How the Universe Works (2010) s03e09 Episode Script

Second Earth

the earth is not alone in the last few years scientists have found that our planet is just one of billions out there in the Milky Way galaxy there's a really decent chance that there are more planets in the galaxy than there actually are stars we're now scouring these planets for evidence of atmospheres liquid water and life itself we are going to know where in the night sky you can point and find another earth we have a scientific method to actually determine whether there is life on another planet another earth alien life the truth is out there but are we ready for it the earth gives us the blueprint for life as we know it the Sun warms our oceans creating the perfect environment for all scales of life from the very smallest to the Giants that eat them Mountains Plains and forests teen with plant and animal species and it's all cocooned in a thick atmosphere that nurtures and protects for us it's paradise twenty years ago a group of scientists decided to find out if there were other paradises out there so-called exoplanets orbiting the stars that light up our night sky just in the last decade we've had this explosion and the discovery of these exoplanets which has revolutionized the whole field of astronomy the early days of exoplanet hunting turned up enormous jupiter-sized planets by the boatload these hot gas each iins proved easy to find but hostile to life as we know it now though new telescopes and technologies have allowed astronomers to target smaller planets earth-sized ones and the stunning results have transformed the way we see our place in the universe we now know something precious that our planet Earth is not unique it's not even rare there are tons hoards flocks if you will of other earth-like planets out there fluttering around the other stars some stars probably have multiple earths orbiting them that's how common earth-like planets are we owe this exoplanet explosion to a Space Telescope called Kepler the Kepler space telescope is an observatory in space that is staring at one spot in the sky it's looking at roughly 150,000 stars and it's looking for the tell-tale sign of planets orbiting those stars then every time the planet passes in front of the star it'll block a little bit of that star light and if you plot the amount of light you get from the star it drops and then goes back up as the planet passes in just four years scientists have detected over a thousand exoplanets just from their shadows but Kepler has a problem it can't tell if the shadow is made by a giant gassy planet hostile to life or a potentially habitable earth-like planet what we're measuring when a when a planet passes in front of its host star is what is the area of the planet relative to the area of the star that it's passing in front of it's a it's a ratio basically but Jupiter sized planets crossing giant stars full Kepler because they block the same fraction of light as earth sized planets crossing smaller stars to prove a planet is earth sized you first need to measure the size of its star using the world's biggest telescopes but that's time-consuming expensive and it creates a huge exoplanet backlog but astronomer Kavon Stassen has come up with an ingenious shortcut by turning the raw Kepler data into sound what the Kepler telescope directly measures and the data that we use is small changes in brightness that a star produces due to the flickering arising from the boiling and roiling motions of gas at its surface what we can do then is take that light flickering data and transform it in a sound studio for example into audio frequencies and so then we can represent with sound what we're actually detecting with light the bigger the star the more its surface boils with activity making big stars flicker more powerfully converted to sound this boiling becomes a deafening hiss well let's listen to some stars okay can we hear the red giant star please I'm gonna bring up the volume here this is a very large star very low density and so that large amount of hiss is the result of vigorous boiling and churning at the surface of this large red giant star can we get the dwarf star please on smaller stars sunspots dominate the sound profile creating a low-frequency drone actually sounds like a series of clicks come but below the clicks lies the faint hiss Kavon needs to size the star underneath it at a very low level is a little bit of hiss that little bit of is actually the light flickering that we're interested in by accurately measuring the level of this background hiss Kavon can work out the size of the star in this case it's around the same size as our star the Sun cave-ins work could be the breakthrough exoplanet hunters have been hoping for it's cheap the results are practically instantaneous and once you know the size of the star figuring out the size of the planets casting shadows over it is child's play it feels like a very privileged time to be a scientist to be an astronomer working in this area and contributing to the hunt for the next earth here we are actually discovering these worlds by the hundreds and now on the cusp of being able to identify the next earth astronomers suspect there could be tens of billions of rocky earth-like planets in the Milky Way places where perhaps life has gotten a foothold but life as we know it requires water how can scientists possibly find this miracle substance on planets light-years away water divides our living world those with it prosper those about suffer remarkably the water we drink today contains the same atoms as the water dinosaurs drank 100 million years ago it's the same water that formed clouds of the earlier four billion years ago and every organism that has ever existed on earth has used this single ration of water as the biochemical powerhouse that keeps it alive on earth all life requires liquid water to grow and reproduce it's the common ecological requirement for life liquid water is just so good for getting evolution going molecules can dissolve in the water actually interact with each other for more complex chains it does it with charge there's positive charges and negative charges separated between the hydrogen and the oxygen in h2o those charges break apart the hydrocarbons the carbon-based molecules that persist everywhere in nature now that's very rare hardly any other liquids do that so liquid water is a natural starting place when you look out into the universe and say what planets could possibly have life to understand how much liquid water is out there astronomers must first calculate how common water is in all its forms amazingly they find it everywhere they look water is incredibly common in its gaseous form we see water vapor filling the space between the stars we see it in clouds of material that are actually forming new stars and planets right now since water is a fundamental building block of stars and planets exoplanet worlds must surely have it in abundance but if you're looking for life you need to find liquid water and plenty up to find it astronomers take their cue from a fairy tale everybody knows the famous story of Goldilocks and the three bears and the the cup of para girar one was too hot one was too cold I was just right when it comes to cooking up life like a porridge you need to have an environment that's not too hot not too cold just right and traditionally we look for that at a certain distance around a star at first astronomers based this magical distance known as the Goldilocks zone on the Earth's orbit around the Sun but as they found more and more exoplanets they've had to re-evaluate the boundaries for liquid water there isn't a single distance it depends on the brightness of your parent star a dim star you need to be closer a hot star very bright need to be farther away scientists have calculated just how many rocky planets may lie within the Goldilocks zone of their stars it comes out to over 30 billion potentially watering worries even more remarkably recent discoveries have shown us it's not just planets that can bask in the warmth of the Goldilocks zone there may be moons paint blue with oceans - most of the planets were finding our big jupiter-sized planet however a lot of them were are orbiting roughly where the earth is orbiting the Sun so even if the planet that we're finding can't support life it could have a moon a moon with an atmosphere that could support life and the biggest of these rocky moons may resemble our home there could be billions upon billions of XA means out there and even perhaps countless paradises teeming with life David kipping searches for exomoons by looking for double dips in the brightness of distant stars we look for XA means in a very similar way to the way that we look for planets by looking for them transit the host star now if that planet had a moon then we should expect to have one big dip due to the planet and then one smaller depth either to the left or to the right due to the new habitable exomoons may play host to one of the most spectacular sights in the universe imagine a warm rocky world just like our own with oceans mountains but in the sky a massive ringed planet with a fiery sister moon shooting hot magma into space exoplanets and now the vast potential of exomoons int a galaxy filled with the possibilities for life but a rocky surface and liquid oceans may not be enough biology needs the breath of life air backlit by the Sun a halo appears around the earth a pale blue ring of light our atmosphere and we owe it everything the Earth's atmosphere provides the gases that fuel the biochemistry of advanced life but it also protects the oceans from the full fury of the sun's rays preventing the water from boiling away into space without an atmosphere there would be no wind no rain no fresh water and probably no life atmospheres are absolutely essential for life take a look at the planet Earth and you realize that just like the skin of the Apple the skin of the apple preserves the Apple well the atmosphere of our planet preserves the oceans and makes possible the presence of life as we know it scientists in search of living exoplanets hope to detect the thin gassy envelope that should surround these alien worlds to do it they're turning to the power of rainbows in the same way that water splits sunlight into a rainbow astronomers use instruments to split starlight into a band of colors called a spectrum it's one of the oldest tricks and science and one of the most revealing several hundred years ago scientists first began to take something like a prism and put it in front of their telescope so he started taking the light from stars like the Sun and actually spreading it out into a spectrum and what they saw was kind of surprising so instead of seeing a rain continuous rainbow of light they saw that rainbow but they saw these dark lines superimposed on top each chemical elements of the star's atmosphere absorbs different parts of the spectrum creating signature dark bands for instance up the top there's a pair of lines in the yellow part of the spectrum which are due to sodium like a DNA profile for stars spectral analysis has taught us almost everything we know about stars today but these same lines may hide a marvelous secret the faint signal of alien atmospheres and perhaps also alien life so the challenge is that these planets are very small and very faint so we can't actually go and directly measure the light emitted from the planet the same way that you go and measure this lovely spectrum for the Sun instead we have to rely on more indirect methods so one indirect way of doing that is to wait until the planet passes in front of the star when the light of a star passes through an EXO atmosphere the gases that surround the planet should stamp their own faint lines on the star's spectrum so as we watch the light from the stars transmitted through that atmosphere its atmosphere is going to act like a little filter so a part of the star light is going to pass through that atmosphere and we're gonna see that in printing extra lines on it which are due to the planet's atmosphere so that change in the spectrum tells us something about the properties of the planet's atmosphere the one chemical astronomers most want to find is oxygen because only life can produce enough oxygen to be easily detected it's a so-called bio signature the race is now on to find bio signatures in the atmospheres of rocky exoplanets and while some groups look for rainbows indirectly others are tackling the challenge head-on 29 all right we're off then Oppenheimer is part of a team trying to take direct photographs of exoplanets using massive ground-based telescopes we're within minutes of taking our first long exposure and I hope it's good the greatest challenge to imaging exoplanets is the blinding light of the parent star which shines tens of millions of times brighter than the planet itself the trick is to stop the light of the star from entering the telescope sensors by blocking it using a series of masks and lenses called a coronagraph right now we're standing right underneath the telescope's primary mirror and the light comes through a hole in the middle of the mirror and goes into this crazy box here which is full of optics motors sensors and electronics that all allow us to precisely control the star light that's coming through the system using state-of-the-art software they manipulate the coronagraph to black out the unwanted light under good conditions we can actually carve dark holes into this image of the star so that we can see really faint things in those regions coronagraphs present an intriguing problem though errors within the optics produce tiny flares of starlight called speckles that look just like exoplanets but man has come up with an ingenious way to tell speckles from planets so we've developed a technique where we exploit an aspect of speckles which is that they change position in the image depending on what color you take your image at so Ben takes the same image of the star through different color filters and runs them like a movie the speckles appear to move across the screen but the planets stay stuck still allowing Ben to easily pick them out and so I'd like to point out that there is a little thing right here that if you watch for you're careful you'll notice that it doesn't move and the speckles are washing over it this stationary blob is a candidate exoplanet and below it and to the left is a second they both appear to orbit a star around 200 light-years from the earth just a decade ago capturing an image like this through a telescope was unthinkable but today thanks to the ingenuity of astronomers like Ben we have hundreds and by analyzing the light for these distant worlds scientists can work out their chemical composition and potentially the fingerprints of life at this point we're studying much larger planets gaseous things like Jupiter that most likely don't have any kind of life like we know it but that's a first step and we're going to fainter and smaller and smaller planets as time goes on as we develop this technology in the not-too-distant future scientists may be able to simply scan a star for earth-like planets and find the signature of life there we can look right at the light from a little planet around its distant star and that opens up a whole range of possibilities for us to not just detect the planet but to starting the planet I mean this all sounds like science fiction but there is a reality to this we have a scientific method to actually determine whether there is life on another planet life is one thing intelligent life another all together that requires billions of years and a powerful force field like the one we owe our lives to every day if an alien astronomer were to file a report on our home solar system they might make a surprising observation because of all the eight planets that orbit the Sun they could easily conclude the two not one were suitable for life it's an easy mistake to make because the Sun has two planets within its Goldilocks zone the Earth and Mars both planets have surfaces warm enough for liquid water to pool on but while the earth is blessed with warm liquid oceans Mars is dry and dead the one crucial difference between these two planets could be the key to finding truly habitable exoplanets a magnetic shield our Sun is constantly hurling deadly radiation out towards us only our magnetic shield the magnetosphere saves us without it the solar wind would blow our atmosphere away and without an atmosphere liquid water could not exist on the surface in order to have liquid water not only do you need the right temperature but you need the right pressure you know if there were no atmosphere here right now even at the same temperature we are today all of the water would boil off into vapor immediately so where does the Earth's magnetosphere come from and why does it Mars have one actually in the past both Earth and Mars had magnetospheres but Mars lost its around 4 billion years ago and with it the potential for life both the earth and Mars were born into a realm of violence asteroids smashed into their surfaces turning rock and metal into a molten mass as they started to cool a solid crust formed on surface but the molten metal below churned as the planets turn inducing a magnetic field which rose high up above the surface of both planets at the same time active volcanoes pumped gas into the space around each planet protected by the newly formed magnetic field these gases built up into thick atmospheres creating the air pressure for liquid water to run on the surface for over a hundred million years both Mars and Earth for warm wet paradises primed for life to take off then quite suddenly Mars's magnetic protection disappeared the solar wind blew its atmosphere into space and its oceans boiled away leaving the dry sterile red rock we see today Mars is fundamental problem is is that it's smaller than Earth and because it's smaller the internal core of Mars cooled down and solidified and once it becomes a solid metal there's no more magnetic field magnetic field shuts off essentially and the atmosphere therefore is vulnerable to both energy and radiation from the Sun and the rest of the galaxy and probably just blew off whatever life was on there at least on the surface is now completely exposed all rocky planets will one day lose their magnetospheres as their cores cool and turn solid so to know if an exoplanet is alive you need to work out if its magnetosphere is still active but magnetospheres are tough to measure because they are unbelievably weak the earth has a magnetic field of approximately half a Gauss which when you think about it is actually really weak our fridge magnets are about a hundred Gauss they're much stronger Excel planets are too far away for us to measure such weak magnetic fields directly but there is an indirect method when electrons in the solar wind interacts with a planet's magnetosphere they emit radio waves that beam out into space turning the planet into a giant radio beacon astronomers like of geniu hoped to use these signals to spot habitable exoplanets not only that the frequency of the signal should also tell her how big the planet is if we're looking for the magnetic signature in the radio waves of a giant planet say a hot Jupiter we expected to have a strong magnetic field and therefore would have a high frequency and around 100 megahertz kind of where the limit of this radio is however a weaker field like Earth's requires us to go down to lower and lower frequencies so instead of a hundred megahertz we go down to ten megahertz but hunting for exoplanets at ten megahertz presents a unique challenge because the Earth's own magnetic sphere creates a deafening radio roar at that frequency so define alien Earth's using radio requires a dish in space when we want to look for magneto spheres of extrasolar planets we really need to get outside of the earth-moon system in order to get away from all the radio frequencies that are bouncing around the earth with a slew of new technologies and upcoming technologies scientists are edging ever closer to the ultimate prize finding a second earth I wouldn't be surprised if we have that data about an earth and about life on it around another star in 10 or 15 years I'm hoping to see that soon using shadows rainbows and now radio we finally have the tools to detect a planet just like our own but in the rush to find the Earth's identical twin are we missing something big what if earth is an outlier a freakishly lucky place on the very fringes of habitability could there be another kind of planet out there even better for life for years astronomers have scanned the heavens for planets that could sustain life they faced their search on the earth seeking the exact same conditions an exact same size I think right now there is a huge focus to finding earth-like planets now whether or not there actually is life there that is another question altogether but after 20 years of searching for an earth clone the exoplanet hunters may be about to switch targets recent observations have revealed a brand new class of planet it's one that may eclipse our own home we've learned something in the last few years that really shocked us with the Kepler space porn telescope we have found hordes of planets that are a little bigger than the earth we never imagined that there would be such planets in fact in our own solar system there are no planets between the size of the earth and the next largest planet that of Uranus and Neptune astronomers call these mysterious planets super Earths super earths are about three to five times the mass of the earth and there's nothing like that here we don't know what they're like it's an entirely alien sort of planet in just the last few years astronomers have begun to imagine the conditions on this new class of planet and they've come to a startling conclusion super earths could be super habitable there are probably planets out there that are even more hospitable for life planets that have even more chemicals necessary to create the organic materials that create life conditions that make it more likely to get life off the ground imagine a rocky planet twice the size of the earth dramatic volcanism on the surface betrays a vast heart of fire that beats within its core we expect that a heavier earth will be more geologically active that the increased amount of geothermal heat within the super earth will lead to stronger motions of the magma underneath the crust belching volcanoes dot the surface of this super earth their gases feed a super thick atmosphere and help to regulate a super stable climate many times life on Earth was nearly extinguished for example once upon a time the earth was snowball earth completely covered in ice maybe in these other planets there are earth in which snowball earth never happened that the taught climate was always stable and temperate the grip of gravity is three times stronger here than we're used to it pulls mountain ranges down to a third the height they'd be on earth gravity also flattens the ocean bed making shallower CDs filled with volcanic island chains and the nutrient-rich waters that surround these archipelagos provide the perfect conditions for life in these other planets perhaps they have conditions which would make DNA get off the ground much earlier and flourish much more quickly finally our super earth may be protected by a super magnetosphere the magnetic field strength is a condition both of the mass of the planet as well as its rotation speed and so it is quite likely that a planet that is a couple of times bigger than the earths would be able to develop a stronger magnetic field may shield the planet even better than our magnetic field shields us having a stronger magnetosphere would be a distinct advantage for life on a super earth surrounding the Milky Way's most plentiful kind of star the M dwarf or red dwarf star red dwarf habitable zones are much closer in than the earth is to the Sun because their host star is so dim as if you took the terrestrial planets in our own solar system and zapped it with a shrink ray gun and shrunk them down to orbital periods that are less than about 30 days meaning that they're very close to their stars some astronomers believe these planets are at risk from solar activity such as deadly flares but a super-earth with a super protective magnetosphere may well resist these deadly rays allowing life to flourish under a psychedelic sky full of swirling Aurora's if one was standing on a super earth we would see the aurora come down to lower latitudes might get different colors if I had the opportunity to travel to one of these exoplanets I would snap that up pretty quickly most intriguing of all if life does exist on a red dwarf super earth it could be home to the longest-lived civilizations in the entire universe the advantage of the M Dwarfs is that they last for much longer and if you had a super earth then keeping a strong magnetic field going for billions and billions of years especially now around a red dwarf that is going to exist for billions and billions of years you might be in that perfect system where life can exist and evolve into even more complex beings than us we're getting so close our local neighborhood of stars teens with red dwarfs bursting with the potential for advanced life but they're also cosmic killers out there lurking in our galaxy prime to wipe out life on a regular basis is anywhere safe the exoplanet revolution is in full swing the Kepler space telescope has scanned our local neighborhood of stars for planets and it's found them by the thousands for a long time we didn't know if the other stars in our galaxy had planets and for thousands of years there was no way to answer that question finally now with modern technology we can do that and to our surprise we found they are extremely common from Kepler's small sample astronomers believe there could be tens of billions of rocky earth-like planets throughout the Milky Way where life may already be thriving but how many of these countless worlds is held onto this life long enough for intelligence to evolve the answer surprisingly may depend on a planet's galactic zip code the universe is not a happy safe place the universe wants to kill us it's incredibly violent out there they're solar flares and supernovae and black holes and colliding galaxies and all these really amazingly dangerous and violent events it's actually kind of amazing that we're here at all in order to develop advanced intelligent life an exoplanet may have to avoid these cosmic killers for over three billion years if we look at the history of the earth the first thing that happens that's important is the origin of life right away very quickly but then nothing for a long time you have nothing but microbes stomping on the earth for the first two and a half billion years the earth was ruled by single-celled Goom multicellular life has only been around for a billion years fish for 500 million mammals for 200 million and modern humans have only walked the earth for the last 200,000 years the lesson is clear it takes a long time to cook up intelligent life but most planets in the Milky Way don't have that kind of time astronomers believe that a planet's position within a galaxy may determine if it gets hit by global extinction events there's an idea of a habitable zone for a galaxy and it's an analogy to the habitable zone around stars stars too close to the galactic center are in the firing line from their violent neighbors which frequently blast them with deadly high-energy radiation in the middle of a galaxy we have a lot of bright stars and young stars and maybe even supernova going off and so there's a very harsh radiation field that's not good for life fired up by the supermassive black hole that sits at the center of the Milky Way this cosmic Killzone stretches out around 8,000 light years from the galactic center and extends out along the densely packed spiral arms any planets that exist within this zone are likely to have their surfaces regularly scrubbed clean of life fortunately for us our home star the Sun sits in a relatively empty quiet zone between two of the galaxy's spiral arms so there's this idea that there's a band in the middle of the galaxy that's the Galactic habitable zone where you don't have too many stars going off you don't have too many supernovae so it's quiet in that way those might be great places for complex life these green zones are like the suburbs the Milky Way galaxy they're sheltered from the worst of the galaxy's radiation it's here that earth-like worlds will have the luxury of long uninterrupted periods for life to take hold and develop into more complex forms and eventually perhaps intelligent life like us the Galactic habitable zone is no more than a fledgling theory but if it's true it reduces the number of places where advanced life could flourish in the Milky Way the good news is those places should be near us and aliens more likely to be on our doorstep and with our technology getting better every day it surely won't be long before we find them I think in 20 years time I'm gonna be able to look up into the night sky and say there really is another place I could stand like this and feel at home suddenly we humans will realize for the first time that there are other cultures other civilizations probably other religions out there among the stars and we are just one member of a grand galactic tribe to have cousins that we one day may communicate with seems to me to be potentially one of the greatest developments that humanity will ever ever experience and if that isn't worth doing I don't know what is