Life, The Universe and Everything

Live from Cambridge, the search for planets around other stars, mapping the Milky Way and the prospects of life in outer space.
03 December 2013


Live on location at the Cambridge Science Centre, Chris Smith is joined by guests Didier Queloz, who discovered the first exoplanet, Alan Tunnacliffe who investigates organisms which might be able to survive in space, and Gerry Gilmore, who is aiming to map the Milky Way. Together they pit their wits against the assembled public as they go on the hunt for alien worlds and life in space. Plus Dave Ansell and Ginny Smith reanimate yeast, spin an alarm clock to demonstrate how planets make stars wobble, and launch their own hydrogen rocket...

In this episode

02:29 - Searching for extrasolar planets

Looking for planets around the stars of the night sky

Searching for extrasolar planets
with Didier Queloz, University of Cambridge

Chris -   Hello. Welcome to the Naked Scientists at the Cambridge Science Centre. I'm Chris Smith and this is another of our live events. Welcome! The whole point of these programmes is that this is where you, the audience become the interviewers. It's your opportunity to give our guest panel - who we will meet in a minute - a really good grilling. This week, we're going to talk about space science.  All of our guests this week are connected in some way by the field of space or space science and space exploration.  It's quite pertinent because in recent years, we've actually heard stories about people planning to mine asteroids.  We've also heard about people trying to build a hotel, an orbiting hotel, in space.  We've had a call for people to join a manned mission to Mars. They don't want elderly people though.  It's amazing the lengths the government will go to to cut the care in the community bill.  And more recently, they've actually announced just last week, a proposal was put forward to build a barbers on the moon.  It's going to be called E-clips. It is of course nearly Christmas time, but there is some concern this year over whether father Christmas is going to be able to make all his deliveries because there was a bit of a slay accident recently during a test flight.  Father Christmas collided with an asteroid and NASA did catch this with the Hubble space telescope and when they first saw it, they said they think it's a UF ho! ho! ho!  Of course, during this programme, we will be obeying all of the laws of physics.  Very important because the penalties for not doing so are extremely harsh.  In fact, just a famous astronaut Buzz Lightyear discovered when he broke the laws of gravity, he got a suspended sentence.  Let me introduce our panel.  Please welcome this week, we have with us, Didier Queloz.  He is from the Cavendish Laboratory.  We have sitting next to him, Alan Tunacliffe who is from Chemical Engineering and Biotechnology, and Gerry Gilmore is on the end.  He's from the Institute of Astronomy.  They're our panel this week.  Sitting primed on their experimental bench, Ginny Smith and Dave Ansell, who will be doing lots of exciting interactive demonstrations and experiments for us.  Let's kick off with you Didier because you're famous for having discovered the world's first exoplanet.  So, you're going to tell us what one of those is.

Didier -   Yeah.  Well, it was almost 20 years ago and first of all, I think we should start with the beginning.  I mean, what is an exoplanet?  So, we have planets in our solar system orbiting our sun and the next question is, we have plenty of suns everywhere.  We call them stars.  The next question is, what about the planet orbiting these stars?  So, these planets that now we have found: there are about 1,000 of such objects found.  We call them exoplanets, and that's my work.  I'm trying to understand this object, detect them first, and then to try to understand how they form, and how they are.

Chris -   Let's put some numbers on this.  So, in the universe, how many stars are there, apart from Rod Stewart and Tina Turner or Elvis?

Didier -   It's difficult number to capture because the universe is so big.  So, it's difficult to figure out. We have galaxies; it's the biggest structure that we are in, and that's about 100 billion stars.  So, in the Universe, there are zillions of galaxies.  So, it can make up of a very, very big number here.

Chris -   With that very, very big number, how many planets might there be around all those different stars then?

Didier -   Well, it was a big question 20 years ago.  We had only our own planets at that time and the big question is, are we unique or we part of a more bigger set of planets?  So, I think we have clearly answered this question.  There are planets almost everywhere and it's pretty common to find planets around other stars.  What is a bit more difficult here is trying to understand what they are like because as of today, we have not really found a planet or a system like our own solar system.

Chris -   Like the Earth is what you mean.

Didier -   We have found kind of object that look like the Earth, but they're not really exactly like the Earth.  That's a big problem then.

Chris -   How do you find them?

Didier -   Well, I think here, this is a good time for the experiment.  So, the problem we have with the planets is a very simple one.  I mean, the planet is orbiting a star and the star is extremely bright.  So, you could take any means to make a picture, you will only see the star.  So, you have to find tricks to try and see something which is almost invisible.  So, in a practical sense, when you have the planet orbiting the star, what you do have - and this nice experiment here - because the planet is very light, Jupiter, which is the biggest planet we have is only one thousandths of the weight of the sun.  So, it's very tiny.  Then when you have the planet orbiting the stars, what you do see here is practically, all the system is orbiting around what we call the centre of gravity of the system which is in the case of the sun, almost in the middle of the sun.  It is still inside the Sun, but it's a little bit to one side.  So, there's a tiny motion that the sun is doing, by the fact there is a planet.  So, you do obviously see the motion of the planet; that is what we call an orbit.  We know that the Earth takes one year to go around the sun.  But because of the Earth, the sun is doing a tiny bit of motions and then these motions, this is what we have been using to detect a planet.

Chris -   So, when you said there's a little bit of motion, the sun wobbles backwards and forwards a little bit because the planet going around it exerts a gravitational influence on the star.

Didier -   That's a perfectly the right way to explain this. Exactly.

Ginny -   So, we're showing this over here.  Dave setup this wonderful example.  It's not quite what you'd see if you had an actual star in an actual planet.

Chris -   It's a door knob on a stick, is it?

Ginny -   Yeah.  So, we've got a nice gold door knob to represent the sun - shiny, bright, and we've got - is that ping pong ball on the other end?

Dave -   It's a ping pong ball, yes.

Ginny -   We've got a ping pong ball on the other end of a stick.  What Dave is doing is he's got that on a piece of string and he's spinning it.  You can see that this means that the ping pong ball is going round and round the door knob.  The piece of string isn't ending up in the middle of the stick like you'd expect if it was a similar way to both ends.  It's actually orbiting around the centre of mass.

Dave -   So, this means if you look at the door knob, the door knob is wobbling in the same way that the sun is orbiting because the Earth is orbiting it.  There isn't actually a stick between the Earth and sun of course, but the physics is very similar with gravity and the stick in this particular case.

Ginny -   So, the sun is actually doing a little bit of orbiting itself.  This seems very simple with just one planet.  I can imagine it, it must get very complicated if there's more than one?

Didier -   Yeah, it's a bit like a watch after.  I mean, we have the needle that takes the hours, the other one, the minutes, and then the second.  So, like watch, you can read through it if you have enough time to watch the whole motion of all system.  That's what we need to do if we want to capture the longer period system.

Chris -   What do you use to spot these wobbles?

Didier -   Okay, that's the second big question because what we have seen here is the principle of the motion.  But the problem is, what do you do to detect that motion.  That's not at all obvious.  So, a single trick that we can use, which is related to the light - I mean, the light is about like the sound.  It's a wave.  If you move an object, the sound will change.  So, if there's a tiny difference in the wave, we can see there's a change of colour and then because of these motions, this would create kind of a tiny change in the colour in the waves.  So, we can see this experiment.  I just tried to show this instead of having the light which is just too fast, but using the sound.

Ginny -   So, we've got another really high tech experiment for you here.  We've got a ball of bubble wrap with some kind of alarm inside it, you said?

Dave -   It's a buzzer I bought this afternoon.

Ginny -   So, we've got a buzzer in some bubble wrap and we're going to put that in a canvass bag.  You can see how high tech this is.

Dave -   So, it's going to make a horrible noise.  I'm going to explain what I'm going to do first before I turn it on.  I'm going to whirl it around my head and if you listen to it, you should be able to hear a slight change in the pitch of a sound as it goes around.  So, let's turn it on.

Ginny -   I'm going to get out of the way because I don't fancy being hit in the head.


Ginny -   Did everyone hear that?


Dave -   So, as the bag is moving towards you, the pitch went up slightly and as the bag moved away, the pitch went down.  As Didier was saying, the same thing actually happens with light.  The physics is slightly different because Einstein and relativity gets in the way.  If it's moving towards you, the light gets slightly blur.  If it moves away from you, the light gets slightly redder.

Didier -   That's exactly what we're doing.  We're just detecting this, but then it's a tiny change of the light.  That's pretty tough...

Chris -   You're not using a shopping bag.

Didier -   No, we don't use that.  I mean, this is where the difficulty here because we're talking about tiny motions and digging up such a tiny motion - I mean, if you take Jupiter for example, it's the speed of the running man.  So, it's very tiny compared to the speed you encounter in space.  So, it's really tough and then the equipment that we needed to build to measure the speed change - I mean, couldn't be built before, so we had to wait so long to build this such first experiment that was doing that and that's what happened 20 years ago.

Chris -   So Didier, you've said very nicely how you detect these planets.  How do you work out whether a planet is, say, like the Earth or not?

Didier -   Yeah.  That's another aspect of the detection.  So, in some case, you can be lucky enough to have the orbit of the planet, crossing exactly the disk of the stars and it's called a transit.  This transit, it's a kind of a shadow that is produced by the planet on the stars.  So, you don't see the shadow itself because the star, we don't resolve it, so we don't any picture of the star.  But you see a tiny change in the light of a star, like if you have clouds passing in front of the sun during the day and you don't really see the clouds, but you feel that there's a tiny difference in the light.  So, it's exactly the same and from that slightly drop of light, you can get the size of the planet.  So, if you can get some way to weigh the planet, the technique that was described before called the Doppler technique and some wave to size the planet, so you get two very fundamental parameters of the physics.  One of them is the mass and the other one is the size.  So, if you get the mass and the size, you can build something which should be magic which is called the density.  With the density, I can tell you whether it's like the water, whether it's like a gas, or whether it's like a rock.

Chris -   Okay, let's take some questions.  So, you need to get your thinking caps on for your questions.  What have you got in the email, Ginny?

Ginny -   So, I've got an email in from John Black who actually picks up exactly on what you were just talking about.  So, he asked, if you're using that kind of method to detect planets that are travelling in front of a star, so you're looking for the shadow, does that only work for planets that happen to line-up with the telescope and the star?  Can we find out about other planets that don't line up?

Didier -   Well, yes.  You have to be lined up to get the shadow effect.  Otherwise, you don't get the shadow.  But there is something interesting which is called the phase effect.  I mean, we do see the light from the moon changing because the position of the moon is not the same.  It's not the same light from the sun.  So, you do have such effect as well on other planets.  So, you don't need exactly to have a transit, but at some time of the planet, the planet gets a lot of lights and the other time, the planet show you only the dark phase.  So, if you have good telescopes, very accurate because this is a very tiny change, you can see that.  It's called the phase effect and it's where to probe the clouds on the planet.  In that sense, we do a little bit of weather on these planets by doing this way.

Chris -   Amazing!  Let's take your questions.  What's your name?

Helen -   Helen.  I'm from Cambridge.  You were saying, of the exoplanets that we've found, how big is the largest group that all going around the same star?

Didier -   We have a lot of what we call the multiple systems and what we do see is when we have small planets, because we're finding small planets between the Earth's mass and Neptune's, they are very all fine with others.  So, we have really a series of what's called compact systems made of many planets.  So, I think the system that has the most planets is maybe 6 or 7 of them.  It doesn't mean we have found all of them.  We just usually find the easiest one which is the one we know by the stars.  So, there may be much more, and we clearly do not know how many planets maximum we can give in a system.  But it just depend on the mass and there's a lot of mass in the planet at the beginning when you form a system.

Kyle -   My name is Kyle.  I'm from Cambridge.  Is there any way to tell if say, they's a like liquid within a solid, like a lava in the centre of the Earth?

Didier -   This is a very good question.  So, we would love to know this.  I mean, the only thing we can do right now is to get broad perceptions whether it's a big planet like Jupiter made of gas or if it's a rocky planet like the Earth.  Now, if you start to mix up all the thing together, you cannot have a mix of everything because you can have a planet that have a core.  That could be very heavy like the iron core and then you have what's called an envelope which is a big glass.  It's like the lava you have on the Earth.  Then you can have an atmosphere that could be made of water.  You can imagine a planet that doesn't exist in our solar system where you have a huge, huge, watery oceans that's not only 10 km, but it can be 500 km.  So, we can have a lot and lot of many mix to ways to build your planet.  So, answering exactly your question will take some time.  We designed an experiment right now to trying to probe and to detect some - what's called feature, what's on the surface of the planets.  I'm trying to exactly know that because the water for this reason is kind of a training prospect to get water on other planets.

Chris -   You're listening to a special edition of the Naked Scientists recorded with this amazing audience at the Cambridge Science Centre.  My name is Chris Smith and with us this evening, Ginny Smith, and Dave Ansell, our experimentalists, and our panel of esteemed experts.  We have Didier Queloz, we also have Alan Tunacliffe, and Gerry Gilmore.  In a second, we're going to be finding out about life in outer space and what can survive the rigors of space.  But right now, we're talking with Didier about finding exoplanets.  Ginny, what else have you got on the email there?

Ginny -   So, I've got an email in from Angelita Mills who wants to know why poor Pluto was demoted from being a planet.

Didier -   This is a very interesting question.

Chris -   Let me take a vote on that first.  I mean, who thinks Pluto deserves to stay as a planet?  Overwhelming response.  I'm just very disappointed.  Were you disappointed when Pluto got demoted?  Yeah.

Didier -   So, I have to tell you why then.  We have to go back with the history of the solar system.  It's a very fascinating story.  You have to realise that for a long time, the knowledge of the planets was only related to the capability to see the planets by the eye.  And then it took a long time to move away from that time with the telescope and it expanded and we get Uranus and then using Uranus, you detected Neptune.  And then it took quite a long time for people to figure out exactly what was next.  And then the problem of Pluto is, it's not alone.  I mean, the region of Pluto had been probed when Pluto was been discovered, but they also probe other systems, other planet at that time that was demoted as a planet.  One of them is called Vesta or Ceres.  This was a planet.  These are objects that are as big as Pluto there.  So, all these objects are not planets at all.  So, Pluto is exactly the same situation because it took a long time after to figure out that there are other kind of object like Pluto.  So, the problem is then, what do you do if you start having not only 1, 2, 3, but hundreds of systems like that?  And that's these hundred systems deserve a specific name which is called the transneptunians.  So, if we want Neptunes that is not only Pluto, there is tons of object and that's the reason why at some point, we have to decide what we do there.  Do we continue to count them?  And then we ended up with 100, 200 of such object, or do we define a planet as an object that is kind of isolated?  And that's exactly what happened in these big discussions.  So, people have agreed that at some point, to qualify as a planet, it's a bit tough discussion, but it's kind of clean.  It has to clean everything around it.  So, there are other objects that you find between Mars and Jupiter.  It's called the asteroid belt.  So, it doesn't qualify as a planet and that's the reason why Pluto has been demoted.

Chris -   Now that's an astronaut's favourite music, Neptunes.  Question down here...

Paul -   Hello.  My name is Paul from Cambridge.  If we're looking for planets, I suppose that's probably because we all know what a planet is, but have you, in your searches found anything that's very different to what you're expecting?

Didier -   Well, I think we have been surprised from the beginning and we keep being surprised.  The reason why is that when we started all these, we have this obvious mental picture of solar system planets.  And all the planet that we're finding are very different.  The first one was a big Jupiter, very close to its stars.  Kind of a burning world.  So, there is no counterpart for these systems.  We have what's called super Earth.  It's kind of a very rocky, very hot planet, kind of different from the Earth.  We think that this is a big core of rocks and with a atmosphere of lava.  And again, it's a big surprise.  So, they all have planets, but they are not the planet the way we see it in our solar system.  I think this is just the beginning of the story.

David -   David from Cambridge.  If we were to hypothetically position ourselves and the nearest star in our galaxy, and using technology that we have available today, look towards our own solar system, what would we be able to understand about our solar system?

Didier -   I think today, we would not see anything because we're just on the verge to detect a system like our own.  We have found a lot of other systems and the interesting part of it is, we know that from all the system that we have found, that the vast majority of the stars, they did do have such a system.  So, we know already that the solar system is not the vast majority of the other planet.  But it doesn't mean that there is not such a system.  So today, we would just fail.  The big problem we would have is, Earth is very tiny and then even Jupiter will be a big problem because to get Jupiter, you will need to observe our system long enough and then you would face the activity of the sun.  There is a solar activity, it's a life cycle, and we know that the sun, when there is a high activity level can be pretty active.  A lot of spots on the sun and that prevent us to really do something good to the big planet.  So today, I must admit that we will just miss the solar system.

Chris -

That's reassuring, isn't it? No one is visiting too soon. Ladies and gentlemen, Didier Queloz.

19:01 - Dehydrate to survive!

What sort of creatures might be able to survive in space? Alan Tunnacliffe explains it might be those who can live without water...

Dehydrate to survive!
with Alan Tunnacliffe, Chemical Engineering and Biotechnology, University of Cambridge

Our next guest is Alan Tunnacliffe who is from Chemical Engineering and Some yeastBiotechnology at the University of Cambridge. He works actually on things that can survive in really quite bizarre environments,  including space.

Alan - Well, we work on organisms, creatures, that can survive desiccation. So, that means they can dry out, they can lose essentially all their water, and that sounds like a pretty bad  thing to happen which it would be for us, we'd die pretty quickly if we started drying out. But there are some creatures that can do this. They can lose all their water and survive and then you just add water again and they  come back to life and carry on as though nothing had happened.

Chris - What are they?

Alan - A wide range  of things - lots of microorganisms, lots of bacteria , yeast for example, which you might see a little bit later on or perhaps....

Ginny - Yeah, in fact, let's get it setup now. So, we're going to show you how you can bring some animals, some creatures back to life. So, we've gotten these little pots, just some normal fast-acting bread yeast and a little bit of sugar to give them some food. What we're going to do is we're going to add some water to them, rehydrate it, and we've got them in film canisters. Now, young people amongst you might not recognise these. They're remarkably hard to get a hold of these days,  now, everyone has digital cameras. This is what you use to get film in and they're very useful for science experiments.

Dave - So, I'm just filling them up with water nicely. I'm going to put the lids on and then we will leave them for a bit. See if we can reanimate that yeast.

Ginny - So, we've given them some nice warm water and we're going to put them in the bath of warm water. Do you want to put the bowl on the front just so no one can miss it if something exciting happens?

Chris- I'm glad it's in front of Alan. So, these creatures that can do this, why have they evolved to dry out?

Alan - Well, it's part of the natural environment. If you think about a yeast living on a surface of some fruit, then they're going to experience drying conditions. It's quite hot in the sun, the wind blows around them and takes all the water away. So, they need to be able to cope with this low level of water and survive.

Chris- So, when something does dry up, what actually happens to the organisms when their cells lose all their water?

Alan - Well, we need water to have any biology at all. So, they basically shut down.  They go into a state to suspend the animation. It's as though they - they even stop ageing. So, animals will do this and they have a natural lifetime and when you dry them, that stops and they stop ageing at that point. When you rehydrate them, they will continue ageing and then they will live out what's left with their natural lifespan after that point.

Chris - So, what is the relevance of these creatures to space?

Alan - Good question. The point is that there's not much water in space. So, if you were thinking about organisms moving from one place in the solar system to another, from Earth to Mars, or the other way around perhaps, an organism like a yeast is not going to build itself a spaceship. So, it needs to be able to survive that journey without the presence of water. So, if it can survive drying, there is a good chance it'll be able to survive the journey through space because the other thing that happens when you have this drying process, when you get this sort of shutdown of all the biology in the organism, is they become very resistant to stresses. So, a dried yeast for example is able to survive vacuum as in space. It's able to survive very, very low temperatures even close to absolute zero which you'd  find space. So, that's exactly what you would like the organism to be able to do to become very stress resistant.

Chris - A lot of radiation in space though, doesn't it?

Alan - Yes, that's the problem. So, you need to be able to shield the organism from radiation, but that may be possible.

Chris - Dare I ask, has anyone actually tried seeing if there are organisms capable of surviving in space?

Alan - Yes, indeed. So, people have sent up various organisms. For example, bacterial spores and some dried little animals of the type that that we work on, water bears and rotifers and things and you can put them on satellites or the   International Space Station and have them exposed to space conditions. There have been bacterial spores going around the Earth for several years and yet, surviving that process. So, they can survive.

Chris - So, it's like C. diff can survive in the hospital and these things can even survive in orbit. So, when NASA and other agencies, say, they take steps to make sure that what they put into space and sent to Mars doesn't pose a microbiological threat - in other words, they go to enormous lengths to clean satellites and other objects off, then that's reasonable practice.

Alan - Yes, if you don't want to contaminate the environment that you're visiting, it's a good idea to do that.

Chris -   Ginny...

Ginny - So, I've got a question here. Alan Scott who actually got in touch on Facebook and he asked, "Could we engineer DNA to send to a planet if we found one with the right conditions? Would it survive and could it then seed life?"

Alan - So, yeah. If you take the right steps to protect the DNA from radiation as we just heard, you could in fact get DNA from one place to another.


Chris - I think out experiment just worked

Alan - It didn't quite launched into space, but it's...

Chris - Now, it looks like Alan has thrown up on the table in front of him. Ginny, what's going on?

Ginny - So, what happened...


Chris - There's the other one.

Ginny - I'm just going to pass some tissues to our guests so they can tidy up if they need to. So, what happened there? Well, our yeast was coming back to life. Once it had the water in there and had some sugar, it could rehydrate. It could start to grow again. What yeast does when it grows is it produces a gas. So, it's produced carbon dioxide that's built up in this little film canister and then film canisters are pretty good. They can keep quite high pressure, but at some point, they can't hold it in anymore. The lid popped off and we got a nice big explosion.

Dave - A fountain of yeasty broth.

Chris - So, there's one theory Alan that says, that life got started here on Earth because something delivered life to Earth. Do you believe in that?

Alan -  It could've happened. People talk about the life on Earth arriving too early in a way. It may be as much as only 500 million years after the Earth was formed and some people think that's too early. So, how could that have happened? Well, we might got a helping hand by life being seeded from elsewhere, perhaps from Mars.

Chris - Is there any evidence that things could get into rocks and things and then survive being blasted off of  the surface of one planet across space and then land on another and not get destroyed?

Alan - Not quite that, but people have done experiments with bacteria which have been buried inside rocks and they've tried to mimic what would happen if you had a meteor impact and blasted that rock into space. People have shown that the bacteria that they've used survived that process. So, possibly, yes.

Chris - Anyone got any questions?

Jeff - I'm Jeff also from Cambridge. What's the largest size of creature that can survive being dried and brought back to life again?

Alan - There's a creature called polypedilum vanderplanki which is basically...

Chris - Easy for you to say.

Alan - Well, it's not a very attractive organism in a sense, it's just a midge,  just very boring, but it's interesting. It comes from Africa and its larval stage is able to survive desiccation.  The larvae are quite big. They're about ½ cm in length, something like that and that's the largest one I know of that can survive desiccation. The problem is, once you get larger and larger, there's a physical stresses on something as it dries out. It gets really sort of brittle and crumbly. So, if you tried to do that with say, a human being, we just wouldn't survive physical stresses of drying. We'd just crumble.

Chris - Dave and Ginny have got an experiment coming up......

Carl - Hello. I'm Carl. I'm also from Cambridge. You say that water is necessary for life, but isn't that just life as we know it? Could there be different life in space that doesn't depend on water?

Alan - Absolutely, yeah, I mean, everything we say is from a sample of one, right? All we know about is life on this planet. And so, who knows? There could be other types of life out there.

Ginny - I've got a question in from John Michael Williams who wants to know whether the very high levels of iron on Mars might prevent life there.

Alan - Just looking at what happens on Earth again which is the only example we have, there are lots of organisms that can survive and grow in fact in the presence of elements - lots of iron and other types of heavy elements. They've evolve ways to live with that. So, in principle, no, that's not a problem.

David - David from Cambridge. When I was at school, we were taught that all life derived its energy ultimately from the sun and life wouldn't be possible without that. We've since discovered sulphur-eating bacteria in under sea vents; has this changed our opinion on the chances of finding life in other places in the solar system and beyond?

Alan - Yes, I think it has in the sense that people think about Mars as our closest neighbour and we're interested in the idea of life on Mars because we think there was water on the surface, water on the planet at some point in its history. And therefore, life may have evolved on Mars during its early life. The question is, what happened to it? Well, it's possible that the life, if it did evolve on Mars is still there, but surviving not on the surface, but underground. So, we know that if you look at the Earth again, we can see bacteria which survive, grow, live quite happily several kilometres under the surface of the Earth. So, they live within the rocks and there's enough water there for them to survive and get by, it's a bit warmer down there. Actually, the temperature that it gets very hot as you go towards the centre of the Earth is a limiting factor of how far bacteria can survive down there. So, if you think about Mars then maybe it also gets a little bit warmer as you get towards core. So, there may be liquid water underground. And so, if life did evolve on Mars, there's no reason why it shouldn't still be there, but not on the surface where we're looking for it, but maybe some distance underground.

Chris - Is it possible then that we'll be able to work out how to put humans into a suspended animation state, a bit like they do in sci-fi films, so you can go on long space journeys so that we can head off to Mars or wherever else we want to go?

Alan - Well, not by drying them. That's not going to work. We're actually trying to do that with human cells actually, so you could dry a human cell which you can grow in laboratory but not a whole human being. Maybe you could use freezing instead.  That's probably the best way to go.

Chris - Especially in this weather. Any other questions from you guys?

Helen - Hi. Helen from Cambridge. What's the longest period of time that anything has been desiccated and then successfully reanimated that you know of?

Alan - It depends on the organism. So, if you're thinking about these little animals that we work with which are tiny little invertebrates, anything from 10 to 100 years. But those are only the well-documented examples because you're relying on having museum specimens and so on that you know the age of and that you can look at carefully. There is evidence that some microorganisms, some bacteria may be able to survive for much longer periods. Some people claim even 200 million years which I think that's not really well substantiated. But we're talking about long periods of time, certainly enough time we think to transit between planets in the solar system.

Robin - Hi. I'm Robin from Cambridge. I just have a question with desiccation. Is there any change in the organism in that time when they are kind of shutdown or do you just come back exactly as you were?

Alan - We think that the organism is basically unchanged. For biochemistry to happen which is how things break down, degrade, how you get older, you need water. So, if you take all that water away, those biochemical processes, including ageing and other processes can not take place.

Melanie - Hi. I'm Melanie from Cambridge. All the kind of things you've talked about so far for going between planets, it's kind of just suspended. Do you think there's any chance that you could have life which actively lives not attached to a planet?

Alan - As far as we know it, and we had a question about other forms of life, but the form of life that we know requires liquid water. So, you'd need to have a situation where you could guarantee liquid water. And the temperatures that you find in space are way too low for that to happen. So, you would need a protected environment like a spaceship in order for life to survive in space.

Chris - What about a planet that doesn't have a star and just goes wandering through space because we've found some of those now? I mean, Didier Queloz in the recent month, we've heard a report another one being found of just a planet with no star. It's just wandering through space.

Didier - I mean, we don't know exactly how much they are, all these planets, but clearly, in the mechanism to produce the planetary systems in some cases, we can be unlucky and because of the big interactions between planets, you may have a change in the orbit and some of them can just be thrown away into space. So, there must be such a planet going around that is very cold, extremely cold. That's why we don't see them because they're so cold that they do not emit anything.

Chris - Any other questions from you guys? There's one just at the back over here...

Carlo - Good evening. It's Carlo from Cambridge. I would like to ask, how gravity may affect living forms or is there a gravity range where we believe life can develop?

Alan - People have put living creatures into space in a spaceship - humans of course, but also, other creatures and there are some processes which may be slightly affected so development of the organism from an egg to a fully grown organism might be affected somewhat. But basically, most of the things seem to happen okay. If you were a bacterium, you're probably not going to notice too much that you're in a microgravity environment.

Dave - I guess, the bigger you are, the more gravity affects you. So, the narrower range of gravities which you function on. So, if you're an elephant and you went to some planet twice as big as Earth then you'd have trouble.

Alan - Well, you'd have to adapt to microgravity I think which is the question. And so, if you're an organism which has evolved to live on a planet with significant gravity, you're going to find it quite difficult. Astronauts that go into space have problems with their bone density and muscle tone and so on. So, yeah it would prove quite challenging I think.

Chris - A weighty question. Anything else from you guys?

Brian - I'm Brian from Cambridge. When we send an astronaut up into space they have a closed environment for maintaining water in, is that 100 percent? Is there a limit to how long you can send an astronauts into space, preserving the water they've got or do you need to send up a water supply to keep them going?

Alan - Gosh what a great question. So, I imagine, you could do this for quite a long time, people are talking about very long missions indeed, missions to other stars and things. To do that, you would have to be able to recycle your water and maybe yes, even regenerate it to some extent.

Sam - I'm Sam from St. Ives. If there was a planet with an atmosphere with gravity, if the planet moved, would the atmosphere move with it or would it stay in a cloud?

Chris - That's one for you Didier.

Didier - Actually, because the gravity, the atmosphere, it's a bit like Earth. It's a bit difficult to get out of these planets. We need a rocket to get out of the planet. So, the atmosphere is kind of glued by the gravity to the planet as well. It's exactly the same. The only part of the atmosphere that can get away if you have a very light molecules and some of them maybe hydrogen or maybe helium which is used for balloon and then just this one can just escape in some conditions. But most of the gas, they're just trapped like us to the planet.

Alan - Can I just ask a question, Didier?

Didier - Are you allowed to do that?

Alan - This is the only chance I'm going to get to ask this question. So, gas is escaping from the planet, right? So, why doesn't our atmosphere just all disappear into space?

Didier - It's a matter of two actions. One of them is called gravity. So, if you get the planet light, not strong enough, we don't have gravity then we're going to lose the atmosphere. It's a bit like what happened with Mars which is a very small planet compared to the Earth. And then the other situation when you can get trapped is you're too close to the sun, but then there is interaction in the upper atmosphere between what's called the solar wind. Because there is interaction, the sun is producing particles and not only radiation but also particles and then you interact.

It's like blowing wind that slowly kind of grind and blow out the atmosphere. If the atmosphere is very thick but the planet is very close, if you get enough time, it can completely peel off the atmosphere and we do believe that we have known some very wierd, you may have heard of a planet, rocky planet made of lava orbiting the star in one day. So, they're so close. I mean, they can almost touch the stars and we do believe that these planets must've been bigger and kind of have lost their atmosphere because of the impact of the sun.

Chris - Lovely! Any more questions?

Victoria - Hello. It's Victoria from Cambridge. If we're talking about exophiles and changes in pressure, if we took some of the bacteria and the creatures that are living in hydrothermal vents deep under the sea, and we brought them back up to the surface, would they survive or would the change in pressure be too great?

Alan - That is a problem. These so-called barophiles, these organisms which like living at high pressures.

Chris - Like in our lab.

Alan - A different kind of pressure. Yeah, if you try to bring them up to the surface where the pressures are what for us are normal, that for them of course, it's not normal. So, you could think about these so-called extremophiles living in these crazy extreme conditions. But of course to them, living there, those are the normal conditions. And what we live in is an extreme environment to them. That's why it's difficult to work on those organisms because you have to try to replicate the conditions that they would normally live to be able to study them.

36:50 - Mapping the Milky Way

The Gaia spacecraft will soon begin mapping out the 3D positions of the Milky Way's stars

Mapping the Milky Way
with Gerry Gilmore, Institute of Astronomy, Cambridge

Gerry -   Hi.  I'm Gerry from Cambridge.  I'm one of those very rare astronomers who actually tries to understand things that you can actually go out and look at at night.  There's not many of my colleagues who do this and most of the time, I don't either.  But in particular, we've got a huge project that's coming into fruition right now.  We're trying to understand the origins of the Milky Way.  So, it's the most basic question you can go outside and answer or ask at least.  Every culture that we know of has its own answer called mythology or gods or whatever name you like, at to, how to break the 'what came first' problem.  Here we are, what was there before us?  And so, the challenge is to say, look up at the sky and you say well, I can see what I can see.  But what's really out there?  What's the Milky Way really made of?  How big is it?  How fast is it moving?  What is there out there that's important that doesn't shine, that we can see?  So, how much does it weigh?  A few basic little home-grown questions like, where did the oxygen that you are breathing right now get created and how did it get here from wherever it was formed?  How is the stuff you're made of got to be around so that you can be made of it?

Chris -   Can you give us a few stats on the Milky Way?  In other words, where we are in it, how big it is, how many planets and stars it may have, that kind of thing.

Gerry -   Well, that's really what this project I'm going to talk about, Gaia, is going to answer, but our approximate number at present, the Milky Way is made of roughly 100 billion stars of which the sun is pretty typical.  The sun is about 30,000 light years from the centre of the Milky Way and the far outer reaches of the Milky Way that we still think of as the Milky Way are about a couple of hundred thousand light years from the centre.  So, the whole shows 300 or 400,000 light years across.  It's a big thing.  It's made of a hundred million stars, but mostly, it's made of dark matter, about 90% of the sun is stuff that's not the same as what you're made of.  It's something mysterious that we know nothing about except that we can weigh it.  And we know that a star like the sun which is made of the same sort of chemistry that you're made of is pretty typical.  And so, most of the stars and planets are made of the same sort of chemistry that you are.  But some parts are made of quite different things, really primordial stuff that's left over from the very early stages of the Big Bang.  And so, that also tells us how old the Milky Way is.  The whole universe is about 13 billion years old and it's pretty clear that the first structures that eventually came to form what we now call the Milky Way were already in place a few hundred million years after the very beginnings of the universe.  So of course, it's even older than that.  The hydrogen in the water that you're made of was created in the Big Bang.  And so, in a very real sense, you are a fossil of the Big Bang itself.

Chris -   Do you think the water companies will kick in and try charge us for that? Bills are going up!  So, one question though.  If you've got all these matter which is coalescing into stars in this galaxy, why does it spread out into separate little stars?  Why doesn't it just form one massive blob of matter?

Gerry -   Well, it's because the universe is a big place actually.  The challenge in astronomy is not to stop everything forming one giant thing which will be a giant big black hole.  It's quite the reverse.  It's how to get it in close enough that had actually has stars so that you can see them in the sky.  In the very early universe, the whole universe was very uniform, but it was noisy because of the Big Bang.  And the sound waves, there really were sound waves.  There really was a bang.  The sound waves pushed the matter around and allowed to accumulate and then fall together.  So, good old gravity, the dominant force in the entire universe eventually brings stuff together.  But ordinary matter, ordinary gas and so on doesn't like being in a small place.  It's really hard for it to cool down and collapse into a small place and then form stars.  So, to do that, first of all, you need chemistry to cool the matter.  So, you get this chicken and egg problem.  If I don't have any chemistry to form the first stars, how do I form the first stars?  That's a question that we're thinking about right now.  But then other things do form stars, but the thing that stops it all going crazy is again, the dark matter.  The dark matter dominates the weight and the mass of everything.  And there's so much of it that all the stuff in the universe is whizzing around quite fast.  It's whizzing around so fast that it never gets a chance to accumulate into very large pieces.  Largely because one side of a large blob is moving quite fast relative to the other side and it just shears itself apart.  So, if I try to put all Milky Way together into a single thing, it would rapidly fragment again into what we see.

Chris -   One physicist put it to me that the only reason that dark matter got invented is so you could put the word dark in front of it.  It sounds sexy and you get more grant money.  But there we are.

Gerry -   That's true for dark energy.  It's not true for dark matter.

Chris -   Tell us about actually what this Gaia project is.  How are you trying to map out the Milky Way and understand it?

Gerry -   So, Gaia is the name of the satellite that gets launched on December the 19th about quarter past 9 in the morning.  You'll read about it in the news that day hopefully as a wild success and triumph for 25 years of my life.

Chris -   We noticed we were recording the programme before the launch of Gaia, just in case because otherwise, we wouldn't be able to use Gerry on the show because he would've been talking about the satellite that wasn't.

Gerry -   And otherwise, you'd be hearing sobbing noises, but it's going to work.  It's astonishing technology actually- just blow your socks off.  But the real thing that Gaia is going to do is take the first ever census of the Milky Way.  At present, we can't do that.  We can take pictures of the sky and count the stars, get this 100 billion number.  By eye, you see about 6,000, so that's a teeny fraction of what's really out there.  But we don't know where they are.  We don't know how far away they are.  The hard thing in astronomy is measuring distances.  There's only one way we can do it and that's by using a triangulation technique called parallax that - here's an experiment that all your listeners should be doing right now.  Hold your arm out in front of your face.  Come on audience, hold your arm out.  That's it.  Now close one eye and then close the other eye and you'll see your thumb.  Hold your thumb still and you'll see it apparently jumping from side to side.  Now that's parallax and that tells you- the amount it moves, tells you how far, how long your arm.  All animals have evolved that way so you can find out where the food is, so you can go and catch it.  And that's the same trick we use in astronomy except in astronomy, the distances are rather larger than they are to your nearest dinner.  And so, we need to measure much smaller shifts and that's where we need fancy technology.  And in fact, the scale is such that the distances in the universe are so large that Gaia measures angles who has silly names - nanoradians and things that only a nerd would understand.  But to give you a useful analogy, the accuracy with which Gaia will measure the positions of each star is equivalent to locating a shirt button on the moon.  So, that's equivalent to measuring the thickness of a human hair when you are sitting here in Cambridge and the hair is on somebody's head in Paris.  So, that's the level of precision.  It just blows your socks off, doesn't it?  I mean, it's awesome, this thing.  And Gaia is going to do that for a billion stars.  And so, it's going to provide this 3D map of where these billion stars are.  But it's going to do even better than that because we're going to carry on doing that for 5 or 6 years.  So, we'll see how they're all moving.  So, we not only get a 3D map of where stuff is now, we'll also know how it's moving, so we'll know where it's going to be in the future and we'll know where it came from in the past.  And we're going to do even more than that.  Why stop there?  So, while we're at it, we're going to actually deduce the properties of those stars and work out what chemical elements they're made of.  So, we'll be able to track back the history of the oxygen, the carbon, the nitrogen that you're made of and find out what stars made this stuff and when and where, and how it got to be in our bit of the universe, and how the Milky Way is still forming today.  The Milky Way is still growing.  It's like some people in this room.  Most of us are actually probably either growing or putting on weight. And the Milky Way does it too.  It's getting heavier every day.  It's gobbling up its neighbours, which I hope you're not doing! And so, it gets bigger and heavier, and Gaia will find these.  No matter how cleverly you try and eat your neighbour, you'll always leave a few crumbs around.  Gaia will do the same thing.  At least it'll find the crumbs and the debris of these little satellites that have been gobbled up.  And so, we'll be able to count the things that used to be alive and have now been gobbled and work out just when and where the Milky Way put itself together.

Chris -   Let's take some questions.  So, get your thinking caps on, but in the meantime, what have you got on email there, Ginny?

Ginny -   So, I've got an email from Patrick Monde who says, he's heard about a planet which was inventively named planet X approaching Earth and he wants to know if a new planet did enter our solar system, how would it affect us here?

Gerry -   People spent ages looking for planet X and then they eventually found Pluto and realised they had found plutino X as we heard just before.  And there will be more Pluto-like objects in the far outer solar system.  The way we find them is the way we find anything else.  It's by weighing them.  It's the only way we can find things that we can't see is by weighing them.  And so you say, how can I weigh something if I can't see it?  Well, you didn't say, "Let me tell you about dark matter" but that's a different question.  But the key to the planet X thing is that there are lots and lots of asteroids.  In fact, Gaia will measure very carefully the orbits around the sun of about 40 million asteroids.  And some of these go a long way out.  And so, if there is an extra planet out there then Gaia will notice that all the asteroids coming from that direction in the sky have slightly funny orbits compared to the ones coming from other directions in the sky.  And so, by looking for patterns in the asteroid orbits, we'll be able to tell you what is there or equally, what is not there.

Chris -   That's how a spaceman keeps his trousers up of course, asteroid belt.

Victoria -   Hello.  It's Victoria from Cambridge.  When you talk about the size of the Milky Way, are you talking about it as in like a 2D frisbee or more like a 3D sphere, like how do you picture the Milky Way in terms of size?

Gerry -   All of the above is the answer to that one, aren't I annoying!  The Frisbee picture of the Milky Way is a very good picture of how the stars are distributed.  That is actually very realistic.  We all take it for granted but that's only because we were told that was the answer.  Newton failed to deduce that.  He tried very hard and it was one of his great failures in his life was to try and work out the structure of the Milky Way so he gave up astronomy and moved off to run the Mint.  But about 100 years later, a guy named William Herschel working in the exotic astronomical centre of Slough did actually produce a proper star map of the sky and deduced this Frisbee structure.  And so, the appreciation that the Milky Way is a Frisbee is actually quite modern.  But that's only the stars, the dark stuff, and some of the very oldest stars are actually distributed in a - so, it's not quite a sphere, it's more like a rugby ball shape.  You can tell from my accent I'd go for a rugby balls as an analogy.  So, most of the mass, the real stuff that's out there, reality, is in a big rugby ball shape.  Most of the stars, the uninteresting bits that we can see and you and I are made of, that's in the big Frisbee.

Chris -   You didn't say anything about cricket though, did he?  Who's next?

Jeff -   Jeff from Cambridge.  Can you tell us a bit more how Gaia is actually going to see these things?  Is it a camera?  What is it doing when it's out there for these 5 years, discovering these billions and billions of stars?

Gerry -   Well, there's a famous quote from an American sports coach.  He says, "The best way to find out what there is is look."  And so, that's what we do.  The first simple thing, the only basic step you take at any experiment but especially in astronomy is going to take a picture.  And so, that's what Gaia does.  Gaia is just a gigantic video camera.  There's two telescopes mounted on a big ceramic ring.  It's got two telescopes and these two telescopes feed light onto a gigantic video camera which is the largest video camera ever built.  And so, it's made of CCDs, just like the ones you have in your mobile phone.  Except the ones in your mobile phone have a CCD in them which is about the size of the nail on your little finger.  The Gaia camera is about the size of a large desktop.  It's over a meter long, half a meter wide.  It's got a billion pixels.  So, it's the biggest camera ever built.  This billion pixel camera is just going to be taking pictures.  Doesn't it sound easy?  And beaming the information down to us for 5 or 6 years.  Now, from these pictures, we can measure how bright the star is and where it is.  If we keep doing that for 5 years, we'll see everything moving. And the dominant movement that we see, actually, the second most important movement that we see to be technically correct, is this parallax which is the distance to the star.  So, the second thing we measure is distance to a star.  The first thing we measure, the dominant thing, the most important thing is actually general relativistic light bending by the sun which is a really big effect compared to measuring the distance to a star which is a long way away.

Kyle -   Hello.  It's Kyle from Cambridge.  How long will it take for it to analyse one star?  And before the Big Bang, what was there and how did it get there?

Gerry -   Okay, I think that's two questions.  The first question is that Gaia will be measuring stars at the rate of about 40 million stars per second and it'll carry on doing that for 5 or 6 years.  So, Gaia is going to measure about a billion stars.  It's going to measure each one of them about 100 times.  So, it's going to make 100 billion measurements.  That's a big number.  It's quite interesting to think about that number and you think, how long would it take me to get to 100 billion if I clapped my once a second.  You can work that one out.  You'd be quite old and your hands would be very tired by the time you finished.

Chris -   Gerry, how many hard disks is that?

Gerry -   If the data were compressed into minimal format, it's about 35,000 DVDs.

Chris -   So, how are you going to store it?

Gerry -   Well, we don't put it on DVDs.

Chris -   It would be quite interesting to watch.

Gerry -   It would be, yeah.  Modern technology is just amazing actually.  I have a super computer at home near my office which is going to process all the stuff.  And we have petabyte scale storage already.  But the billion pixel camera is actually equivalent to a high definition film and so, what we're doing is just getting a high definition movie running for 6 years.  So when you say it like that, it's not so bad.  I mean, you'd have a hell of a 4G phone bill, but...

Chris -   Do you ever get tempted while you've got the thing on Earth just to take a few snapshots of things?

Gerry -   We did.

Chris -   What did you take a picture of?  Did you do a selfie with it?

Gerry -   Unfortunately, it's kind of hard to get an image when the thing is that big.  So, they're really dull test images, but we know the camera works.  It's also ultrasensitive, so it's a pretty cool piece.  So basically, all this is video and from that, we have to deduce everything.  But we can, we can deduce distances, we can deduce speeds, we can deduce from the colours, we can deduce the chemistry.  And so, we can just setup a clock and say, which bit of the universe formed when and how did it get where it is today?  With orders of magnitude more accuracy than we could do before and including things like finding planets.  Didier finds planets by measuring how the speed changes, or how the brightness changes.  Gaia is going to find planets by actually watching how the sun moves.

Chris -   Well hopefully, on the 19th of December, everything is going to go well.  So, we thought we'd reveal to you some of the technology is going to be involved in getting it up there.

Ginny -   Yeah.  So, we are going to launch our very own rocket.  We're not going to try and send it into space just yet but it works on the same principles as a real rocket.

Dave -   So, sticking to our high technology theme, the basis of our rocket is a standard lemonade bottle.  I've pre-filled this with one of the fuels which are used in the very high spec rockets, which is hydrogen.  So, the top of this bottle at the moment is filled with hydrogen.  We're getting comments from the front which may be working out what's about to happen next.  So, hydrogen is a very flammable gas and it will burn, releasing a huge amount of energy.  When you heat up a gas, it gets bigger and so, we have a bottle with a load of gas which suddenly got maybe 20 times bigger inside it.  We're going to have taken the lid off at this point, otherwise it wouldget very messy.  There's only a hole at one end so all that gas which is expanding, it can only get out in one direction and if I push you, you actually push me back.  If you push anything, it pushes you back, not necessarily the kind of fight way.  If you lean against the wall, it pushes you back.  Otherwise, you'd fall through the wall.

Ginny -   Or if you're sitting on a wheely-chair and you push someone, you'll move.

Dave -   Indeed.  It's a very, very fundamental piece of physics which Newton worked out.  And so, if the bottle is pushing lots of gas out one way, the gas should be pushing the bottle the other way and we should have an interesting effect.

Ginny -   So, there will be a bit of a bang.  So, we're going to need people to put their fingers in their ears.  Don't do it just yet.  I will tell you when to do it.  Dave is going to open up the bottle and let out the water.  What that'll do is it'll let in some air because hydrogen is quite explosive, but it gets a lot more explosive when you mix it with air.  So, we're going to let in a nice amount of air and I'm going to now put my ear defenders on.  And then we're going to put it into our rocket launcher and Dave is going to light the gases and everyone, put their fingers in their ears now...


Dave -   So, that's exactly the same principle which a space rocket works on.  You burn actually hydrogen and oxygen, the same thing we're burning here.  You liquefy it so you get more in the rocket.  It expands, pushes downwards and the rocket goes upwards.  And it works even in space with nothing else to push against.

Chris -   Anymore questions from you guys for any of our panellists before we finish?

Paul -   It's Paul from Cambridge.  In the earlier discussion about planets, it was mentioned that there are some planets we can't see because it's dark and they're not illuminated.  Is dark matter as simple as that or you make it sound very mysterious?

Gerry -   Dark matter is not as simple as that, no.  Some of it is certainly made up from things we can't see, but are like things we know.  In fact, the original experiments to measure the weight of the galaxy and to deduce dark matter took place just over 100 years ago, and they were deliberately designed to count or deduce the number of very faint stars and planets that must be out there that with the technology at the time, they couldn't find.  Gaia will find lots of these planets that we can't see just by weighing them.  But dark matter is different.  We know from a variety of evidence partly from just weighing things like the Milky Way, weighing galaxies, but also from weighing the universe.  From detailed studies of the sound waves and how they propagate through the early universe, that dark matter can't be made of the same stuff as ordinary matter is.  So, ordinary matter, baryonic matter as we call it, the stuff we are made of, makes up at most a few percent of the total mass in the universe.  We don't know what this other stuff is.  The best guess is that it's a variety of families of elementary particles, sort of new Higgs Boson-y sorts of things.  But it might not be.  It might be our theory of gravity is wrong.  There's lots of possibilities going on.  We just don't know what it is and that's one of the key challenges for Gaia, is to do precision weighing.

Wendy -   Hello.  I'm Wendy from Perth, Australia.  Can you tell me how far away from Earth the Gaia satellite will be positioned and once it's completed its mission in 5 or 6 years time, what will happen to it?

Gerry -   The key thing with Gaia is, it has to be maintained ultra precision and stability.  To measure these tiny angles we're talking about, everything has to be absolutely no varying.  So, it's got no moving parts.  It's got to be kept sufficiently cold and stable that the temperature across the whole thing which is about 3 metres across, changes by less than 1 millionth of 1 degree over 5 years.  The way to do that is to keep well away from the Earth and the moon.  Partly to avoid eclipses, partly to avoid gravity as the Earth and moon change, from shaking you around.  And so, real precision satellites and Gaia will be the fourth of these that's done this, go out to a point 1 ½ million km beyond the Earth which is where the gravity from the sun and the Earth and the moon basically more or less cancel out.  And so, it's a nice stable place.  You're far away from the Earth.  You can step off to one side a bit and avoid eclipses so you get no temperature changes.  The sun is always illuminating your solar panels.  You can always see the Earth to communicate with the Earth, but it's nice and cold and stable.  So, there have been 3 previous satellites, two cosmology ones and one infrared one called Herschel that have used this L2 point.  Gaia will do the same, but this L2 point is not actually stable.  It's only semi-stable.  So, if you leave something there for long enough, it'll come and fall on your head.  And these days,space agencies are responsible.  So, when satellites die, they get thrown into an orbit, such that either you know what that orbit is very accurately or that orbit is so far away that you never have to worry about them coming back to Earth.  So, just about 3 weeks ago, the previous occupant of the spot which was the Planck Microwave Background Satellite got thrown out of this place and is now in its own orbit around the sun.  The same with Herschel and the same with WMap, an American one which was there before that and Gaia will do the same thing.  So, in 5 years time, Gaia will become its own satellite of the solar system.  In fact, will be with these other things, artefacts that survive longer than the Earth does.  So, when we come to the end of the solar system, the Earth will be burned up to a cinder, but anyone who came to look would find Gaia out there.

Chris -   Comforting thought isn't it?  One last question.

Mira -   Hi.  It's Mira from Cambridge.  What theory do you believe in like how the Big Bang theory started and how it created everything?

Gerry -   It's a really interesting question actually because it underlies the whole way one approaches science.  The key idea is not to believe in anything.  My whole approach to doing science and one that I would recommend to anybody is never to say, "Aha!  I think this is the answer.  I wonder if it's true."  The key approach is to look at something and say, "Why did that happen?"  And then work it out.  You should do that for everything.  An amazing number of people had no clue what happens when they turn on the light switch because they've never stopped to think, "Why does that happen?"  This happens because it always happens.  That's not the real answer.  It doesn't happen because it's always happened.  So, if you just keep asking yourself "why is it so?" then one day, we'll get to answer these questions.  Now none of us knows the answer to your question.  It's quite possible that you might answer that question one day.  Someone of your generation is more likely to answer that question than any of us today.  But you'll only do it by keep asking, "why is it so?"

Chris -   Please thank our panels this evening, Didier Queloz, Alan Tunacliffe, Gerry Gilmore.  Thanks also to dangerous Dave and Ginny Smith over on the experimental side.  So, this has been a special episode of the Naked Scientists from the Cambridge Science Centre.  We'll be back doing more of this in and New Year.  I hope you've enjoyed yourself.  I'm Chris Smith.  Thank you very much for listening have a wonderful Christmas and goodbye.


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