0:00:03 > 0:00:06Tonight on The Sky At Night, we're going interstellar.
0:00:06 > 0:00:09Travelling to the stars has always seemed like an impossible dream,
0:00:09 > 0:00:11but now some scientists believe
0:00:11 > 0:00:13that it may be possible within our lifetimes.
0:00:13 > 0:00:16And that prospect has just become even more enticing
0:00:16 > 0:00:18because we have a target to aim for.
0:00:18 > 0:00:21Within the last few weeks, astronomers have announced
0:00:21 > 0:00:25the discovery of a hospitable planet around the Sun's nearest neighbour,
0:00:25 > 0:00:26Proxima Centauri.
0:00:27 > 0:00:29On tonight's programme,
0:00:29 > 0:00:32we'll be finding out how this new planet was detected
0:00:32 > 0:00:34and why it's such an important discovery.
0:00:36 > 0:00:39And Jim Al-Khalili will be exploring the revolutionary new technology
0:00:39 > 0:00:42that might take us deep into space.
0:00:42 > 0:00:44Welcome to The Sky At Night.
0:01:14 > 0:01:19On August 24th, astronomers made an extraordinary announcement.
0:01:19 > 0:01:21Scientists are hailing a major discovery -
0:01:21 > 0:01:24a new planet which they've called Proxima b.
0:01:24 > 0:01:27At just four light years away, it's relatively close to us.
0:01:27 > 0:01:29It's roughly the same size as Earth,
0:01:29 > 0:01:32and because it's just the right distance away from its star,
0:01:32 > 0:01:35it could be the right temperature to have liquid water
0:01:35 > 0:01:37and possibly life.
0:01:38 > 0:01:40Over the last few years,
0:01:40 > 0:01:45we have identified over 3,000 planets orbiting other stars,
0:01:45 > 0:01:47but this one is special.
0:01:47 > 0:01:50It's already been called one of the discoveries of the century.
0:01:50 > 0:01:54So what makes this planet such an enticing target
0:01:54 > 0:01:56for our first interstellar mission?
0:01:57 > 0:02:01Proxima b is in orbit around Proxima Centauri,
0:02:01 > 0:02:03the closest star to our sun.
0:02:03 > 0:02:09Only discovered in 1915, Proxima is an apparently unremarkable star.
0:02:09 > 0:02:11It's the smallest of the three stars
0:02:11 > 0:02:13that make up the Alpha Centauri system.
0:02:13 > 0:02:18A red dwarf, like 70% of the stars in the Milky Way,
0:02:18 > 0:02:20it's just 12% of the mass of the sun.
0:02:24 > 0:02:28That small size means the pressure and the temperature at the core
0:02:28 > 0:02:31are much less than in our sun,
0:02:31 > 0:02:34and so the processes of nuclear fusion that power the star
0:02:34 > 0:02:36proceed much more slowly.
0:02:37 > 0:02:40And so, Proxima Centauri is cool.
0:02:40 > 0:02:43Its surface temperature is only half that of the sun
0:02:43 > 0:02:46and its luminosity is 500 times lower.
0:02:46 > 0:02:50In fact, it's so dim that even though it's the closest star to us,
0:02:50 > 0:02:54it can't be seen from Earth with the naked eye.
0:02:54 > 0:02:57But the discovery of a planet around Proxima Centauri
0:02:57 > 0:02:59makes it a much more exciting neighbour.
0:03:02 > 0:03:05This is the paper published in Nature just last month
0:03:05 > 0:03:08that announced the discovery of the planet
0:03:08 > 0:03:10that the team called Proxima b.
0:03:10 > 0:03:13I've come here to Queen Mary University of London
0:03:13 > 0:03:15to meet Guillem Anglada-Escude,
0:03:15 > 0:03:18the leader of the team that made this remarkable discovery.
0:03:20 > 0:03:24Anglada was part of a project called the Pale Red Dot
0:03:24 > 0:03:27that used the European Southern Observatory's telescopes
0:03:27 > 0:03:32in Chile to observe the star for 60 straight nights last spring,
0:03:32 > 0:03:34and it's only now, after careful analysis,
0:03:34 > 0:03:37that the results have been released.
0:03:37 > 0:03:38Congratulations. Thank you.
0:03:38 > 0:03:40It's a wonderful, wonderful discovery,
0:03:40 > 0:03:43but how on Earth do you tell that this tiny planet is there
0:03:43 > 0:03:46going around the star?
0:03:46 > 0:03:49Well, that... Well, that took some time.
0:03:49 > 0:03:51It was not something that happened from one day to the next.
0:03:51 > 0:03:53But I think the thing that's difficult for me
0:03:53 > 0:03:56to get my head round is I sort of imagine you taking a picture
0:03:56 > 0:03:59and looking for the planet in the image, but that's not how it works.
0:03:59 > 0:04:00No. No, not in these cases.
0:04:00 > 0:04:02And most of the planets don't work this way because
0:04:02 > 0:04:05the planets are very faint compared to the stars.
0:04:05 > 0:04:07So what you see is the star,
0:04:07 > 0:04:09and we are using a method that is indirect.
0:04:09 > 0:04:11So we see what the planet is doing to the star because
0:04:11 > 0:04:13the planet and the star both have mass
0:04:13 > 0:04:15and therefore they attract gravitationally,
0:04:15 > 0:04:19and the planet going around the star moves the star itself,
0:04:19 > 0:04:20and that is what we are trying to measure.
0:04:20 > 0:04:22I was going to say,
0:04:22 > 0:04:25because the planets are small compared to the stars,
0:04:25 > 0:04:27so this motion must be very subtle.
0:04:27 > 0:04:29For example, the Earth can't have much effect on the sun.
0:04:29 > 0:04:31The effect of the Earth on the sun is small -
0:04:31 > 0:04:33it's about 10 centimetres per second.
0:04:33 > 0:04:37So you can think of just moving like this, like an ant.
0:04:37 > 0:04:41For planets around stars that are much smaller, like Proxima,
0:04:41 > 0:04:45the star is smaller, so the planet is making the star move more,
0:04:45 > 0:04:49and in that case, the motion is about metre per second level.
0:04:49 > 0:04:54Wow, so you are able to detect that a whole star is moving
0:04:54 > 0:04:56at a metre per second, which is...
0:04:56 > 0:04:58That's sort of walking pace.
0:04:58 > 0:05:02Exactly. And it's not a trivial thing to do because what you have is
0:05:02 > 0:05:04the planet going around the star periodically,
0:05:04 > 0:05:08and we see this motion going up and down, up and down.
0:05:08 > 0:05:11So you see a wave, like something like this.
0:05:11 > 0:05:13And that's the signature that tells you that there's a planet.
0:05:13 > 0:05:16When you see something like this in a star that repeats over time,
0:05:16 > 0:05:20that is always consistent and a number of other things,
0:05:20 > 0:05:23this is when you're convinced that you have a planet around a star.
0:05:23 > 0:05:25Excellent. And then from there, the next question is,
0:05:25 > 0:05:27what do we know about this planet?
0:05:27 > 0:05:29What can we tell, other than the fact that it's there
0:05:29 > 0:05:31and it's making the star move?
0:05:31 > 0:05:34So, just from the motion that we detect, this time,
0:05:34 > 0:05:37sorry, this curve, this oscillation, we know the period.
0:05:37 > 0:05:40And for this planet, what is that number?
0:05:40 > 0:05:41It's 11.2 days.
0:05:41 > 0:05:44So it's going round pretty quickly. Yes.
0:05:44 > 0:05:48From that we can infer the distance between the star and the planet.
0:05:48 > 0:05:50Just from knowing how gravity works, basically.
0:05:50 > 0:05:53Yes. This is Kepler's law, the first Kepler's law.
0:05:53 > 0:05:55And so what is that separation for this planet?
0:05:55 > 0:05:58In this case, it is around 5% an astronomical unit.
0:05:58 > 0:06:00OK. So that's what?
0:06:00 > 0:06:04That something like 7.5 million kilometres, something like that?
0:06:04 > 0:06:06You're faster than me. Yeah, OK.
0:06:06 > 0:06:07But it's very close to the star.
0:06:07 > 0:06:10That's much closer to the star than Mercury is to the sun.
0:06:10 > 0:06:14Yes. Yeah. It's about a tenth of the distance
0:06:14 > 0:06:16between Mercury and the sun.
0:06:16 > 0:06:21And the other thing we get from this curve is the mass of the planet.
0:06:21 > 0:06:22And what is that mass?
0:06:22 > 0:06:26This mass is 1.3, 1.4 Earth masses.
0:06:26 > 0:06:30So for this system, we've got a one and a third Earth mass planet
0:06:30 > 0:06:33going around its star every 11 days.
0:06:33 > 0:06:34So, just thinking about that,
0:06:34 > 0:06:37I expect... That's much closer to the star than Mercury is to the sun,
0:06:37 > 0:06:39so I'd expect that to be hot.
0:06:39 > 0:06:42Yes, you would expect that to be hot if that was the sun,
0:06:42 > 0:06:46but this is Proxima and it's a red star, it's a red dwarf.
0:06:46 > 0:06:48And it's a small red dwarf,
0:06:48 > 0:06:52so Proxima has around 12% of the mass of the sun,
0:06:52 > 0:06:54so this means that if you want to keep warm,
0:06:54 > 0:06:56you have to be much closer to the star.
0:06:56 > 0:06:59Right. And this is when the magic happens,
0:06:59 > 0:07:01where you put all the numbers together and you can estimate
0:07:01 > 0:07:04how much light, how much energy is reaching the planet.
0:07:04 > 0:07:06And this amount of energy is about 70%,
0:07:06 > 0:07:10the amount of energy that Earth is receiving from the sun.
0:07:10 > 0:07:13And so it's actually pretty warm by planetary standards.
0:07:13 > 0:07:15By planetary standards.
0:07:15 > 0:07:17The next calculation you can do is try to estimate
0:07:17 > 0:07:19the temperature that this planet would have.
0:07:19 > 0:07:22And you do the numbers and you get 240 Kelvins.
0:07:22 > 0:07:24That's what? -30 centigrade.
0:07:24 > 0:07:27-30, -40 Celsius, something like this.
0:07:27 > 0:07:29But you would say, oh, that would be frozen,
0:07:29 > 0:07:31but the same would happen to Earth.
0:07:31 > 0:07:34Earth is about 255 Kelvins,
0:07:34 > 0:07:38which means it's -20 Celsius. And this is not -20, right?
0:07:38 > 0:07:42And what happens there is that Earth has an atmosphere and keeps it warm.
0:07:42 > 0:07:45So in principle, this planet, if it has an atmosphere,
0:07:45 > 0:07:48it would have a greenhouse effect, and that would keep the planet warm.
0:07:48 > 0:07:51So with an atmosphere, it might be warm enough to have liquid water.
0:07:51 > 0:07:52Yes. That's the...
0:07:52 > 0:07:55That's also the highlight of the discovery.
0:07:55 > 0:07:57Well, it's great to be talking about this.
0:07:57 > 0:07:58Congratulations again.
0:07:58 > 0:08:01I can't wait to see what further research comes out
0:08:01 > 0:08:03and what else is there. Thanks a lot. Thank you.
0:08:05 > 0:08:09The discovery of a potential earthlike planet so close to us
0:08:09 > 0:08:12instantly raises another question -
0:08:12 > 0:08:15could we send a spacecraft to visit it?
0:08:17 > 0:08:20Everybody ready to say goodbye to our solar system?
0:08:20 > 0:08:24In science fiction, interstellar travel always seems easy.
0:08:24 > 0:08:26Here we go.
0:08:26 > 0:08:28In the film Interstellar,
0:08:28 > 0:08:31it's simply a matter of dropping through a wormhole.
0:08:33 > 0:08:35Maximum warp. Punch it.
0:08:35 > 0:08:39In Star Trek, a warp drive is used to bend the shape of space-time.
0:08:43 > 0:08:44Compressor.
0:08:47 > 0:08:51And in the Star Wars universe, you just need to throw a switch
0:08:51 > 0:08:54to accelerate past light speed and into hyperspace.
0:08:58 > 0:09:00But in reality, travelling to the stars
0:09:00 > 0:09:03has always seemed an impossible dream.
0:09:03 > 0:09:04Until now.
0:09:05 > 0:09:09We asked Jim Al-Khalili to explain why it's so difficult
0:09:09 > 0:09:13to travel to the stars and to investigate the technology
0:09:13 > 0:09:16that might be about to make interstellar travel possible.
0:09:18 > 0:09:20For decades, centuries, even,
0:09:20 > 0:09:24we've been wondering what kind of fast engines would be needed
0:09:24 > 0:09:25to carry us to the stars.
0:09:25 > 0:09:29There's one simple overwhelming problem when it comes to
0:09:29 > 0:09:32travelling across interstellar space.
0:09:32 > 0:09:36As Douglas Adams once said, "Space is big. Really big."
0:09:38 > 0:09:42And so far we've only been able to explore the tiniest fraction of it.
0:09:44 > 0:09:48The craft that we've sent furthest into space is Voyager 1.
0:09:48 > 0:09:50Launched in 1977,
0:09:50 > 0:09:54it visited Jupiter and Saturn before heading for the outer edges
0:09:54 > 0:09:58of the solar system. Now, nearly 40 years later,
0:09:58 > 0:10:01it's escaped the solar system and has started the journey
0:10:01 > 0:10:03through interstellar space.
0:10:03 > 0:10:05But it has a very, very long way to go
0:10:05 > 0:10:07to get as far as Proxima Centauri.
0:10:09 > 0:10:12Any practical mission to the stars would need to get there
0:10:12 > 0:10:15in a reasonable amount of time - say 20 years.
0:10:15 > 0:10:18But that means going incredibly fast.
0:10:19 > 0:10:23The distance between Earth and Proxima Centauri
0:10:23 > 0:10:27is just under 4.25 light years.
0:10:27 > 0:10:31Now, that works out at roughly 40 trillion kilometres,
0:10:31 > 0:10:35or 4 x 10 to the 13.
0:10:35 > 0:10:39Now, in order to cover this vast distance in 20 years,
0:10:39 > 0:10:43a spacecraft would have to travel at 20% the speed of light.
0:10:43 > 0:10:49That's roughly 64,000 kilometres per second.
0:10:51 > 0:10:54If you compare this with the speed that Voyager currently travels at -
0:10:54 > 0:10:58a mere 17km per second.
0:10:58 > 0:11:02It is this disparity between the speed that is required
0:11:02 > 0:11:06and what is commonly achievable that has always made interstellar travel
0:11:06 > 0:11:08seem almost impossible.
0:11:11 > 0:11:13The biggest problem in reaching the speeds needed
0:11:13 > 0:11:17for interstellar travel is the sheer amount of energy required
0:11:17 > 0:11:19to produce the acceleration.
0:11:19 > 0:11:24The Saturn V was the largest and most powerful rocket ever built.
0:11:24 > 0:11:29It weighed nearly 3,000 tonnes and almost all of that was the fuel
0:11:29 > 0:11:34required to propel its meagre 44-tonne payload to the moon.
0:11:34 > 0:11:37Accelerating a spacecraft to the speeds needed to reach the stars
0:11:37 > 0:11:41would require much more energy than you could ever produce
0:11:41 > 0:11:42with a conventional rocket.
0:11:42 > 0:11:46It would need a completely new type of propulsion system.
0:11:48 > 0:11:51In the 1970s, the British Interplanetary Society
0:11:51 > 0:11:54set out to see if it was possible to design a spacecraft
0:11:54 > 0:11:57that could travel at 12% the speed of light.
0:11:57 > 0:12:01Such a craft would reach Proxima Centauri in about 40 years.
0:12:01 > 0:12:04They called it Project Daedalus.
0:12:04 > 0:12:05And here it is.
0:12:05 > 0:12:09It was to be huge craft - 200 metres along -
0:12:09 > 0:12:12and to save on the energy of getting it off the Earth's surface,
0:12:12 > 0:12:14it was to be built in orbit.
0:12:14 > 0:12:18Now, it would be powered by a nuclear pulse engine
0:12:18 > 0:12:22using nuclear fusion, a technology that hasn't even been invented yet,
0:12:22 > 0:12:25but that was seen to provide much more energy than chemical rockets
0:12:25 > 0:12:28that we use today. Still, to get it up to speed,
0:12:28 > 0:12:33it would need 50,000 tonnes of deuterium helium-3 fuel
0:12:33 > 0:12:36that would be stored in these vast tanks.
0:12:36 > 0:12:39Now, there's not enough helium on Earth for this,
0:12:39 > 0:12:43so they suggested that helium could be harvested
0:12:43 > 0:12:45from the surface of Jupiter.
0:12:45 > 0:12:46Easy, really.
0:12:47 > 0:12:48Perhaps, unsurprisingly,
0:12:48 > 0:12:51Project Daedalus never made it off the drawing board.
0:12:54 > 0:12:58But, more than 40 years later, there's another suggestion.
0:12:58 > 0:13:02In April, Stephen Hawking and Internet billionaire Yuri Milner
0:13:02 > 0:13:06announced that they were putting up $100 million to develop
0:13:06 > 0:13:10a new interstellar project called Breakthrough Starshot.
0:13:10 > 0:13:13For the first time in human history,
0:13:13 > 0:13:16we can do more than just gaze at the stars.
0:13:16 > 0:13:18We can actually reach them.
0:13:20 > 0:13:22There are two key features to this new system.
0:13:22 > 0:13:26The first is that the spacecraft won't be carrying its own engines.
0:13:26 > 0:13:31Instead, it will have a sail that is propelled by the force of light.
0:13:32 > 0:13:34Released from a launcher in orbit,
0:13:34 > 0:13:38the spacecraft will be accelerated by the second new concept -
0:13:38 > 0:13:41a vast array of lasers fired from Earth.
0:13:43 > 0:13:46Theoretically, the planned 100 gigawatt laser
0:13:46 > 0:13:50that has about the same power output as 100 nuclear power stations
0:13:50 > 0:13:53could accelerate a spacecraft to nearly a quarter
0:13:53 > 0:13:56of the speed of light in about two minutes.
0:13:58 > 0:14:01It would reach Mars in just half an hour.
0:14:01 > 0:14:04It would overtake Voyager in about four days
0:14:04 > 0:14:08and it would get to Proxima Centauri in little over 20 years.
0:14:10 > 0:14:12There's only one problem -
0:14:12 > 0:14:15to reach those speeds, the spacecraft will have to be
0:14:15 > 0:14:19incredibly light, probably weighing no more than one gram.
0:14:20 > 0:14:22It's not exactly the Starship Enterprise,
0:14:22 > 0:14:26but what could you achieve with a one-gram spacecraft?
0:14:26 > 0:14:29I called up Harvard cosmologist Avi Loeb,
0:14:29 > 0:14:31one of the scientists behind the project, to find out more.
0:14:33 > 0:14:36Avi, this is a hugely ambitious project.
0:14:36 > 0:14:38Do you really think it's possible?
0:14:38 > 0:14:41Yes, we hope that we can achieve the goals
0:14:41 > 0:14:43of this very ambitious project
0:14:43 > 0:14:45within the lifetime of our generation.
0:14:46 > 0:14:51This project is as ambitious as was building the pyramids
0:14:51 > 0:14:56or building cathedrals in ancient times.
0:14:56 > 0:15:00You can think of it as the cathedral of our generation.
0:15:00 > 0:15:04The only difference from past cathedrals is that it reaches
0:15:04 > 0:15:06all the way out the stars.
0:15:06 > 0:15:08And what about the cost?
0:15:08 > 0:15:10Presumably this is going to be hugely expensive.
0:15:12 > 0:15:16The cost is up to $10 billion -
0:15:16 > 0:15:21of the order of the biggest science projects that we encountered so far,
0:15:21 > 0:15:26such as Cern or the James Webb Space Telescope.
0:15:26 > 0:15:31A critic will say that's a lot of money to send a one-gram spacecraft
0:15:31 > 0:15:36through space. How much science can you do with a one-gram payload?
0:15:36 > 0:15:41Fortunately, these days we can pack a lot of smart electronics
0:15:41 > 0:15:45into a single gram. If you look at a cellphone and strip it
0:15:45 > 0:15:49from the protective case
0:15:49 > 0:15:51and strip it from the human interface,
0:15:51 > 0:15:55you're left roughly with a gram, and that includes a camera,
0:15:55 > 0:15:59a communication device, navigation -
0:15:59 > 0:16:03all of the ingredients we need in the Starshot spacecraft.
0:16:03 > 0:16:07And presumably, if the technology is successful,
0:16:07 > 0:16:10it could be used for other than just interstellar travel.
0:16:10 > 0:16:14Yes, this technology can be used to explore the space in between us
0:16:14 > 0:16:16and the nearest star.
0:16:16 > 0:16:21For example, we could search for life within the solar system.
0:16:21 > 0:16:24It would take us only a few days to reach Pluto,
0:16:24 > 0:16:29instead of about a decade that it took New Horizons to get there.
0:16:29 > 0:16:31And so, in principle, the technology that we develop
0:16:31 > 0:16:35will allow us to probe the edge of the solar system
0:16:35 > 0:16:37within a relatively short time.
0:16:37 > 0:16:40And what's the timescale for the project?
0:16:40 > 0:16:41What happens next?
0:16:41 > 0:16:46The first five to ten years will be dedicated to a feasibility study,
0:16:46 > 0:16:51where we will demonstrate the technology of reaching a speed
0:16:51 > 0:16:55far larger than previously reached with chemical rocketry
0:16:55 > 0:16:57in a laboratory set-up.
0:16:57 > 0:17:03And after demonstrating that, we hope to expand the system
0:17:03 > 0:17:05until we reach the final design
0:17:05 > 0:17:09within about 20 to 30 years from now.
0:17:09 > 0:17:12Following that, we hope to launch the spacecrafts,
0:17:12 > 0:17:16and it will take them about 20 years to reach Alpha Centauri,
0:17:16 > 0:17:21and another four years for the signal from them to teach us.
0:17:21 > 0:17:23And so, altogether,
0:17:23 > 0:17:29we hope to get those signals while we are still alive.
0:17:29 > 0:17:31I'm the same age as you,
0:17:31 > 0:17:34so I just hope we're both around to see this project completed
0:17:34 > 0:17:36and successful in our lifetime.
0:17:36 > 0:17:38I wish you the very best of luck.
0:17:38 > 0:17:39Thank you so much.
0:17:43 > 0:17:45Before the system becomes a reality,
0:17:45 > 0:17:47there are many other technical problems to solve...
0:17:49 > 0:17:53..like building a material that can withstand a 100 gigawatt laser
0:17:53 > 0:17:56without burning up,
0:17:56 > 0:17:59and how to get a signal back from a tiny spacecraft
0:17:59 > 0:18:03hurtling away from us at 20% the speed of light.
0:18:04 > 0:18:06It's an exciting prospect.
0:18:06 > 0:18:09There are still many practical problems to solve and, you know,
0:18:09 > 0:18:12it's still hard to believe that it would succeed.
0:18:12 > 0:18:16But looking at this project makes me realise that something I always
0:18:16 > 0:18:21thought was unreachable may actually be possible.
0:18:21 > 0:18:24If it succeeds, it wouldn't just revolutionise space travel,
0:18:24 > 0:18:28it would vastly increase our knowledge of the universe around us.
0:18:28 > 0:18:31And who knows? With the will and the money,
0:18:31 > 0:18:33it may actually happen in my lifetime.
0:18:37 > 0:18:40If we do develop the means to travel to the stars,
0:18:40 > 0:18:43Proxima Centauri won't be our only destination.
0:18:43 > 0:18:46There are other nearby stars we could visit.
0:18:47 > 0:18:51Pete has been identifying some of the other potential targets.
0:18:54 > 0:18:59Within 15 light years of the sun, there are approximately 58 stars
0:18:59 > 0:19:03in 39 separate stellar systems, each being very different.
0:19:04 > 0:19:07This group of stars are the closest to being within reach
0:19:07 > 0:19:09of an interstellar mission.
0:19:09 > 0:19:12Many of them are cool red dwarfs like Proxima Centauri,
0:19:12 > 0:19:16and the more optimistic studies place at least one planet
0:19:16 > 0:19:19in the habitable zone around each one.
0:19:19 > 0:19:22One of the closest red dwarfs is Barnard's Star.
0:19:22 > 0:19:24Just six light years away,
0:19:24 > 0:19:27it has the highest proper motion of any star in the sky.
0:19:27 > 0:19:32At present, it's well placed in the west-southwest at around 9pm,
0:19:32 > 0:19:36positioned off the eastern shoulder of Ophiuchus.
0:19:36 > 0:19:42To find it, look for a faint V in the sky known as Poniatovski's Bull.
0:19:42 > 0:19:44Barnard's Star sits to the top right.
0:19:44 > 0:19:48The closest sunlike star to ours is Tau Ceti.
0:19:48 > 0:19:5311.9 light years away, it sits low in the constellation of Cetus,
0:19:53 > 0:19:55rising in the east-southeast,
0:19:55 > 0:19:58and is one of my favourite stars to observe.
0:19:58 > 0:20:01It's at its highest from 3am.
0:20:01 > 0:20:03Locate the Great Square of Pegasus,
0:20:03 > 0:20:06then follow the left-hand side down
0:20:06 > 0:20:09to a bright star known as Deneb Kaitos.
0:20:09 > 0:20:12Off to the left is a quadrilateral of fainter stars,
0:20:12 > 0:20:15Tau being the southernmost of these four.
0:20:16 > 0:20:19With a possible system of five planets in orbit,
0:20:19 > 0:20:21including one in the habitable zone,
0:20:21 > 0:20:25Tau Ceti would make an exciting target for an interstellar mission.
0:20:26 > 0:20:29There are likely to be unique and bizarre planets in orbit
0:20:29 > 0:20:32around almost all of the stars in the sky.
0:20:35 > 0:20:39And if we could send a tiny probe to just one of these stars,
0:20:39 > 0:20:42imagine how amazing it would be to be able to look at
0:20:42 > 0:20:44another solar system at close quarters.
0:20:48 > 0:20:51Proxima b is undoubtedly an exciting discovery,
0:20:51 > 0:20:54but just because it could have liquid water on the surface
0:20:54 > 0:20:57doesn't mean it's going to turn out like Earth.
0:20:57 > 0:21:00And it certainly doesn't mean that it will be habitable,
0:21:00 > 0:21:03because planets in very similar environments
0:21:03 > 0:21:05can develop in very different ways.
0:21:07 > 0:21:10Just look at Earth and Venus -
0:21:10 > 0:21:12twin planets of about the same size
0:21:12 > 0:21:15and at a similar distance from the sun.
0:21:15 > 0:21:18But they've developed very differently.
0:21:18 > 0:21:23Where the Earth became a warm and temperate world, a haven for life,
0:21:23 > 0:21:27Venus lost its water and succumbed to a runaway greenhouse effect.
0:21:29 > 0:21:32Its sulphurous atmosphere heated its surface
0:21:32 > 0:21:36to more than 450 degrees centigrade.
0:21:36 > 0:21:39It is completely unsuitable for life.
0:21:40 > 0:21:42Proxima b might be like Earth,
0:21:42 > 0:21:45but it could equally well be like Venus,
0:21:45 > 0:21:47or like something else entirely.
0:21:47 > 0:21:50And so, what can we say about conditions on the planet
0:21:50 > 0:21:53and about its chances of being hospitable to life?
0:21:54 > 0:21:59Maggie has been talking to expert on planetary atmospheres Jo Barstow.
0:21:59 > 0:22:00Yes.
0:22:03 > 0:22:06So, Joanna, can you tell me how excited you are about
0:22:06 > 0:22:08the discovery of this new exoplanet?
0:22:08 > 0:22:10Well, incredibly excited.
0:22:10 > 0:22:14I think this is pretty much going to transform the field that I work in.
0:22:14 > 0:22:17How is it similar to Earth, or how is it different?
0:22:17 > 0:22:20Well, one of the things we think is the same based on the mass
0:22:20 > 0:22:22that's been measured with these new results
0:22:22 > 0:22:25is that it's likely to be rocky, and that's a good sign.
0:22:25 > 0:22:27That means that it should have a solid surface,
0:22:27 > 0:22:29that means that there should be potential, maybe,
0:22:29 > 0:22:32for something to live on that surface.
0:22:32 > 0:22:35The major difference is driven by the fact that it's orbiting
0:22:35 > 0:22:37much closer to that star,
0:22:37 > 0:22:42and that introduces all sorts of potential problems.
0:22:42 > 0:22:44And one of those is that we think the planet
0:22:44 > 0:22:47is something we call tidally locked.
0:22:47 > 0:22:50And I have here a very small star.
0:22:50 > 0:22:52Oh, yes.
0:22:52 > 0:22:55And a very large planet. And a very large, not to scale, planet at all.
0:22:56 > 0:22:59So what's happening, because the planet is so close to the star,
0:22:59 > 0:23:03tidal forces mean that the same side of the planet
0:23:03 > 0:23:05is always facing the star.
0:23:05 > 0:23:08So as it goes round the star, it's rotating like this.
0:23:08 > 0:23:12Its day is actually the same length as its year.
0:23:12 > 0:23:15So that's like the moon? Exactly like the moon.
0:23:15 > 0:23:18From Earth we can only see one side of the moon because that's the side
0:23:18 > 0:23:19that always faces the Earth.
0:23:19 > 0:23:22And so what that means is that one side is getting all of the light
0:23:22 > 0:23:25from the star and therefore getting much hotter
0:23:25 > 0:23:27than the other side of the planet.
0:23:27 > 0:23:29And that could potentially produce
0:23:29 > 0:23:31very extreme temperature differences.
0:23:31 > 0:23:33So, looking at life, how does that impact?
0:23:33 > 0:23:36Is there any way of evening out that temperature or do you always have
0:23:36 > 0:23:38that sort of dichotomy - the hot side and the cold side?
0:23:38 > 0:23:42Well, thankfully, if the planet has an atmosphere, then it might help
0:23:42 > 0:23:44to even out that temperature difference.
0:23:44 > 0:23:46The atmosphere actually sort of lets the heat be distributed
0:23:46 > 0:23:48around the planet? Yes.
0:23:48 > 0:23:51Basically, it enables the heat to be distributed from
0:23:51 > 0:23:54what we call the day side, the side that's receiving all the light,
0:23:54 > 0:23:57round to the night side, and it evens everything out.
0:23:57 > 0:23:59What is the likelihood of having an atmosphere?
0:23:59 > 0:24:01I mean, because it's closer to that star.
0:24:01 > 0:24:03Yes, and that is also a bit of a problem.
0:24:03 > 0:24:06I mean, we want it to have an atmosphere quite apart from the fact
0:24:06 > 0:24:10that it can even out temperature differences to give any life there
0:24:10 > 0:24:13something to breathe. And if you were going to have an ocean
0:24:13 > 0:24:16or liquid water, then you also need to have an atmosphere.
0:24:16 > 0:24:21But because it's so close to the star, it's possible it may no longer
0:24:21 > 0:24:23have an atmosphere, even if it did once.
0:24:23 > 0:24:26So this star doesn't give out as much light as the sun,
0:24:26 > 0:24:30but what it does do is it gives out about the same amount of X-rays
0:24:30 > 0:24:33as the sun does. And for us out at Earth,
0:24:33 > 0:24:35the sun's X-rays are not an enormous problem,
0:24:35 > 0:24:38but if you imagine being 20 times closer,
0:24:38 > 0:24:41then suddenly those X-rays do become a bit of a problem.
0:24:41 > 0:24:44X-rays are not great for life.
0:24:45 > 0:24:49Also, when this star experiences what we call coronal mass ejections,
0:24:49 > 0:24:53which are events where some of the material actually leaves the star
0:24:53 > 0:24:54and goes out into space,
0:24:54 > 0:24:57that causes on Earth beautiful auroral displays,
0:24:57 > 0:24:59but for a planet like Proxima Cen b...
0:24:59 > 0:25:03That much closer. ..then you're going to have problems, potentially,
0:25:03 > 0:25:05because those coronal mass ejections could actually start
0:25:05 > 0:25:08to eat away at the atmosphere of that planet.
0:25:08 > 0:25:10And if it experiences enough of those,
0:25:10 > 0:25:12then eventually the atmosphere could potentially
0:25:12 > 0:25:14get physically stripped away.
0:25:14 > 0:25:16Let's assume that this planet has an atmosphere
0:25:16 > 0:25:19and it's a benign atmosphere, it has liquid water -
0:25:19 > 0:25:22what sort of life do you think could possibly live on this planet?
0:25:22 > 0:25:25Well, I think we can fairly safely say it isn't going to look
0:25:25 > 0:25:27exactly like life on Earth.
0:25:27 > 0:25:30And one of the things that I think you're very unlikely to see
0:25:30 > 0:25:33are lots of beautiful green, leafy plants.
0:25:33 > 0:25:34If there is any kind of plant life,
0:25:34 > 0:25:36it's likely to be a different colour.
0:25:36 > 0:25:40And the reason for that is that plant life on Earth has evolved
0:25:40 > 0:25:43to take advantage of exactly the kind of light
0:25:43 > 0:25:45that we receive from the sun.
0:25:45 > 0:25:49Now, the star Proxima Centauri is a much redder star than the sun,
0:25:49 > 0:25:54so it puts out much more light in the red part of the spectrum.
0:25:54 > 0:25:56It also puts out quite a lot of infrared radiation
0:25:56 > 0:25:58that we can't even perceive.
0:25:58 > 0:26:03And so that means plant life on that planet, if there is any,
0:26:03 > 0:26:06it could look red or it could even look black or grey.
0:26:06 > 0:26:09What do you think the probability is of going there?
0:26:09 > 0:26:11I mean, there are really exciting projects like Starshot.
0:26:11 > 0:26:13Do you think we'll ever get there within our lifetime?
0:26:13 > 0:26:15I think, actually, it's possible,
0:26:15 > 0:26:17and that's the first time I've ever thought it's possible,
0:26:17 > 0:26:19which is why I'm so excited about this.
0:26:19 > 0:26:23The thing about Starshot is that, unlike most of the ideas
0:26:23 > 0:26:26that are thrown around about interstellar travel,
0:26:26 > 0:26:30there aren't actually any hard theoretical barriers to doing that.
0:26:30 > 0:26:32It is theoretically possible.
0:26:32 > 0:26:37It's a technological challenge, but it's perhaps of a magnitude
0:26:37 > 0:26:40similar to challenges we've already overcome as a species.
0:26:40 > 0:26:43I can see why you're excited. Yes!
0:26:43 > 0:26:46Well, thank you. That's been fascinating. Thank you.
0:26:48 > 0:26:50Well, Maggie, you're the engineer here.
0:26:50 > 0:26:54Do you really think this idea of an interstellar probe is possible?
0:26:54 > 0:26:55I'd like to think so,
0:26:55 > 0:26:57but the problem is the stars are so far away,
0:26:57 > 0:27:00so the technical challenge is quite huge.
0:27:00 > 0:27:02But looking at the theory, it does seem viable.
0:27:02 > 0:27:04It's an exciting solution as well.
0:27:04 > 0:27:06It's like something out of science fiction -
0:27:06 > 0:27:10we have a giant laser pushing this probe towards the stars.
0:27:10 > 0:27:12It's a wonderful story to tell.
0:27:12 > 0:27:14It is. And I think it's going to be expensive,
0:27:14 > 0:27:15but I think it might be worth the effort.
0:27:15 > 0:27:18Space science is great at doing miniaturisation,
0:27:18 > 0:27:20and this space probe is going to have to be tiny,
0:27:20 > 0:27:22have an onboard camera, a transmitter
0:27:22 > 0:27:24to send information back, and so the technology
0:27:24 > 0:27:25that goes into that can help us all.
0:27:25 > 0:27:28Yeah. I suppose if we've got one of these things
0:27:28 > 0:27:30to go to Proxima Centauri we can send them to other stars
0:27:30 > 0:27:34with other planets, we could shoot around the solar system as well.
0:27:34 > 0:27:36I do find the cost difficult, though.
0:27:36 > 0:27:39From a scientific point of view, I think there's probably
0:27:39 > 0:27:40other places to spend the money.
0:27:40 > 0:27:42But the inspirational value is great.
0:27:42 > 0:27:44Knowing that that planet's there,
0:27:44 > 0:27:46it would be sad if we weren't trying to get there, don't you think?
0:27:46 > 0:27:49I think so. It's our next-door neighbour star,
0:27:49 > 0:27:51it's got something that looks fairly earthlike -
0:27:51 > 0:27:54we've just got to go there, and this seems like a good way of doing it.
0:27:54 > 0:27:57Yeah. Just knowing the probe is on the way would be so exciting.
0:27:57 > 0:28:00Well, that's all we've got time for this month,
0:28:00 > 0:28:03but do make sure you check out the star guide, which is on the website.
0:28:04 > 0:28:09We'll be back next month with a final update on the Rosetta mission,
0:28:09 > 0:28:12including the latest exciting images that reveal the fate
0:28:12 > 0:28:16of the Philae lander that disappeared on the surface
0:28:16 > 0:28:18of a comet nearly two years ago.
0:28:18 > 0:28:21But, in the meantime, get outside and...
0:28:21 > 0:28:22get looking up. Goodnight.
0:28:53 > 0:28:57You see clips of a pile of bricks causing anger in a gallery.
0:28:57 > 0:29:00And a pickled shark floating in a tank.
0:29:00 > 0:29:02Then a voiceover asks you...
0:29:02 > 0:29:04"Is art just an idea?"
0:29:06 > 0:29:08BBC4 gets very conceptual.
0:29:08 > 0:29:09Three nights of programmes...
0:29:12 > 0:29:12That's my shower!
0:29:12 > 0:29:12I shan't have dirty old men abluting in it.
0:29:12 > 0:29:14Laughs galore on BBC Four.