2,000 feet up the flanks - of the Mauna Kea volcano.
0:04:03 > 0:04:05- We give her - the coordinates of the stars...
0:04:07 > 0:04:11- ..then she points the Keck telescope - at each one of the stars.
0:04:11 > 0:04:14- That should be the - centre of the slit there.
0:04:14 > 0:04:18- That looks beautiful right there. - We are ready to begin.
0:04:18 > 0:04:21- The first star of the night - - first exposure.
0:04:22 > 0:04:26- Keck measures how planets - are influenced by their stars.
0:04:28 > 0:04:32- Measuring the gravitational pull - between both...
0:04:32 > 0:04:34- ..gives Geoff valuable clues.
0:04:36 > 0:04:39- What we'd really, - dearly love to know...
0:04:40 > 0:04:44- ..is are the planets like the earth, - with a hard surface...
0:04:44 > 0:04:48- ..where water puddles and advanced - technological species can walk...
0:04:48 > 0:04:54- ..or are the planets a dud gas giant - not suitable for life as we know it?
0:04:55 > 0:04:56- If a planet is rocky...
0:04:57 > 0:05:00- ..Geoff calculates - how far it orbits from its sun.
0:05:01 > 0:05:06- He's looking for the Goldilocks Zone - - not too hot and not too cold.
0:05:09 > 0:05:14- This planet's location is important - because it's in the Goldilocks Zone.
0:05:16 > 0:05:18- It's far enough from the sun...
0:05:18 > 0:05:23- ..so that its energy doesn't turn - the water into steam and vanish...
0:05:24 > 0:05:27- ..but close enough - that water remains unfrozen.
0:05:28 > 0:05:31- Water in liquid form - is crucial for life.
0:05:32 > 0:05:36- We used to think - the earth's distance from the Sun...
0:05:36 > 0:05:39- ..defined the habitable zones.
0:05:40 > 0:05:44- A few decades ago, - scientists were confident...
0:05:44 > 0:05:48- ..that there could be life - on planets such as Venus and Mars.
0:05:51 > 0:05:56- But Venus is too hot - and Mars is too cold.
0:05:58 > 0:06:01- So it seemed - that the distance needed...
0:06:01 > 0:06:06- ..between a planet and its sun to - sustain any life was very limited.
0:06:11 > 0:06:15- Since discovering exoplanets, - scientists now believe...
0:06:15 > 0:06:19- ..that the distance - between a planet and its star...
0:06:19 > 0:06:24- ..is not the only factor to - determine if it can sustain life.
0:06:26 > 0:06:30- Planets far from their sun - can be heated by greenhouse gases...
0:06:30 > 0:06:32- ..such as carbon dioxide.
0:06:37 > 0:06:42- Planets orbiting much closer to - their sun can avoid overheating...
0:06:43 > 0:06:46- ..if their surface is pale - and highly reflective.
0:06:46 > 0:06:52- The zone that could sustain life is - much wider than originally thought.
0:06:57 > 0:07:01- After a few years of searching, - the Kepler and Keck telescopes...
0:07:02 > 0:07:05- ..have made - some astonishing discoveries.
0:07:07 > 0:07:10- Using a tiny patch of sky, - they calculated...
0:07:10 > 0:07:15- ..how many habitable planets could - be in our galaxy - the Milky Way.
0:07:20 > 0:07:24- Geoff and his PhD student, - Eric Petigura have the answer.
0:07:24 > 0:07:27- It's big news.
0:07:31 > 0:07:34- Good morning. - Welcome to the Kepler news briefing.
0:07:35 > 0:07:36- First, Eric Petigura.
0:07:37 > 0:07:40- Today, I'm happy to report - that 22% of sun-like stars...
0:07:41 > 0:07:43- ..harbour a planet - in the habitable zone.
0:07:44 > 0:07:48- That is, a planet that's between one - and two times the size of earth...
0:07:48 > 0:07:52- ..and is bathed in a similar amount - of stellar intensity.
0:07:55 > 0:07:57- It's a historic announcement.
0:07:58 > 0:08:03- There are around 11 billion - potentially habitable worlds...
0:08:03 > 0:08:04- ..in the Milky Way.
0:08:16 > 0:08:20- I'm old enough to remember - man walking on the moon.
0:08:21 > 0:08:25- I've lived through - many of these historical events...
0:08:25 > 0:08:29- ..but I must admit, - launching Kepler really was special.
0:08:30 > 0:08:32- We're finding many more planets.
0:08:33 > 0:08:36- We're bound to find life - on one of these planets.
0:08:40 > 0:08:44- And we now know the best place - to find alien life.
0:08:47 > 0:08:50- Kepler-62, - a star system with five planets.
0:08:51 > 0:08:57- They're rocky, like the earth, and - they're within the Goldilocks Zone.
0:08:57 > 0:09:02- What's interesting is that life - could be sustained there.
0:09:04 > 0:09:08- What's special is that it's only - 10% bigger than the earth...
0:09:08 > 0:09:12- ..and it's right in the middle - of the Goldilocks Zone.
0:09:16 > 0:09:21- Exoplanet 62F lies on the - outer edge of the Kepler-62 system.
0:09:23 > 0:09:26- This far out, - water would be locked in ice.
0:09:27 > 0:09:29- But if 62f has an atmosphere...
0:09:30 > 0:09:34- ..the greenhouse effect - may have melted enough water...
0:09:35 > 0:09:39- ..to create puddles, - where simple life can thrive.
0:09:45 > 0:09:47- Its sister planet 62e - is very different.
0:09:54 > 0:09:56- Sitting closer to its sun...
0:09:57 > 0:10:01- ..astronomers believe - there's a potential paradise here.
0:10:03 > 0:10:08- Warm waters break on golden sands, - basking in tropical temperatures.
0:10:12 > 0:10:16- On earth, in similar conditions, - life thrives.
0:10:24 > 0:10:29- Kepler-62 is exciting because it's - so similar to our own solar system.
0:10:33 > 0:10:36- But does alien life - need a sun-like star to survive?
0:10:37 > 0:10:39- Does it even need a planet?
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0:10:46 > 0:10:46- Subtitles
0:10:46 > 0:10:48- Subtitles- - Subtitles
0:10:55 > 0:11:00- Astronomers believe there may be - 11 billion exoplanets in our galaxy.
0:11:03 > 0:11:08- A quarter of these exoplanets - orbit sun-like stars.
0:11:10 > 0:11:14- But there's more than one - type of sun in the cosmos.
0:11:16 > 0:11:20- Recently, astronomers - have been looking for planets...
0:11:21 > 0:11:25- ..orbiting a special kind of star, - called a red dwarf.
0:11:26 > 0:11:28- What we're seeing here...
0:11:29 > 0:11:33- ..is an image of our sun - taken a few hours ago.
0:11:33 > 0:11:37- Right over here, - we have an artistic impression...
0:11:37 > 0:11:39- ..of a red dwarf star.
0:11:42 > 0:11:45- From earth, - red dwarfs are so small and dim...
0:11:45 > 0:11:48- ..they're invisible - to the naked eye.
0:11:49 > 0:11:53- But if you could see them, - the sky would look like this.
0:11:55 > 0:11:59- Red dwarfs outnumber other stars - by three to one...
0:11:59 > 0:12:03- ..and they have a lot of - earth-sized planets orbiting them.
0:12:04 > 0:12:07- There are billions - of these red dwarfs.
0:12:07 > 0:12:09- Tens of billions of them.
0:12:10 > 0:12:13- The number of planets out there - is huge.
0:12:17 > 0:12:20- Red dwarfs often sustain - a number of planets...
0:12:21 > 0:12:23- ..the same size as the earth.
0:12:24 > 0:12:26- And they're easy to find.
0:12:29 > 0:12:34- If you looked for the eclipse of a - planet across the face of a star...
0:12:35 > 0:12:39- ..you can see that this blocks - a much larger, fractional area...
0:12:40 > 0:12:43- ..of the surface of the Red Dwarf, - causing a much larger signal...
0:12:44 > 0:12:48- ..making small planets - easier to detect around small stars.
0:12:51 > 0:12:54- The orbits - of these earth-like planets...
0:12:54 > 0:12:57- ..come with a crucial difference.
0:12:57 > 0:13:02- We think our solar system is huge - and, of course, it is.
0:13:02 > 0:13:05- But if our sun was changed - to a red dwarf...
0:13:05 > 0:13:08- ..the planets - would orbit much quicker.
0:13:10 > 0:13:13- A year would take weeks - rather than months.
0:13:18 > 0:13:23- For a planet to be habitable here, - it has to be closer to its star.
0:13:23 > 0:13:27- Red dwarfs radiate far less energy - than our sun...
0:13:27 > 0:13:30- ..and the Goldilocks Zone - is much smaller.
0:13:35 > 0:13:40- The surface of a red dwarf planet - would be red and dull.
0:13:42 > 0:13:46- In the sky, the other planets - would be seen clearly.
0:13:48 > 0:13:52- Some would appear eight times - as large as our own moon...
0:13:54 > 0:13:57- ..and race across the sky, - from horizon to horizon...
0:13:58 > 0:13:59- ..in less than an hour.
0:14:02 > 0:14:07- There may be billions of exoplanets - just like this one in our Milky Way.
0:14:11 > 0:14:16- For every earth-like planet - receiving yellow light from a sun...
0:14:16 > 0:14:20- ..there are two more, - bathed in the glow of a red dwarf.
0:14:30 > 0:14:35- We knew of only one - habitable planet 20 years ago.
0:14:36 > 0:14:39- That number could now be 33 billion.
0:14:42 > 0:14:46- Five planets for every man, woman - and child on earth.
0:14:48 > 0:14:50- And there could be even more.
0:14:55 > 0:14:58- We now have the technology...
0:14:58 > 0:15:03- ..which allows us to find the moons - orbiting the planets.
0:15:09 > 0:15:13- Astronomers are looking beyond - just planets for signs of life.
0:15:14 > 0:15:17- Moons are also being examined.
0:15:20 > 0:15:25- Many of them are like Jupiter, - where life isn't really possible.
0:15:26 > 0:15:30- But the moons orbiting - distant planets, known as exomoons.
0:15:35 > 0:15:39- In the future, we may focus our - efforts on these exomoons.
0:15:44 > 0:15:49- And the biggest of these exomoons - could resemble our earth.
0:15:52 > 0:15:58- These exomoons could be just rocks - or places where water has frozen.
0:15:59 > 0:16:04- They could be places where there's - an atmosphere with water as liquid.
0:16:05 > 0:16:07- All sorts of environments...
0:16:07 > 0:16:13- ..depending on how far exomoons are - from the star their planet orbits.
0:16:15 > 0:16:17- To search for exomoons...
0:16:17 > 0:16:22- ..astronomers look for double dips - in the brightness of distant stars.
0:16:24 > 0:16:29- When we look at the data from Kepler - we can we see the planets.
0:16:30 > 0:16:36- If there are exomoons orbiting the - exoplanets, it's the same principle.
0:16:37 > 0:16:39- We can see their shadows.
0:16:46 > 0:16:50- Despite these moons being - millions of miles from their sun...
0:16:51 > 0:16:56- ..they could sustain life, - because of the moon's geology.
0:16:58 > 0:17:02- Some of these moons - are in very cold places...
0:17:02 > 0:17:07- ..but because there are other large - moons pulling on them, they stretch.
0:17:08 > 0:17:11- Heat is then produced - inside these moons.
0:17:17 > 0:17:20- Moons tend to orbit - in elliptical paths...
0:17:21 > 0:17:25- ..so the distance from their planet - changes over time.
0:17:27 > 0:17:32- When the moon is close, gravity can - literally raise the landscape.
0:17:36 > 0:17:40- This generates frictional heat - in the core of the moon.
0:17:41 > 0:17:44- Heat that could be sufficient - to sustain life.
0:17:46 > 0:17:49- The moon does not rely on a star - for its heat.
0:17:52 > 0:17:56- These small moons - are so close to larger planets...
0:17:56 > 0:17:58- ..they are pulled by gravity.
0:18:00 > 0:18:05- This friction which comes - from that generates energy.
0:18:05 > 0:18:09- Energy that could possibly be enough - to sustain life.
0:18:14 > 0:18:16- From these exomoons...
0:18:16 > 0:18:21- ..we could see some of the most - spectacular sights in the universe.
0:18:23 > 0:18:26- Imagine a warm, rocky world - just like our own...
0:18:26 > 0:18:30- ..with oceans, mountains - and weather systems.
0:18:32 > 0:18:34- In the sky, a massive - ringed planet...
0:18:35 > 0:18:40- ..and a fiery moon - shooting hot magma into space.
0:18:41 > 0:18:45- It's just like a scene - from science fiction.
0:18:45 > 0:18:48- There's bound to be - exomoons out there...
0:18:49 > 0:18:52- ..orbiting ringed planets - like our Jupiter.
0:18:54 > 0:18:58- If you were on one of these moons, - you'd see a ringed planet...
0:18:58 > 0:19:00- ..with one, if not two, stars.
0:19:00 > 0:19:04- We know of exoplanets - which orbit more than one star.
0:19:04 > 0:19:08- In sci-fi, you see planets - with two stars - two suns.
0:19:11 > 0:19:13- That could be a reality.
0:19:16 > 0:19:19- So the fantasy could come true.
0:19:19 > 0:19:24- We see in fiction and in films - like Avatar amazing worlds on moons.
0:19:26 > 0:19:31- A few decades ago our imaginations - were focused on planets...
0:19:31 > 0:19:33- ..but now things have moved on.
0:19:40 > 0:19:43- We now know - that our world is not unique.
0:19:48 > 0:19:53- There are tens of billions of - planets orbiting stars like our sun.
0:19:55 > 0:19:58- Planets that could sustain life.
0:20:03 > 0:20:07- If life is out there, how do we - find it, when it's so far away?
0:20:09 > 0:20:11- These planets are so far away.
0:20:11 > 0:20:16- The problem is we can't go there - to discover if life exists.
0:20:21 > 0:20:25- Even the closest habitable planet - is too far.
0:20:27 > 0:20:30- Voyager 1, our fastest - space probe...
0:20:30 > 0:20:33- ..would take over 200,000 years - to reach it.
0:20:38 > 0:20:40- To find alien life in our galaxy...
0:20:41 > 0:20:45- ..we need something that moves - at the speed of light.
0:20:48 > 0:20:52- So that's what astronomers - are using - starlight.
0:20:59 > 0:21:03- Astronomers realized - we could split the light of stars...
0:21:03 > 0:21:05- ..into its rainbow - constituent colours...
0:21:06 > 0:21:08- ..and study the properties - of material in those stars.
0:21:10 > 0:21:14- This is the rainbow of light, - coming from our own sun.
0:21:15 > 0:21:20- The black marks, called absorption - lines, create a unique signature.
0:21:22 > 0:21:27- They tell scientists what chemicals - are in the sun's atmosphere.
0:21:29 > 0:21:32- Like human fingerprints that are - specific to each person...
0:21:32 > 0:21:37- ..the chemical fingerprints - - those dark absorption lines...
0:21:37 > 0:21:41- ..tell us an amazing amount - about the make-up of that object.
0:21:46 > 0:21:50- If we can discover the chemical - make-up of a star's atmosphere...
0:21:51 > 0:21:53- ..we can do the same with planets.
0:21:57 > 0:22:00- Some are clear signs of life, - called biosignatures.
0:22:03 > 0:22:07- The most important biosignature - is oxygen.
0:22:07 > 0:22:11- If we find oxygen, - there's a chance of finding life.
0:22:11 > 0:22:13- Oxygen reacts with so much...
0:22:14 > 0:22:18- ..it would disappear - if nothing was there to produce it.
0:22:18 > 0:22:22- If oxygen is present, - more complex life could be present.
0:22:23 > 0:22:24- But there's a problem.
0:22:25 > 0:22:30- Examining light from a distant star - is relatively easy...
0:22:30 > 0:22:34- ..but searching for oxygen - on a distant exoplanet...
0:22:34 > 0:22:36- ..is far more difficult.
0:22:39 > 0:22:43- What we're trying to do - is to find a light from a match...
0:22:44 > 0:22:47- ..next to a bright spotlight.
0:22:47 > 0:22:51- We must hide the light - that comes from the star.
0:22:51 > 0:22:56- Only then can we see - reflected light from the planet.
0:23:00 > 0:23:04- To overcome this problem, - scientists and engineers...
0:23:04 > 0:23:07- ..came up with an audacious plan - - the Starshade.
0:23:17 > 0:23:22- This vast space umbrella would open - in front of a robotic telescope...
0:23:22 > 0:23:25- ..and block the glare - of distant stars.
0:23:27 > 0:23:31- If it works, we'll be able to peer - at earth-sized exoplanets...
0:23:32 > 0:23:33- ..for the first time.
0:23:40 > 0:23:44- If we can see the light from a small - planet next to a bright star...
0:23:45 > 0:23:46- ..it would be amazing.
0:23:47 > 0:23:50- We could then study - these distant planets...
0:23:51 > 0:23:56- ..using the same methods used for - planets in our own solar system...
0:23:56 > 0:23:58- ..and learn more about them.
0:24:01 > 0:24:04- But more work - needs to be done on the Starshade.
0:24:05 > 0:24:08- After years of delay, - a new team has taken over.
0:24:09 > 0:24:14- It hopes to take the first ever - picture of an earth-like exoplanet.
0:24:14 > 0:24:18- Today, NASA engineers - are testing the mechanism...
0:24:18 > 0:24:22- ..that will open the delicate petals - of the Starshade.
0:24:23 > 0:24:25- This truss - becomes the size of a house.
0:24:26 > 0:24:29- Each of the 60 points - must be located...
0:24:29 > 0:24:32- ..to within a 20,000th of an inch.
0:24:32 > 0:24:36- This is our third time. - We change it each time.
0:24:36 > 0:24:38- Things happen - that we didn't expect.
0:24:38 > 0:24:41- Some of those things will happen - as we deploy it now!
0:24:44 > 0:24:48- The engineers watch - as the petals open.
0:24:59 > 0:25:04- One snagged tape would be enough - to throw the petals out of position.
0:25:11 > 0:25:15- As each strut tightens, - the team is nearly there.
0:25:20 > 0:25:21- Well done, everybody!
0:25:21 > 0:25:22- Well done, everybody!- - Good job, David.
0:25:24 > 0:25:28- If all goes well, Starshade - will be launched into space...
0:25:28 > 0:25:33- ..perhaps giving the world its first - glimpse of a living exoplanet.
0:25:34 > 0:25:36- When we get that first image...
0:25:37 > 0:25:41- ..on the front page of newspapers, - it'll be like the moon landing.
0:25:41 > 0:25:43- The entire world will say, "Wow!"
0:25:44 > 0:25:49- We'll finally answer the question - - is there life on another planet?
0:25:49 > 0:25:54- To find that no life has developed - elsewhere in the universe...
0:25:54 > 0:25:56- ..would be a shock.
0:25:56 > 0:26:00- It would be very sad to discover - that we are alone.
0:26:03 > 0:26:08- When we get the picture of a living - exoplanet, another question remains.
0:26:09 > 0:26:12- What will alien life be like?
0:26:21 > 0:26:21- .
0:26:26 > 0:26:26- Subtitles
0:26:26 > 0:26:28- Subtitles- - Subtitles
0:26:36 > 0:26:41- Our galaxy is full of planets and - moons that are similar to earth...
0:26:42 > 0:26:45- ..with rocky shorelines - and warm oceans.
0:26:47 > 0:26:51- One question remains - - is there life here?
0:26:51 > 0:26:54- We've found planets like ours.
0:26:55 > 0:26:57- The next question is...
0:26:57 > 0:27:02- ..if these planets are similar - to earth, is there life on them?
0:27:08 > 0:27:10- What would this alien life be like?
0:27:11 > 0:27:13- Clues lie in our early history.
0:27:21 > 0:27:26- Four and a half billion years ago, - the earth is created.
0:27:30 > 0:27:34- Over billions of years, - the earth was literally on fire.
0:27:36 > 0:27:39- Giant asteroids - smashed into its surface.
0:27:45 > 0:27:47- Finally, it stops.
0:27:49 > 0:27:52- The earth becomes cool enough - for solid rock to form.
0:27:53 > 0:27:55- Then, something miraculous happens.
0:27:57 > 0:28:03- We now know that life appears on - earth almost as soon as it cools.
0:28:09 > 0:28:13- All life on earth, - animal or plant...
0:28:14 > 0:28:17- ..relies on the same - basic chemistry.
0:28:19 > 0:28:21- Long strands of DNA...
0:28:24 > 0:28:29- ..made up from chemicals like - carbon, hydrogen and phosphorus.
0:28:32 > 0:28:38- Through telescopes, scientists found - the basic ingredients for life...
0:28:39 > 0:28:44- ..in asteroids, - in clouds of gas and in stars.
0:28:54 > 0:28:58- Most of the universe - is made of similar material.
0:28:59 > 0:29:03- We look at other planets - and see the organic chemicals...
0:29:03 > 0:29:06- ..which led to biochemistry - on earth.
0:29:10 > 0:29:15- It takes one additional ingredient - to turn chemistry into biochemistry.
0:29:16 > 0:29:17- Life relies on water.
0:29:18 > 0:29:22- Water is the most important molecule - for life.
0:29:23 > 0:29:28- Molecular biologists say DNA is - the most important factor. Rubbish!
0:29:29 > 0:29:32- Other molecules can replace DNA - but water is unique.
0:29:33 > 0:29:36- Water melts almost everything.
0:29:36 > 0:29:40- It determines - how other molecules come together.
0:29:40 > 0:29:44- Things like proteins and enzymes.
0:29:46 > 0:29:50- Water is so powerful, it can - nurture life in extreme places...
0:29:51 > 0:29:53- ..like Mono Lake in California.
0:29:54 > 0:29:59- This water, three times saltier - than the sea...
0:29:59 > 0:30:03- ..is so alkaline - it can burn through clothing.
0:30:06 > 0:30:12- Mono Lake should be dead, - yet bacteria and life thrive here.
0:30:14 > 0:30:18- Astrobiologists - study extreme habitats like this...
0:30:18 > 0:30:23- ..to understand where else - in the galaxy life could exist.
0:30:23 > 0:30:28- By looking at those environments, - we can map out the limits of life.
0:30:28 > 0:30:31- How cold, how hot how salty, - what range of pH.
0:30:31 > 0:30:35- By mapping out those limits, - we have a guide book...
0:30:35 > 0:30:38- ..for how to search for life - on other worlds.
0:30:38 > 0:30:41- When we talk about - what's possible...
0:30:41 > 0:30:45- ..we fall back on Darwin's ideas - and what has evolved.
0:30:45 > 0:30:49- Life evolved to suit its environment - not the other way around.
0:30:52 > 0:30:57- If distant exoplanets have liquid - water, they could also have life.
0:30:57 > 0:30:58- But what sort of life?
0:30:59 > 0:31:01- I think, if alien life exists...
0:31:02 > 0:31:05- ..it would look similar - to life as we know it.
0:31:09 > 0:31:14- We make an educated guess - by looking at these distant worlds.
0:31:14 > 0:31:18- On red dwarf stars, plant life - may be purple, not green...
0:31:19 > 0:31:24- ..to extract the maximum amount - of energy from the dim red light.
0:31:27 > 0:31:31- Sci-fi suggests - weird-looking monsters...
0:31:31 > 0:31:35- ..but the truth is, - we could all look the same.
0:31:40 > 0:31:46- Evolution on earth favours similar - shapes in similar environments.
0:31:50 > 0:31:53- In water, it's easy to mistake - a dolphin for a shark...
0:31:54 > 0:31:58- ..even though one is a mammal - and the other is a fish.
0:31:59 > 0:32:02- On another planet, - the basic shapes would be similar.
0:32:03 > 0:32:07- It's likely that the same physics - and chemistry in the universe...
0:32:08 > 0:32:11- ..will lead to - a similar kind of evolution.
0:32:11 > 0:32:14- We may not see birds or fish - on other planets...
0:32:14 > 0:32:17- ..but the same rules - govern evolution.
0:32:20 > 0:32:25- Exoplanets are so far away it may be - hundreds or thousands of years...
0:32:25 > 0:32:29- ..before we're able to see an alien - face to face.
0:32:32 > 0:32:35- But we may hear from them - much sooner than that.
0:32:42 > 0:32:46- In Northern California, - 42 satellite dishes scan the sky...
0:32:46 > 0:32:49- ..hoping to hear ET phone home.
0:32:51 > 0:32:54- Seth Shostak is - the senior astronomer for SETI...
0:32:55 > 0:32:59- ..the Search For Extraterrestrial - Intelligence.
0:33:01 > 0:33:07- He believes alien civilizations may - be sending radio waves into space...
0:33:07 > 0:33:12- ..and the Allen Telescope Array - listens for them, day and night.
0:33:13 > 0:33:17- When you think of finding - intelligent life beyond earth...
0:33:17 > 0:33:21- ..aliens, as they're known, there - are many approaches you could take.
0:33:21 > 0:33:25- You could try and go there, - but they're light years away.
0:33:25 > 0:33:28- We could wait for them - to land in the back yard.
0:33:28 > 0:33:30- A lot of people - are convinced that they have.
0:33:31 > 0:33:34- We try and pick up - radio signals or light signals.
0:33:34 > 0:33:37- Something that allows us - to find them at home.
0:33:44 > 0:33:48- Radio waves are the best means - for cosmic communication.
0:33:50 > 0:33:53- They're easy to create - and very powerful.
0:33:58 > 0:34:01- Radio waves - can punch through vast clouds...
0:34:02 > 0:34:05- ..and carry huge amounts - of information.
0:34:09 > 0:34:12- Best of all, - they travel at the speed of light.
0:34:15 > 0:34:20- The idea is to listen out for Radio - Cymru coming from another planet!
0:34:21 > 0:34:24- If there is - intelligent life out there...
0:34:24 > 0:34:28- ..they're bound to have - telecommunication systems...
0:34:29 > 0:34:34- ..and radio broadcasts must be - happening all over the universe.
0:34:35 > 0:34:39- This big reflector picks up signals - that are coming from space...
0:34:40 > 0:34:41- ..assuming there are any...
0:34:41 > 0:34:45- ..and it reflects them back - to this secondary reflector.
0:34:45 > 0:34:47- That then bounces them back inside.
0:34:47 > 0:34:52- Inside, this is where the rubber - meets the road - it's the receiver.
0:34:53 > 0:34:57- It looks like some sort of death ray - but that's because it's sensitive...
0:34:57 > 0:35:00- ..and can amplify a wide range - of radio frequencies...
0:35:01 > 0:35:04- ..from low ones, like 1GHz, - to high ones, near 12GHz.
0:35:04 > 0:35:10- Amplified signals go out through - a fibre optic running underground...
0:35:10 > 0:35:13- ..to the control room, - where they're analysed.
0:35:14 > 0:35:18- If we find ET, we book a flight to - Stockholm and we collect a prize.
0:35:19 > 0:35:23- To increase his chances - of finding an alien signal...
0:35:23 > 0:35:28- ..Seth and chief engineer Chris - Munson discuss a dish upgrade...
0:35:28 > 0:35:31- ..to allow them - to scan deeper into space.
0:35:36 > 0:35:39- Tomorrow, we'll install - this antenna to your left.
0:35:40 > 0:35:43- If all goes well, - we'll have this telescope...
0:35:43 > 0:35:47- ..standing up and singing - within eight to nine months.
0:35:48 > 0:35:52- We'll be comparable to the best - radio telescopes in the world.
0:35:53 > 0:35:55- Twice the sensitivity.
0:35:55 > 0:35:59- ET can be 40% further away - and we'd still hear him.
0:36:00 > 0:36:03- SETI is an extremely clever idea.
0:36:03 > 0:36:07- In the days before we were able to - send probes into space...
0:36:07 > 0:36:10- ..to look at our nearby planets - and moons...
0:36:11 > 0:36:15- ..all we could do was hope somebody - out there would send us a message...
0:36:16 > 0:36:20- ..saying, "Yes we're here! - May we have your attention?"
0:36:24 > 0:36:27- So far, SETI hasn't heard a peep.
0:36:27 > 0:36:33- Astronomers remain optimistic, - but time is not on their side.
0:36:36 > 0:36:41- In another 50 years, SETI will have - surveyed the entire night sky...
0:36:41 > 0:36:44- ..and silence - would be a major setback.
0:36:46 > 0:36:49- If it makes sense - to try and eavesdrop on ET...
0:36:50 > 0:36:52- ..this will work before mid-century.
0:36:52 > 0:36:55- If it hasn't worked - by mid-century...
0:36:55 > 0:36:58- ..they're not out there, - they're not using radio...
0:36:58 > 0:37:01- ..or you're doing - the wrong experiment.
0:37:01 > 0:37:04- If this is going to work, - it's going to work soon.
0:37:05 > 0:37:08- There are other ways - of looking for intelligent life.
0:37:11 > 0:37:14- If there's life - on more than one planet...
0:37:14 > 0:37:19- ..it's possible they use lasers to - communicate from planet to planet.
0:37:22 > 0:37:27- Geoff Marcy thinks it's possible - to pick up these laser signals...
0:37:27 > 0:37:31- ..using giant optical telescopes - like Keck.
0:37:32 > 0:37:35- This is a star - that has two planets...
0:37:35 > 0:37:40- ..this second orbiting the star - lined up with us at the earth.
0:37:40 > 0:37:44- If there's any radio communication - or laser communication...
0:37:45 > 0:37:48- ..between the colony on one planet - and the other planet...
0:37:49 > 0:37:53- ..we hope to pick up the - communication between the planets...
0:37:53 > 0:37:56- ..as spillover - that we eavesdrop on.
0:38:00 > 0:38:05- No laser signals tonight but - who knows what tomorrow will bring.
0:38:08 > 0:38:10- If ET does call, what next?
0:38:14 > 0:38:15- Do we reply?
0:38:16 > 0:38:19- And what do we say? - In what language?
0:38:21 > 0:38:26- Do we tell them about our - traditions, cultures and science?
0:38:30 > 0:38:33- You'd send them - a lot of information.
0:38:33 > 0:38:35- If they're 100 light years away...
0:38:36 > 0:38:39- ..it takes 100 years - for the signal to get there...
0:38:39 > 0:38:43- ..and another 100 years - for the response to come back.
0:38:43 > 0:38:45- You'd send it all at once.
0:38:45 > 0:38:47- I'd send the Google Servers.
0:38:47 > 0:38:50- I would send the internet. - Let them figure it out.
0:38:53 > 0:38:58- Right now, ET's not talking, - at least not on our frequency.
0:38:59 > 0:39:02- We could be listening - for the wrong things.
0:39:05 > 0:39:09- Or should we face the possibility - there's nobody out there?
0:39:09 > 0:39:11- Are we alone?
0:39:15 > 0:39:15- .
0:39:21 > 0:39:21- Subtitles
0:39:21 > 0:39:23- Subtitles- - Subtitles
0:39:31 > 0:39:33- The question remains unanswered.
0:39:34 > 0:39:38- Are we alone in the cosmos?
0:39:38 > 0:39:40- There's no shortage of planets.
0:39:41 > 0:39:44- They're being found - on a weekly basis.
0:39:47 > 0:39:48- In ten years...
0:39:49 > 0:39:54- ..we've gone from knowing about one - planet beyond our solar system...
0:39:54 > 0:39:56- ..to thousands.
0:39:56 > 0:39:58- So there's the first tick.
0:39:58 > 0:40:03- The next question, - is there life on these planet?
0:40:05 > 0:40:08- Despite every effort, - there's no sign of life.
0:40:11 > 0:40:14- After a 50-year search - using the latest technology...
0:40:15 > 0:40:17- ..not a single signal - has been heard.
0:40:20 > 0:40:24- We've searched for - extraterrestrial life for decades.
0:40:24 > 0:40:27- We've listened, - using radio and radar.
0:40:28 > 0:40:32- We've taken satellites - to look at our closest planets.
0:40:33 > 0:40:36- We're yet to find anything - on another planet.
0:40:37 > 0:40:40- It is possible we're alone here.
0:40:42 > 0:40:43- Something's not right.
0:40:44 > 0:40:49- Billions of planets ripe for life, - and not a single sign of life.
0:40:54 > 0:40:58- The universe is vast. - There should be life somewhere.
0:40:59 > 0:41:02- Why haven't they come to see us?
0:41:02 > 0:41:07- Maybe people on other planets - aren't of the same mindset as us.
0:41:07 > 0:41:10- They may like to stay - in the same place.
0:41:13 > 0:41:15- We have developed science.
0:41:16 > 0:41:20- On another planet, - they may concentrate on the arts.
0:41:20 > 0:41:26- They might spend all their time - painting and not looking at stars.
0:41:29 > 0:41:32- Imagine if the sky - was covered in clouds.
0:41:32 > 0:41:34- You may not see the stars.
0:41:34 > 0:41:37- If you don't know the stars exist...
0:41:37 > 0:41:42- ..you may think it would be - too boring to go beyond the clouds.
0:41:45 > 0:41:48- This conflict - is called the Fermi Paradox.
0:41:50 > 0:41:55- Some say the jump from simple life - to intelligent life is rare.
0:41:58 > 0:42:02- Our existence is a fluke - rather than the norm.
0:42:03 > 0:42:07- Are we the only intelligent beings - in the cosmos?
0:42:08 > 0:42:13- We may be a quirk, but this is - where we go back to statistics.
0:42:13 > 0:42:16- It's far more likely - that we're not a quirk.
0:42:18 > 0:42:22- People thought that because - we hadn't discovered other planets.
0:42:22 > 0:42:26- They thought we were a chance - in a million or a billion.
0:42:30 > 0:42:34- We are here because of a series - of cosmic coincidences.
0:42:35 > 0:42:39- Events unlikely to be repeated again - in precisely the same sequence.
0:42:40 > 0:42:41- Water, for example.
0:42:42 > 0:42:47- If the earth had received a fraction - more during its creation...
0:42:48 > 0:42:49- ..we wouldn't be here.
0:42:49 > 0:42:54- The quantity of water may have led - to the evolution of life on earth.
0:42:54 > 0:42:58- Too much water - and we wouldn't be here.
0:42:58 > 0:43:01- Too little, - and life couldn't be sustained.
0:43:02 > 0:43:07- We've been very lucky - to have just the right amount.
0:43:08 > 0:43:12- Considering - that delicate balance of water...
0:43:12 > 0:43:15- ..and the right amount of energy - from the sun...
0:43:15 > 0:43:19- ..we're looking at - a very small number of planets...
0:43:19 > 0:43:23- ..with the right conditions - to sustain life.
0:43:27 > 0:43:29- The right amount of water...
0:43:30 > 0:43:33- ..doesn't guarantee - the rise of intelligent life.
0:43:34 > 0:43:38- In four billion years of life - on earth, it's only happened once.
0:43:39 > 0:43:42- Had someone looked for life here - a million years ago...
0:43:43 > 0:43:46- ..they wouldn't have found - intelligent life.
0:43:51 > 0:43:55- For 200 million years, - dinosaurs ruled the earth.
0:43:55 > 0:44:00- Speed, strength and sharp teeth - were paramount...
0:44:01 > 0:44:05- ..rather than technology, science - and intelligence.
0:44:11 > 0:44:16- If a giant asteroid hadn't hit - the earth 65 million years ago...
0:44:17 > 0:44:21- ..dinosaurs might still - rule the earth.
0:44:26 > 0:44:28- There could be another answer.
0:44:28 > 0:44:31- It's possible alien life - existed and ended...
0:44:32 > 0:44:36- ..long before we had the technology - to find it.
0:44:38 > 0:44:41- And also what is intelligence?
0:44:46 > 0:44:52- We must look at a planet at the - right time to find intelligent life.
0:44:54 > 0:45:00- If we look too early, - it might not have developed.
0:45:00 > 0:45:04- If we look too late, - it could have died out.
0:45:10 > 0:45:12- Despite all the doubts...
0:45:13 > 0:45:18- ..scientists continue their search - for other civilizations.
0:45:18 > 0:45:20- The potential is there.
0:45:20 > 0:45:24- Our home is just one of billions - of pale blue dots...
0:45:24 > 0:45:26- ..with the potential for life.
0:45:28 > 0:45:30- It's likely we will find life...
0:45:30 > 0:45:33- ..somewhere in far reaches - of the universe.
0:45:34 > 0:45:37- It will transform our relationship - with the universe.
0:45:39 > 0:45:44- Scientists keep discovering new - places where life might flourish.
0:45:46 > 0:45:50- On worlds just like ours - and even on moons.
0:45:53 > 0:45:57- I'm hopeful, but I don't think - we'll find it in my lifetime.
0:45:58 > 0:46:03- But 20 years ago I didn't think we'd - find planets orbiting other stars.
0:46:06 > 0:46:10- All this raises questions - about our life here, on earth...
0:46:11 > 0:46:15- ..and about the possibility - of another life beyond the stars.
0:46:19 > 0:46:23- It's amazing how much we've learnt - in the past 20 years.
0:46:23 > 0:46:28- In another 20 years, we may talk - about life on some of these planets.
0:46:33 > 0:46:36- In the next century, - we'll find the answer.
0:46:37 > 0:46:39- Is there life beyond the earth?
0:46:42 > 0:46:45- I assume there is life - beyond the earth.
0:46:45 > 0:46:48- My frustration is - that I haven't seen it yet.
0:47:22 > 0:47:24- S4C subtitles by Eirlys A Jones
0:47:25 > 0:47:25- .