In Our Time - The Cool Universe

Episode Date: May 6, 2010

The Cool Universe is the name astronomers give to the matter between the stars.These great clouds of dust and gas are not hot enough to be detected by optical telescopes.But over the last few decades, they have increasingly become the focus of infrared telescopy.Astronomers had long encountered dark, apparently starless patches in the night sky. When they discovered that these were actually areas obscured by dust, they found a way to see through these vexing barriers, using infrared telescopes, to the light beyond.However, more recently, the dust itself has become a source of fascination.The picture now being revealed by infrared astronomy is of a universe that is dynamic.In this dynamic universe, matter is recycled - and so the dust and gas of the Cool Universe play a vital role. They are the material from which the stars are created, and into which they finally disintegrate, enriching the reservoir of cool matter from which new stars will eventually be formed. As a result of the new research, we are now beginning to see first-hand the way our planet was formed when the solar system was born.With:Carolin CrawfordMember of the Institute of Astronomy, and Fellow of Emmanuel College, at the University of CambridgePaul MurdinVisiting Professor of Astronomy at Liverpool John Moores University's Astronomy Research InstituteMichael Rowan-RobinsonProfessor of Astrophysics at Imperial College, LondonProducer: Phil Tinline.

This BBC podcast is supported by ads outside the UK. Every Sunday, we talk about the week's tech news on this week in tech. Hi, this is Leo Leport. Inviting you to join me this week with Lisa Schmeiser, Dan Patterson, and Yanko Rekkers. We're going to talk about the new 49 megabyte web page. It's the standard, you know. We'll also talk about Elon Musk. You've got some spleenin to do and the Yassify filter, new from Nvidia.

That's this week on this week in tech. You'll find it at Twitter. or wherever you get your podcasts. Thanks for downloading the In Our Time podcast. For more details about In Our Time and for our terms of use, please go to BBC.co.com.uk forward slash radio 4. I hope you enjoy the program. Hello. Over the last few decades,

astronomers have been using infrared telescopes to make visible the matter between the stars, immense clouds of dust and gas that are not hot enough to be seen with optical equipment. This is the cool universe. Once astronomers thought of this cosmic dust has nothing more than an irritant blocking our view of the bright, important astral bodies.

But more recent research is now revealed how the universe functions as a dynamic system and how this dust and gas play a large and vital role. The size themselves are formed from this cool interstellar matter, and when they eventually disintegrate their elements drift back into these clouds and materials spread across the galaxies. Recent infrared images of these astonishing processes are now allowing us to see firsthand

the means by which our planet was formed when the solar system was born. With me, to discuss the cool universe are Paul Mirdin, visiting Professor Astronomy at Liverpool John Moore's University's Astronomy Research Institute, Michael Rowan Robinson, Professor of Astrophysics at Imperial College London, and Carolyn Crawford, a member of the Institute of Astronomy and a fellow of Emanuel College at the University of Cambridge. Caroline Crawford, can you summarise what astronomers thought of the universe, what it consisted of, and in particular what lay between the South,

on the planets before infrared? Well, astronomers were really concerned with things that were tangible, especially observers. They could only deal with what they saw. So they were interested in characterising the planets, their properties, their orbits, even discovering new asteroids, new planets, trying to work out how stars shone,

even the distribution of stars across the sky, how they structured into the galaxy. But all of this is dictated by what they can see, what they can see with their eye, what they can see through their telescope. And there isn't much thought given to what could lie between the stars, between the planets. They did know there were gas clouds out there.

When did I know that? Well, even in the late 18th century, there was a French astronomer called Charles Messier who was compiling and cataloging a whole host of, they were called nebulae. So there's clouds in space where he was searching for comet. new comets in the sky.

And there were all these little fuzzy blobs in the sky that he would repeatedly observe and confuse with the comets we started compiling a catalogue of them. And some of these were very identifiably gas clouds around stars. So they knew there were gas clouds in space, but the only manifestation they could observe are when they're close to stars and they're lit up and illuminated and made visible.

We talk about an extremely ancient science and practice art of, astronomy you think of the Babylonians and on it goes through. And they're looking, of course, the telescopes are getting more powerful and so on, but still, as it were, the same world out there is being observed all the time until very recently. Yes, it's still the visible light. And in terms of the development of infrared astronomy, that really doesn't start kicking off until perhaps about the mid-19th century. So when it become really clear that the visible, what you could see through telescopes,

that the telescopes we had then. The visible was only part of the equation. Well, the realization that there was radiation beyond the visible really stems back to when the British astronomer Sir William Herschel first discovered infrared radiation. And he did this by splitting sunlight through a prism, so you get all the constituent colours. And he was interested in measuring the temperature of each of these colours.

But to his surprise, he found the biggest increase in temperature was not in one of the colours, but just beyond the red end of the spectrum. So infrared. And that was the infred. And so he made the marvellous deduction that this was a continuation of the visible beyond to a point where eyes couldn't see it

and that there was heat radiation. And there could be other forms of radiation other than that we could see with our eyes. So that was really the first inkling that cosmic objects could give off light in a whole host of different wavelengths. So just got absolutely clear, because that's as it were,

where it started for the purposes of the rest of this discussion. Herschel worked out that something was coming to us from the universe that we could not measure with our eyes. We had to find other ways to measure it. Yes, we had to find other ways to measure it. And this is going to be a key thing as we talk through the development of infrared astronomy is that infrared light, you can detect it as heat radiation.

So Herschel was using a thermometer. By the time we got to the 1850s, there was the first detection of infrared light from the full moon. But to do that, you can't use a thermometer to measure heat radiation from a moon. You have to develop electronic devices to do the detection for you. Michael Rowan Robinson, for Caroline referred to these patches, these dark patches in the sky. Can you tell us how those patches and when those patches were discovered to be dust and what was thought of the dust initially?

Yes, well, it took a long time. time. I mean, it wasn't really till 1930 that people first that, in fact, it was the American astronomer Robert Trumpler, who realized that there was something between the stars absorbing the light from them. And he did this, and it was quite an indirect

discovery. He was actually studying clusters of stars. And he was making a catalogue of 300 clusters of stars. And he was estimating the distance of them from the brightness of the stars and making this catalog and working out the size of the clusters and so on. And then he realized that this didn't

make sense because when he looked at the more distant clusters, they were all bigger. And he thought, well, no, we think all these clusters are the same wherever they occur in the galaxy. So something must be wrong here. And he realized that the explanation was that there is something between us in these distant clusters that's absorbing their light, making the stars look fainter. And so he was incorrectly, assuming they were further away, and therefore that the clusters were bit intrinsically larger than the nearby

clusters. So he realised there was this absorbing medium in our galaxy, cutting out the light, and he also realized, at the same time, that this medium, or whatever it was, it didn't really speculate on

exactly the nature of it, but he did realize that it also affected the colours of the stars in the sense that there was more absorption in blue light than there was in red light. But they were seeing this stuff was originally, even in 1930s seen as a barrier? Yes, so at that time, infrared astronomy really hadn't got very far. It had, as Caroline said it, the moon was detected by, perhaps his smithing in the mid-19th century. And then it wasn't really until about 1900 that the first stars were detected.

The problem was the detectors. As Karen said, the development of detectors was a very slow business, getting them good enough to detect the very faint radiation. So when did people stop thinking this stuff is getting in the way? It's an impediment. To start thinking this stuff in itself is very interesting, we're about to find a way to examine it. Well, that really is 1960s, I would say,

that the first attempts were made to look for infrared radiation and see what it might be telling us. So Jerry Noigabar and Bob Layton set out in about 1965 to make a survey of the whole sky at a wavelength of about 2 microns, so in the near-infrared wavelengths, And...

They were told it was always a time. That's right. Yes. The optical astronomer said, why do you want to do this? I mean, all you do is detect the stars and, you know, there's an immense labor just to work out the brightness of those stars.

Anyway, they persisted, and they did find lots of stars, of course. I mean, the majority of the objects in their catalogue are just stars where you're seeing the infrared light beyond the visible part. But there were lots of interesting objects. And the interesting objects, the things that were brighter than expected in the infrared.

And the first kind of object that began to be, to emerge from this survey, were dying stars. So essentially the stars like the sun, really, mass similar to the sun, but further on, they've stopped burning hydrogen in the middle, they've stopped fusing hydrogen in the middle, and they've become red giant stars. and as they do so they blow out clouds of dust before we go on I ask Paul Mergent and develop it

can you just tell us what what sort of instruments they were using at this time so how were they able to see what other people had not seen yeah well the telescope was really small it was about 60 centimetres across and they made it themselves by

rotating a sort of parabolic disk with epoxy resin on it to make the shape of the mirror. So it was a very simple telescope, but it was really the detectors. And the key detector was the detector advance was the lead sulphide cell. So this is basically crystal of lead sulphide.

And when infrared radiation falls on it, when heat falls on it, the resistance of it changes slightly. So you can measure this electrically. So essentially you measure the heat falling on this crystal because the electrical resistance of the crystal changes slightly. So the heat falling on the crystal gives you the new map of the universe?

Essentially, yes. Paul Morden, how fundamentally different does the universe, or did the universe, look after that and has it continued to look since further and further developments in this kind of examination? Well, let's talk about an example. If you go out into the evening sky this evening and it's clear, then you'll see the constellation of Orion setting in the west.

And as Carolyn said, the optical view of that constellation is the fundamental view historically. And if you look at the central star in the sword of Orion, you'll see a little fuzzy patch around it. You can see it with the naked eye, see it much better with binoculars. and that is the Orion Nebula. So the optical view of Orion is an array of stars with this nebula surrounding this one star. And in fact, when you peer closely at that star,

you can see that it's four. Now, if you take an infrared view of Orion, the situation is completely transformed because you see everything which is between the stars and in the direction of Orion, there is a lot between the stars. it's the area of the galaxy where there's the nearest large giant cloud of this material. So the whole constellation is completely luminous with infrared radiation.

And the Orion Nebula, it turns out, is simply a little dimple on the surface, on the nearby surface of this big cloud. You think of an apple that somebody's taken a small bite from. the small bite where the white flesh of the apple shows through, that's the Orion Nebula. And what you don't see with your eyes is this vast cloud behind it. The four stars that illuminate the nebula are the four stars that happen to protrude through the surface, where that's a little sculptor bit, sculpted bit has been taken out.

But if you look with infrared, behind that, there are literally millions, perhaps tens of millions of stars. All of them recently formed. all of them brand new stars, many of them still... Brand new to us. Well, brand new to us and brand new. I mean, they are literally formed yesterday in astronomical terms, perhaps only a few million years ago, a few hundred thousand years ago.

And they still are going through their birth pangs. They still, they haven't reached the stability that, thank goodness, our own son has reached because it keeps us in stable conditions. They're still dynamic, evolving. objects, as it were, stars in their birth pangs, completely new kinds of objects. So the whole view of the constellation is conceptually different from the view you get

when you stand in your garden this evening and look at the constellation. And what does that lead you to think might be a consequence of this? Well, I think it focuses attention on the potentiality for the whole universe, the whole galaxy, system of stars and gas and dust and now the things

between the stars. It focuses attention on the possibility that that's all the dynamic process. The universe in ancient times was a very static place. The time scale for things to change much longer than human lifetime. So during your lifetime as you observe the stars, you see the same thing repetitively time after time.

Different views of the same object as the seasons progress, but essentially the constellations don't change their shape, the stars don't change their relative brightness, certainly not noticeably and certainly not by much. But the modern view of the universe, the modern view of the systems of the stars, is that everything is in dynamic equilibrium, is changing from one thing to another,

it's progressing from a start to a finish. It's a much more dynamic place with aging and mutability and time as a fundamental coordinate, a fundamental dimension of what it is we see. And as I understand it, the best way to see this is to hoist telescopes outside, up in space,

because our atmosphere interferes with the messages coming in, the radiation is coming in. The problem for infrared astronomers who live on the Earth is that the Earth is part of the cool universe. I mean, it's at the temperature that it's at, you know, about 280 and 300 or so degrees absolute about them. well, the temperature, the room temperature. And so the earth and everything in it is radiating not just some infrared,

but copious amounts of infrared, that completely, will completely, usually completely swamp any celestial signal. The sun, if you pass, as Herschel did, if you pass it's light through a prism, and you measure it with a thermometer. Well, that's okay. You can measure the infrared radiation from the sun. then it takes an enormous length of time for the technology to develop so you can detect the next brightest thing in the sky and the moon

and then even longer to detect anything which is of fundamental significance to infrared astronomy. So being on the earth making instruments using telescopes that are sensitive to infrared radiation, you're simply dazzled unless you take special technological care by all of the infrared radiation that's coming from around you. If you go to an infrared telescope, a telescope that's used for infrared astronomy, you'll find it a strange place full of refrigerators and steaming carbon dioxide fumes and from dry ice and there are liquid helium tanks and there's piping and there's frost forming on the cold piping and so on.

It's a strange Frankenstein laboratory sort of looking place. as people have put the technology into cooling down anything that might shine infrared radiation into the detectors. But the fundamental limitation that you've got on the earth is that you're on the earth, you're looking up through the atmosphere and you're looking through warm air. So the warm air itself is a hindrance. And the only way out of that is to take your detector

and your telescope and your system on a satellite into space. Which they are doing. and have done and are doing frequently with more and more technological successes, I understand it, but we'll maybe come back to that current. So the dust and gas is out there. Can you tell us what conclusions were arriving at as to its importance?

Why did it, when it seems to be just a bother and a nuisance and getting in the way and people said we must examine this because something is going on here, what did they find that was going on here that was worth examine? Well, I just want to pick up Paul's point about temperature and radiation, because this is key to why infrared astronomy is so important. And you have to think of any cosmic object radiates light, but the waveband that it radiates predominantly and depends on its temperature.

So if you're at something that's at tens of thousands of degrees, like stars, like galaxies made of stars, you radiate in the optical. But if you have matter that's cold, that's maybe tens hundreds of degrees above absolute zero, and absolute zero is minus 273 degrees C, they are too cold to give off optical light, and they radiate in the infrared. So cooler objects give off redder light. And this is key because with the optical astronomy, we just saw the stars, and we had no vision of what lay between the stars. With the infrared astronomy, you begin to.

to see this whole new component to our galaxy, the cold matter and the dust particles that lie out there between the stars. And this is fundamentally important because this is the matter that the stars themselves and any planets and obviously any

life forms on those planets are formed from. So it's a completion of the picture from just being the stars to being a matter between the stars and that symbiosis that Paul alluded to between the stars and their environment. So what To come back to the question,

what was important about what was being called dust or stuff getting in the way, spludges you called them earlier on? What was found to be important about that which had been ignored or thought of as a nuisance? Well, not understood. First of all, how widespread it was. It's concentrated within the plane of our galaxy. Our galaxy is a disk shape.

And within that disk, there are huge clouds of diffuse gas. Now, some of them are... What do you mean by here? Well, things that can be light years in diameter. Which is? A light year is 9.5 million million kilometers. So you get to these meaningless numbers we always deal with in astronomy. But within the plane of our galaxy, you have clouds which are colder than the environments.

And they're invisible to optical eyes. Perhaps they're mainly composed of neutral hydrogen atoms. And maybe we just detect them up in radio. because they are very cold. But within these, you have even denser pockets where you have gas mixed with particles of what we call dust. And these are the opaque clouds

that Michael was talking about, that block that, if you look in the optical, they block the light of the background stars. But they, because they, that light from the background stars is absorbed by the dust in these clouds, they become luminous in the infrared and they begin to glow.

And you begin to study these stars. And the key thing is that this is where star formation occurs in the cause of these clouds. Can we take that on then, Michael O'Romanston? So this is far from being a nuisance, they turn to be crucial. This dust, let's keep calling it dust until you tell me a better word, turns out to be crucial.

Yeah. Well, I mean, one of the crucial things about interstellar dust is it's where it's a sort of reservoir of the elements that we're made of and that stars and planets, well, planets are mainly, a planet like the Earth is made of, mainly of heavy elements like carbon, nitrogen, silicon, iron and so on. The stars are mainly made of hydrogen. Now, the heavier elements.

And we too. And we too are a mixture of all these same elements. Absolutely, the same elements. And, well, we'll later talk about this cycle of the elements through the interstellar medium. But essentially, the elements like carbon, nitrogen and oxygen are made in stars like the sun or a little bit massive. They then are convective to the surface of the stars, blown off in these winds that I mentioned earlier that Noigabar found in his survey. and so they then, as it were, pollute the interstellar gas with these heavy elements. As soon as they get cool enough, as soon as this material gets cool enough, it forms into grains of dust.

And so, for example, a carbon ends up in little graphite or amorphous carbon grains. We have little specks of soot, as it were, out there in the, so that some of the grains of soot. Other material like silicon and iron is made in much more. massive stars, like 10, 20 times the mass of the sun. When those stars die, they blow up as a supernova. So a huge explosion blows up the whole outer part of the star. And again, that material floats around. When it's cool enough, it forms together to make silicate. So basically sand. So we have sand and soot is really what the main ingredients of interstellar space. And so that's, that's as it were, the reservoir.

are these elements, which later on are going to accumulate into new stars, which have got a bit more of this heavy stuff, and also planets. Paul Murdin, can we take this sand and sort which let's say brings it down to Earth

really, and how those develop into new planets, how that cycling, can we go into the way that cycling happens? Well, it happens as the interstellar material, as the as the dust and the gas in interstellar space forms new stars

and the planets are a byproduct of the formation of a star. In the galaxy there are great big clouds of hydrogen left over from the Big Bang and possibly hydrogen that has never been part of stars. And this hydrogen gets polluted by previous generations of stars.

which have exploded and sent dust into them, or stars that have leaked into space so that their bodies leak into space and grains of dust are put into the hydrogen clouds. Something happens. Maybe the cloud gets too big, maybe there's another passing cloud that disturbs it, maybe there's a supernova nearby that compresses a local area,

or something happens. And a lump forms inside one of these interstellar hydrogen clouds. And if the lump is large enough and compact enough, then the force of gravity of that lump takes over the control of the process from then on. The cloud collapses, gets smaller and smaller and smaller. And that process makes a new star. And in the process of making the new star, some of the material gets spun off into a disk around the stone,

and condenses further to make the planets, a planetary system. And this is really where the infrared is so important, because just as Paul is describing, this happens in the center of these clouds, and gravitational collapse happens preferentially where things are coldest and densest. And so first of all, it's happening really obscure parts that are shielded from our visible eyes.

So to see actually into the clouds, to see this process taking place, the infrared light. But also as that cloud collapses, forms the proto-star at the core, it's becoming more opaque, is blocking out any light from the nascent star at the core. So all this process of the actual star formation from the cloud, let alone the planets around it, are hidden from our optical eyes. And we can only begin to probe that with infrared astronomy, begin to observe that process, not just of the actual formation. of the star from what we think

is a sort of disc of material around it but also the planets within that disk. Yes, I wanted to bring up another aspect of the need to go into space and that is that a lot of the radiation doesn't get through the atmosphere. So basically

the need for the instruments themselves are going to space. Yeah, the need for us to get our telescopes into space is because it's partly what Paul said that of course, you know, the atmosphere is so bright, the earth is so bright. But also, we only get a little bit of the radiation. So there are a few little windows of wavelength, near infrared wavelengths.

There are a few windows at much longer wavelengths in the sub-millimeter. And in between, none of it gets through at all. So it was only when we got into space that we could really see this whole cool universe. So when Paul talks about Orion shining out, is these clouds of gas actually shining at us. We first saw this when we put the infrared astronomical satellite, IRAS, into space in 1983. So that was the first moment. We actually saw this dust shining at us. Now, another thing that we saw the first time was debris disks around stars. So the first one that was seen was a very bright star Vega, which is

overhead in the summer. And we saw around this a disk of dust and material almost certainly also planets within it. And this was the first glimpse of a planetary system

a probable planetary system around another star. Up till then we knew about our planetary system of course. We thought there were probably planets around other stars. We had no direct evidence. It's the first moment we saw a planet disc. Caronleyn, can you explain how these phenomena led to the creation of solar system here, and especially with reference to the rocky planets nearer the sun and the gaseous planets further away from sun?

Well, if any, we knew really the answer to that question. I mean, we have good guesses how it works, and again, infrared astronomy over the last couple of decades has been key to studying these debris disks that Michael's mentioned, because when we left Starformation from what Paul described, you have the protist star developing within this opaque cocoon of material which later flattens out and develops into planets. But the process from, you know,

this cocoon turning into a planetary system is complicated and it's not something we necessarily understand. We can look at the debris disks and sometimes... Can you give us some idea of the time as you're going through this? Well, time involved, how long would it take? Well, for the cocoon to perhaps collapse down to a disc,

I mean, again, it's quick in astronomical terms. We're still talking a few million years. It's something that's quite transient, but we see it in enough stars that we can begin to study the process. And you can look at the debris disks and you look for unevenness in them. Maybe they're a bit lumpy. Maybe that suggests as a giant planet forming within that disk.

You can perhaps begin to see the stages from when it's just this cocoon to the planet's beginning to distribute within the disk. The problem is that the area we can see best is far out in the disk, which in terms of our own solar system scale, would be out beyond Neptune. That's where we can see the light most clearly, where it's not going to drowned out by the light of the star. Could we just concentrate on our solar system? Just make it a little local.

Well, I was going to come on to that, because the kind of systems we can study in terms of other platforms, around other stars that we know about, they don't look like our solar system. So we have to dot the lines between the debris disks to the planets we see around other stars. Now, we thought we understood the solar system, four rocky planets close into the sun, and then the gas giants with the much more gaseous volatile compounds formed further out in the solar system where this cocoon, this solar nebula is going to be colder regions. what we see in the debris disk

is we see these giant planets forming far out when we look around planetary systems observed around at the stars at the other end of the scale we see these giant planets in close to the star so there must be a process where they migrate perhaps in Michael I just wonder I mean I think the key step in going from a disk of gas and small dust grains

towards planets is the formation of what things that are called planetesimals now these are These are about 100 kilometres in size, say. And so it takes about a million years for dust to aggregate together, dust and gas to aggregate together into these lumps. And it's from those that the planets are built. Now we see, in our solar system, we see these planets, decimals, still around, the ones that didn't make it to a planet.

So in the asteroid belt between Mars and Jupiter, there are millions of these lumps of stuff that could have made a planet. if things had been more favourable. Further out, in the Kuiper Belt, we see more asteroids, millions, if not billions of asteroids. And even further out, we see the comets, the Oort cloud of comets, which occasionally come in. These are all, these lumps, really,

these planetesinals, probably going back to when the solar system was formed. So that's the key step in this process. Paul, Paul Modder, now we're getting a new sense of the history of the universe from this infrared investigation? Well, I think these cyclic processes in which stars are formed

have been going on from year dot to now. And if you could map the understanding that we're developing about the formation of stars and the formation of planetary systems, if you could map that into successive stages in the history of the universe, then you would understand the development of the components of all the universe.

And you'd be able to see, first of all, the cyclic nature of it, the way in which interstellar material and diffuse material that lies between the stars condenses into stars and then is returned back into space and then condenses again and forms new generations of stars, a continual repetitive cycle, mapped onto a progression. from the beginning to now,

as more and more of the material of the universe has been recycled through stars, cycled again and again and again, and progressively enriched in these heavy elements. Progressively, as time goes on in the universe, we get more and more of the sorts of elements that are favourable to the formation of planets and the formation of people.

So you In the notes I read from you said that in our little finger there's carbon that has been recycled So is there sort of big bang stuff in our little finger There's stuff from that far back Are we just Are we at some certain stage

Probably a millionth of way along a recycling Going to end up with some decent life around the place Sometime or other The Big Bang didn't make very much When you have a No I know it's talking about the Bion Helium Balloon Charles Hylian Balloon has some

Big Bang stuff. No. All right. So take an element of carbon in our finger. That piece of carbon was made inside a star billions of years ago,

blown out into the interstellar medium, cycled around, eventually pulled together to make a new star. Perhaps it's been through this several times. Eventually it finds itself in one of these planetesals in the solar system.

It ends up in the Earth. and eventually somehow through all these biological processes, it ends up in our little finger. So there's a wonderful cycle of the elements, from the cores of the stars, into the interstellar medium, into the new stars and planets, and so on. Round and round it goes. Indeed, the process of this material, interplanetary material,

all this dust, raining down on the earth, that hasn't finished. It's not something that took place historically in astronomically long time ago times. It's still happening now. There are still millions of tons of dusty material from space that rain down on the earth every year. So not only was the great wadges of it that came down onto the earth at the time the Earth was formed because there was lots of lots of dust in the solar system at that point and the Earth was building up very quickly. But it's still happening now. So the The carrots that you grow in your vegetable patch are growing in this interstellar dust, in this interplanetary dust, which is still raining down on us. I mean, I think one of the really interesting things recently has been the discovery of a third ingredient

after sand and soot, and that is the exhaust from the soot in the exhaust pipe of a car. So these are polysounding. aromatic hydrocarbons. So these are quite complex molecules, benzene-like structure. And these have been found in intercellar space. They have very characteristic wavelengths pattern that we've recognised over the years. Now these things are big molecules of hundreds of atoms probably. And recently, Louis Alamendola has been doing experiments in the laboratory and he's synthesized this stuff basically.

He synthesized something very like the interstellar PAHs, as they called. And he found that if he subjected this stuff to ultraviolet light, dissolved it in water, some sort of tubules were left behind, very like both chemically and structurally, rather like the membranes of cells. And so there's a possibility that the first, steps towards life in terms of providing the structures that are needed for life to grow could happen in interstellar clouds and rain down on the earth.

Can I move it on now? Because I really want to have something about our solar system before we clock off. Is there any sense in which, from what has been newly discovered, let's say over the last 70 years, that our solar system is unique? Carolyn, can I ask you to address that? we haven't yet found one like our solar system it may well not be unique we certainly think there's such a plethora of solar systems out there

one is going to resemble ours the difference is that these protoplanetary disks that we've found that are forming planetary systems the ones we tend to have studied best tend to be in quite harsh environments quite close to bright young stars and you have intense radiation you have intense sort of pressure of that

that starlight and winds from the stars and they strip off the outer layers of these disks and potentially remove all the stuff that in our solar system has gone on to form maybe this coiper belt of frozen comets and dwarf planets

and perhaps any solar system that forms from then will only have, will be fairly compact and not as diffuse and spread out as our own solar system. But that's just speculation. We're still at the process where we're discovering these other debris disks.

and these protoplanetary disks and just trying to characterize how different they might be in any solar systems that might eventually form from them from our own. We're always intrigued by whether or not we're unique. I mean, it's a continuation

of the human vanity and conceits and so people have started writing about themselves, but still it is an interesting question. Can you develop that at all for what's Caroline said? Well, I think that the Earth is rather rare. I mean, certainly we know now that there are many, many stars, a large fraction of the stars that have these debris

disks around them and we know of, I mean literally hundreds. I think the number now is four or five hundred of planetary systems outside of our own. As Caroline says, they are all different from our Earth, but they would be because of the nature of the technology and the timescales and so on that we've been able to study those. The first such system really was only discovered in 1995, so there hasn't been time to find a solar system. But I'm struck by the fact that all of these planetary systems are very dynamic places with Jupiter-sized bodies cascading through,

bodies that would sweep up Earths. And there are many, many fluky things about the architecture of our solar system. I mean, the Earth, for example, has a moon, which is of comparable size, and that is thought to be due to the collision in the past of two large planetesimals that collided one with another and made a double planet. And the effect of that double planet is to stabilize the Earth in its spin and to make a very stable platform in which things are sort of constant for literally billions of years

over the time scales for evolution. So you have a fluky thing which happened early on in the history of the solar system a particular kind of collision that produced a particular kind of double planet in exactly the right place to give something which is earth-like. And there are other examples of similar sorts of things.

And I'm struck by the fact that the particular way in which our solar system is constructed the architecture of it, as I say, is the result of what one could imagine are rare and fluky circumstances. So I think that one of the reasons why we haven't seen any aliens on Earth is because the nearest place where life might have developed in a solar system like ours

is a very, very long way away because this particular architecture is rare. and inter-solar beings haven't developed the technology to travel such large distances. I think that in our time might not just be unique in England. It might not just be unique on the Earth. It might be unique in the galaxy. Well, I'm not sure I quite agree that the solar system is, that there aren't going to be other solar systems.

I mean, it is very much a selection effect that we couldn't have, It's very hard to detect planets as small as the Earth so far. I mean, this is the exciting thing of the next decade that new missions are planned, new telescopes are planned, which will be directed at finding planets like the Earth. And that is something we have to look forward to. I'm going to bring the whole conversation to a crashing pathetic close by saying, watch that space.

Sorry about that. Thank you very much, Carolyn Crawford, Michael Rowan, Robinson, and Paul Mirdin. Next week, we will be talking about William James, the varieties of religious experience, came from lectures in 1901, 36 reprints, influence Huxley and Young, and so on. Thank you very much for listening.

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