The Moon (Archive Episode)

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Speaker 8 Now, to mark the end of his 27 years this month of presenting In Our Time, we have Melvin Bragg to introduce the first in a series of his most cherished episodes.

Speaker 4 One of the pleasures of In Our Time for me is that it's become the university of the airwaves.

Speaker 4 Each week I and countless listeners have been marveling as three three brilliant academics share their expertise on history, culture, philosophy, science and religion, no subject too great or small.

Speaker 4 We've made almost 1100 episodes, each a favourite, but we can only have a few for this occasion. So let's start with this one from 2011 on the moon, an object so familiar and so full of mystery.

Speaker 4 And we have such wonderful guests. In this episode, for example, sitting opposite me in the studio one Thursday morning was the man who co-discovered the first black hole.

Speaker 7 Hello, on November 30th, 1609, Galileo Galileo pointed his telescope at the moon. He was astonished by what he saw.

Speaker 7 I found the surface of the moon, he wrote, not to be smooth, even, and perfectly spherical, but uneven, rough, and crowded with depressions and bulges.

Speaker 7 And it's like the face of the earth itself, which is marked here and there with chains of mountains and depths of valleys. Galileo was the first human being to report these features in such detail.

Speaker 7 But the moon with its power over time and tides has fascinated mankind for millennia.

Speaker 7 Locked in an orbit a quarter of a million miles away, our closest neighbor in the solar system and our only natural satellite, the moon exerts a powerful influence on life on Earth.

Speaker 7 More than 70 spacecraft have been sent to the moon and although we've now walked on its surface, there are still many things about this four and a half billion year old hunk of rock that remain a mystery.

Speaker 7 With me to discuss the moon are Paul Murdin, visiting professor of astronomy at Liverpool John Moores University.

Speaker 7 Caroline Crawford, Gresham Professor of Astronomy and Outreach Officer at the Institute of Astronomy at the University of Cambridge, and Ian Crawford, Reader in Planetary Science and Astrobiology at Birkbeck University of London.

Speaker 7 Paul Merdin, what is the Moon?

Speaker 3 You described it well in your introduction. It's a satellite, it's the satellite of the Earth.
It goes around the Earth just as the Earth goes around the Sun.

Speaker 3 Actually,

Speaker 3 that vocabulary puts the Moon in a kind of a subordinate position.

Speaker 3 And it might not really be like that.

Speaker 3 The Moon is smaller than the Earth, but it's a quarter of the size of the Earth, and so it's comparable to the Earth.

Speaker 3 And you could say that the Earth and the Moon form a twin planet that goes around the Sun.

Speaker 3 The orbit of the Moon has a radius of about 350,000 kilometers, a quarter of a million miles, pretty much circular.

Speaker 3 And the Moon goes around the Earth once every month, hence the name of the unit of time, the month, associated with the Moon.

Speaker 3 It's spherical, pretty much, slightly flattened at the poles. It's a bit pointy, like a pear,

Speaker 3 and it points towards the Earth.

Speaker 3 The lump on the side points towards the Earth. And the Earth has a kind of grip on that point.

Speaker 3 And so the Moon always keeps the same face towards it. So when you look at the Moon, you can always see exactly the same arrangement of grey and bright patches.

Speaker 7 What do we know of its composition and its climate?

Speaker 3 Its climate is simple to describe because it doesn't have one. It's airless.

Speaker 3 It's either very hot when it's in the sunlight or it's very cold when it's... Very being watered.

Speaker 3 Can't remember.

Speaker 7 Very, I think, is 180. I can't remember.

Speaker 3 Its composition, well, its density is very much like the density of the rocks on the crust of the earth. And that's pretty much what it's made of.

Speaker 3 It's made of the ordinary kind of minerals that you find in the crust of the earth, things like basalt.

Speaker 7 Since the prehistoric times, the moon seems to have had an influence on human culture.

Speaker 7 Can you tell us about the early evidence of men and women being intrigued by the moon and using it for the beginning, it would seem, of intellectual thought?

Speaker 3 The most noticeable thing that you can see about the moon with the naked eye is the fact that it's got phases.

Speaker 3 The bright part, the bit that's lit up by the sun, changes in aspect relative to the earth, so that when the moon is in front of the sun in the same direction as the sun, it's the back of the moon that's illuminated and you see the dark face of the moon.

Speaker 3 When the moon is behind the earth, away from the sun, you can see the whole hemisphere, and so it's full.

Speaker 3 And so you see the progression of phases from dark to crescent to half moon to full moon and then back to new moon again. And that's a pretty obvious thing to notice.

Speaker 3 And mankind must have seen that right from the very earliest times. And in fact, the earliest observations of any astronomical phenomena that now still exist are observations of the phase of the moon.

Speaker 3 There are two fragments of bone that have been dug up in archaeological circumstances. One, a piece from some caves near Dodogne,

Speaker 3 and

Speaker 3 one a piece of bone that was the handle of a knife that was found in Africa.

Speaker 3 And these date from about 20,000 years ago, and each of them has got scratches or marks on it, which run in cycles of 29 diagrams of the phases of the moon.

Speaker 3 in groups of 29 running over about three months. So 20,000 years ago there were people who were making notes of the phases of the moon for some reason.

Speaker 3 In the case of the bone handle, it might have been a hunter that was off on a journey,

Speaker 3 wanted to find his way back home in time, or it might have been a woman who was keeping track of her menstrual cycle and her fertility for some reason.

Speaker 7 So Caroline Crawford, we could characterise this as the beginning, the first evidence, or early evidence of intellectual activity among people who began us.

Speaker 10 Yes, and certainly the... the importance of the moon for the timekeeping continues in terms of

Speaker 10 longer than a month or so, looking at the extreme of when the moon rises and the moon sets in the earth.

Speaker 10 So by the time you get to prehistoric times, you have 7000-3000 BC, you have structures like Stonehenge, which give you permanent observation points to monitor the moon rise and the moon set.

Speaker 10 And as Paul says, you start off with the idea of a lunar cycle establishing a month, which eventually gets divorced from the calendar month that we use nowadays.

Speaker 10 But nonetheless, we've still got this powerful pull about the importance of the moon for the activities that we carry out.

Speaker 7 It's taken a lot of cultural associations. There's a harvest moon, the blue moon, the hunter's moon.
Could you develop some of those?

Speaker 10 Yes certainly because again if we go back several centuries having a full moon at night is crucially important. It illuminates if you're if you're travelling it makes your travelling safe.

Speaker 10 If you're a farmer If you have a full moon, it's enormously helpful when you're gathering in the crops and particularly you have this phenomenon of what we call the harvest moon that happens around the September equinox because what happens is the moon rises about an average 50 minutes later each day.

Speaker 10 Around the September equinox it's only rising like half an hour later each day.

Speaker 10 When the sun sets the full moon rises and you get this period of a few days in a row where as the sun sets you get a full moon rising very soon afterwards allowing the workers in the field to continue working bringing the crops.

Speaker 10 So that's your harvest moon and there's a similar thing a a month later with the hunter's moon, where the moon can again help hunting late into the night around the period of the full moon.

Speaker 10 So it was illuminating activities. You mentioned blue moon.
I mean, that again, that arises from observations of the moon and again this period of behaviour.

Speaker 10 And the way we look at it now, it's this occasional occurrence when you get two full moons in one month. So if we say once in a blue moon, it's something that doesn't happen very often.
And

Speaker 10 you have the moon going around its lunar cycle every 29 days and you get 12 of those in a year but there are 11 days left over. So the 12 lunar cycles don't fit into the 365 days of our year.

Speaker 10 So after about two and a half years you've accumulated enough days that you can pack in an extra lunar cycle and every so often you get one month with a full moon at the beginning and the end of the month and that second moon is now the blue moon.

Speaker 10 So again this idea of once in a blue moon again is a very rare occurrence.

Speaker 7 I was just thinking rather gentler pursuits than you were than hunting, and because there was a great fashion for moon walking.

Speaker 7 And in the Lake District at the time of Wordsworth, they would go out and read by a bright moon, read their poetry.

Speaker 7 I'm placed a blind

Speaker 7 to see if you could read by a full moon. You can very well, even me with my eyes, aren't so good.
So, there's reading by a full moon as well.

Speaker 10 Okay, well, that's really another example of just again how important the full moon was to our predecessors.

Speaker 7 Can you tell us how we know we all know the tides are dictated by the moon, but can you tell us how that works and how that deeply affects our planet?

Speaker 10 Well, yes, the tide, we've long since known that the tides are affected by the phase of the moon, and it's to do with the gravitational pull of the moon.

Speaker 10 And it's not just the fact that the moon pulls on the waters of the earth, but it pulls differently on the waters on the near side of the earth, near side to the moon, than on the far side.

Speaker 10 So, for example, when you think of the Moon's gravity, you have to realize that it drops off very sharply with distance from the Moon.

Speaker 10 So, if you look at the water on the near side of the Moon, so on the near side, the side of the Earth nearest to the Moon, is getting pulled to the Moon more strongly than the Earth underneath it.

Speaker 10 So, it rises up to form a bulge of water that then basically follows the Moon round in its orbit around the Earth. But meanwhile, the Earth is rotating under it.

Speaker 10 So, that tide, that bulge, appears to travel across the surface of the earth it's being pulled around by the moon but of course there are two tides in every day and you have an equal and opposite high tide because not only is the near side of the ocean being pulled towards the moon you also have an effect that on the far side of the earth away from the moon the earth is being pulled to the moon more strongly than the water on that side and you you have the water is left behind to create a second high bulge within the oceans.

Speaker 7 So as Paul said at the beginning of the programme, they do seem to be a system in themselves,

Speaker 7 a twin system. Without the Moon making the tides, making the climate, the sort of life that we know would probably not exist on Earth.

Speaker 10 Certainly it's been very important for the development of the Earth and

Speaker 10 these tides are a crucial part of the pattern of the Earth and the climate, as you say.

Speaker 7 Ian Crawford, how is the Moon influenced by the Earth?

Speaker 11 Well, it's reciprocally, really, because,

Speaker 11 as Paul said, the Earth-Moon system really forms a double planet. So just as the Moon raises tides on the Earth, the Earth raises tides on the Moon, except they're about 20 times stronger.

Speaker 11 So the consequence of this is that

Speaker 11 the Moon has become tidally locked to the Earth, so it can never

Speaker 11 freely rotate. It means that, as Paul described, the Moon is having slightly pear-shaped geometry.
Now, part of this is the tide raised in the Moon by the Earth's gravity.

Speaker 11 And the Moon has been trying to rotate underneath its tides, as the Earth does under its water tides.

Speaker 7 And we think, sorry, I have have to interrupt, I'm just trying to get it clear. We associate tides with water, and yet we don't see water on the moon.

Speaker 7 So, when you're talking about tides on the moon, what are we talking about?

Speaker 11 That's right. So, these are the body tides.
These are the tides raised in the crust and mantle of the planet.

Speaker 7 Which actually swells and falls?

Speaker 11 Yes, of course, a far smaller amount than does water, because rock is much more viscous.

Speaker 11 But it's enough for the Earth's gravity to get a lock on the Moon, such that the Moon is forced to rotate once each time that it orbits the Earth. And so, from our point of view, we only see

Speaker 11 the same face on it. But

Speaker 11 the tidal locking of the Moon, so we see just one face, is perhaps the most obvious consequence of

Speaker 11 the Earth's influence on the Moon. But there's another side to this coin,

Speaker 11 and that is that this tidal interaction between Earth and Moon is causing the Moon to recede.

Speaker 11 So it's currently drifting away from us at about four centimetres per year as the Earth loses its rotational energy and cans it through gravity to the orbital energy of the moon.

Speaker 11 So the moon is receding and this will actually continue until both planets become locked so that the earth rotates once a month, the moon rotates once a month, and the earth keeps the same face pointing to the moon and the moon goes and but the month at that stage will be about 50 days long and it won't happen for many, many, many, probably tens of thousands of millions of years.

Speaker 11 But eventually when the moon when the earth is tidally locked to the moon,

Speaker 11 this interaction will cease and they'll both just keep their same faces to each other.

Speaker 7 What'll it be like then then? Will there be tides and stuff here?

Speaker 11 Still there's a well at that point there won't be

Speaker 11 because the two bodies will have stopped rotating with respect to each other. But it will happen

Speaker 11 no one will live to see it. The sun will have become a red giant star before.

Speaker 7 But it will have been blown up before that happens.

Speaker 11 I think that is the same thing.

Speaker 7 Oh, that's a relief.

Speaker 7 What can you tell us, Ingram, about the composition of the Moon and how we know its composition?

Speaker 11 Yes, yes, I can. So the Moon is a small rocky planet like the other planets in the inner solar system, Mercury, Venus, Earth, and Mars.

Speaker 11 And I think, although the Moon is a natural satellite of the Earth, and so

Speaker 11 strictly is a Moon, from a geological perspective, it's best seen as a small rocky planet, like the other planets in the inner solar system.

Speaker 11 Now, we know about its composition really from three main lines of evidence.

Speaker 11 The first is the observation of the surface of the near side, which we can see from the Earth, initially with telescopes and then more recently with spacecraft, which have enabled us to determine the make observations of the far side also.

Speaker 11 Then there's the density of the moon that Paul's alluded to, which is very important, the fact that it's got a density similar to silicate rocks, mantle, and crustal rocks on the Earth.

Speaker 11 And then finally, there's the tremendous geochemical evidence that's been produced by, or has been learned, from the studying the Apollo samples of the moon brought back 40 years ago.

Speaker 7 What does that tell us? You emphasise tremendous injuries. life.

Speaker 11 Well, I think the scientific legacy of the Apollo programme can't really be overestimated and certainly

Speaker 11 our understanding of

Speaker 11 the composition of the moon.

Speaker 11 Just backtrack a little bit, just to put this in context. If you look at the moon from the earth, and everyone should do so, it's very prominent tonight.

Speaker 11 There'll be a near first quarter moon this evening, and everyone should look at it. And if you look at it, you'll see there are the surface is not a homogeneous surface.

Speaker 11 There are light bits and dark bits. And dark bits are the so-called lunar seas, lunar mare,

Speaker 11 and the bright bits are the so-called lunar highlands. Now what we've learnt from examining the Apollo material is the precise mineralogical composition of these.

Speaker 11 So Paul mentioned basalt, but it but in fact basalt is a is a volcanic rock and the lunar mare, the lunar seas, are indeed basaltic volcanic rock.

Speaker 11 But the bright areas of the moon, the so-called lunar highlands, are made of another rock type.

Speaker 11 It's called an orthrocyte and it's made principally of just a single mineral, Plagioclase feldspar, which is a light-coloured rock and it gives the lunar highlands its bright, its bright colour.

Speaker 11 So I think from a top-level point of view, from lunar geology, it's studying the lunar samples have enabled us to see the moon as a geological body

Speaker 11 and to understand its geology in detail, its mineralogy in quite great detail now.

Speaker 11 So

Speaker 11 those are the three main lines of evidence anyway, but I think it is the Apollo samples that primarily enable us to answer definitively the question: what is the moon made of?

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Speaker 7 Paul Merden, can I come back to you? There have been a number of different theories about how the moon was first formed.

Speaker 7 Can you run through one or two of the earlier ones and settle on the current one and we'll explore that?

Speaker 3 Well, one idea which was prevalent at

Speaker 3 120 odd years ago was that the moon and the earth earth split apart, the so-called fission origin of the moon.

Speaker 3 If you look at a geographical globe, you can see that the hemisphere of the Earth where the Pacific Ocean now is is almost empty of land. And the idea was that

Speaker 3 the moon got sort of, as it were, plucked out of

Speaker 3 that area. Well,

Speaker 3 the Earth might have been rotating very quickly and the two split apart, for example.

Speaker 3 Dynamically now known to be absolutely impossible. So didn't happen like that.

Speaker 3 Another idea is that

Speaker 3 the moon was captured from some

Speaker 3 distant time in the past, that there was an accidental encounter between

Speaker 3 the moon and

Speaker 3 the earth and the moon got sort of flung into orbit around

Speaker 3 the Earth.

Speaker 7 So this planet is drifting across the universe and it hits the gravitational pull of the Earth and

Speaker 7 stays there.

Speaker 3 That sort of thing.

Speaker 3 Possibly not drifting across the universe but drifting across the solar system anyway.

Speaker 3 Or maybe the moon and the and the earth were formed together at the same time.

Speaker 3 The planets were formed out of little whirlpools in a nebula of dust and rocky stuff that was swirling around the solar system, little eddies in it, and maybe there was a double eddy where we were and two things condensed both at the same time and next to one another.

Speaker 3 And so we have a a moon and the earth.

Speaker 7 Is that the prevailing theory?

Speaker 3 No.

Speaker 3 The theory now, which has been current since about the mid-80s,

Speaker 3 is a theory which is facetiously called the big splash or the big splat,

Speaker 3 which is that early on in the history of the solar system,

Speaker 3 there were a number of embryonic planets, and

Speaker 3 two of them encountered one another and actually collided. That

Speaker 3 one of them was the proto-Earth, and the other was

Speaker 3 a planet which is about Mars-sized and has been given the name of Theia, who was the Titan, who was the mother of Selene, the moon goddess.

Speaker 3 And these two objects collided, one against the other.

Speaker 3 Each of them was

Speaker 3 a planet with an iron core, and the two iron cores coalesced together into a single iron core.

Speaker 3 Each of them had a rocky mantle and a crust around them, and the rocky mantles and the crusts all crumpled up

Speaker 3 in this impact. A lot of the rocky stuff condensed back onto the Earth, but a lot of the rocky stuff condensed into a separate body, assembled itself in orbit.
That's the Moon.

Speaker 3 So the idea is that it was a chance event, a completely flukey, lucky,

Speaker 3 possibly unique event, quasi-unique event in the very early history of the solar system. How long did it create?

Speaker 7 What's the very early history?

Speaker 3 Well, we're talking the the solar system is four and a half billion years old and we're talking soon,

Speaker 3 soon in the history of the solar system.

Speaker 7 Ian Crawford, can we that's now the most favoured explanation, yes, you're nodding away, say it is.

Speaker 7 Why is it most favoured? Can we just talk about this dust? Paul refers to this dust swirling around and what dust what's the dust?

Speaker 11 Well, it's the consequences of the impact of this hypothetical planet Thaya with the proto-Earth, as Paul said.

Speaker 7 I thought this was before the impact. Well, this is after the impact.

Speaker 3 There is dust.

Speaker 3 Dust is ubiquitous. Every time you get solids, you get dust.
But there was dust that was formed

Speaker 3 rotating in a disk around the Sun at the time that the Sun was formed. Originally, that dust was

Speaker 3 from

Speaker 3 supernovae and other events in the celestial universe, in the stellar universe.

Speaker 3 And that created a dusty disk.

Speaker 7 Can I just come back to the dust? So, what's in the dust? I mean, the dust's in us, we know that, but what's in the dust?

Speaker 11 If we're talking about the debris from which the moon formed, according to the giant impact theory, then that is a mixture of fragments of the Earth's mantle that was knocked off when this Thayer object struck the Earth, and fragments of Thayer's mantle.

Speaker 11 And it's all mixed together.

Speaker 11 Now, the reason this is currently the most popular theory, because it seems an extravagant theory at first sight, why we've got these giant planets flying around like loose cannons in the solar system.

Speaker 11 Having to appeal to something that seems unlikely is not a scientist's first instinct.

Speaker 11 But the reason that lunar science has latched on to this theory for the formation of the Moon really, again, is a consequence of our understanding of what the Apollo samples have told us.

Speaker 11 And it's this: that the Moon is similar in bulk composition to the Earth, but not identical, and with two major exceptions.

Speaker 11 The first is the Moon has,

Speaker 11 if it has an iron core at all, it's got a very small core because its average density is so low, three and a half grams per cubic centimeter instead of five and a half, which is the Earth's density.

Speaker 11 So your theory of the Moon has to explain why the Moon doesn't have a large iron core.

Speaker 11 And the other thing we've learnt from the Apollo samples is although the rocks and minerals are similar to those found on the Earth in many respects, they're extremely deficient in volatiles.

Speaker 11 So they're very deficient in water, they're very deficient in sodium, they're very deficient in all the chemical potassium, they're very deficient in all the chemical elements that have a low boiling point.

Speaker 11 And so

Speaker 11 the giant impact theory explains both of these quite well, because when you have these two planetoids colliding, the cores, if Thaya had a core, it merges with the core of the Earth.

Speaker 11 Then you've made the Moon out of just the silicate component of the early Earth and Thaya.

Speaker 11 And then collision will be a very violent, very energetic event, and the volatile substances will be boiled off and evaporated away.

Speaker 11 So, what you're left with to build a moon out of is Earth-like stuff minus the iron core minus the volatiles.

Speaker 11 And so, this explains the chemical composition of the moon well, but it's also, as Paul said, very consistent with our current understanding of the way the solar system was formed, with many, many planets, many, many planetlets, planetesimals in eccentric orbits crashing into each other.

Speaker 7 Colonel Crowder, can I go back to the beginning of the serious study of the moon, which is credited to Galileo with his observations in 1609?

Speaker 7 Maybe a passing reference to Thomas Harriot, an Englishman who pointed to telescope at the moon in the same year, but his sketches weren't all that good and he didn't follow it through.

Speaker 7 Galileo's our man.

Speaker 7 How did his perceptions and what he

Speaker 7 affect people in such a profound way? Because he did change the nature of discourse, didn't he?

Speaker 10 It really did. And he was the first person to try and make sense of what you could see through the moon through this very crude optical telescope that was developed in 1609.

Speaker 10 And anybody can reproduce this sense of awe. If you just look at the moon through simple binoculars now, it changes from being just this sort of perfect disk with dark splodges on.

Speaker 10 You start to see structures on the moon. And particularly,

Speaker 10 like Galileo did, you look at the dividing line between night and day on the moon. So that means on the moon, that's sunrise or sunset.
It's where you get the longest shadows.

Speaker 10 And he could see that there were mountains on the moon, that there were these bowl-shaped depressions that we call craters on the moon, casting shadows.

Speaker 10 And from those shadows, he could start to estimate the height and just basically determine that the moon had a rugged landscape. It was similar to the Earth.

Speaker 10 It brought the Moon much closer to something we could understand and we could contemplate.

Speaker 10 It made it much more, we could connect to it a lot better than just it being this sort of silver orb in the sky that we knew nothing about.

Speaker 7 But it also brought reality into an area that had been almost mythological, hadn't it? The moon was the perfect sphere.

Speaker 7 It was up there, it represented all sorts of things, but its perfection and its spherical perfection were what mattered. And he said, no, it's like us, it's full of bumps and grinds.

Speaker 10 Yeah, it's just like the Earth. It has a landscape, it has this topology.
And yes,

Speaker 10 it is very much another planet that's very similar to the Earth, not some perfect celestial sphere in the sky.

Speaker 7 Can you remind us of the initial impact of his views?

Speaker 10 Well, again, it's this idea that the heavens were perfect really that had been left over from the Greeks and Aristotle ideas and again it's just challenging the way that we viewed the whole solar system and of course it's wound into his observations of Jupiter and of the Milky Way.

Speaker 10 It's just one of his many challenges to the view that had prevailed for centuries beforehand.

Speaker 7 And we got closer and closer Ian Crawford and to the moon and then we sent spacecraft there to look at big close-ups.

Speaker 7 What did they discover? How far in advance were they from Glalaire?

Speaker 11 I think it was obviously it was a huge paradigm change in our understanding of the moon because telescopic astronomy had made major progress studying the near side but can't see the far side at all from the earth and so spacecraft finally enabled us both to see the far side and to make much more detailed observations of both near and far side and eventually of course to land scientific instruments on the surface and to bring and to bring bring samples back.

Speaker 11 So most of this started in 1959 so only two years after Sputnik, within two years of Sputnik,

Speaker 11 there will be a series of very successful

Speaker 11 Russian spacecraft.

Speaker 11 The first flyby of the moon, the first spacecraft to hit the moon, and the first spacecraft Khrushchev to take images of the far side, Luna 3, all occurred in 1959.

Speaker 11 It's revolutionised our knowledge, I would say.

Speaker 7 And then the Americans took up the fight. It became a political struggle, didn't it, Paul?

Speaker 7 Race, really. And

Speaker 7 Kennedy said he was going to put an astronaut on the moon by the end of the decade, and by the end of the decade, 1969, he did. What was significant about this?

Speaker 3 Well,

Speaker 3 Russia, the Soviet Union as it was then, and the United States were competing, of course, in the Cold War. and

Speaker 3 each wished to demonstrate dominance in armaments, in strike capability against the other side.

Speaker 3 And space was an arena where that competition took place without actually having to go to war.

Speaker 7 Did

Speaker 7 almost serve a pacifying purpose?

Speaker 3 I think you could argue that, yes. I think you could argue that

Speaker 3 a bit like the Olympic Games, I suppose, you know, a lot better to compete one nation against another

Speaker 3 in a peaceful way than to compete in

Speaker 7 a global war.

Speaker 3 Quite clearly so.

Speaker 3 The competition,

Speaker 3 of course,

Speaker 3 you can't completely compete,

Speaker 3 you haven't got the resources to compete in a completely unscaled sort of way.

Speaker 3 And the competition boiled down, in fact, to the USSR

Speaker 3 concentrating a lot on establishing a permanent station orbiting around the Earth, a space station like Mir.

Speaker 3 And the United States

Speaker 3 declared that it was going to go to the moon and

Speaker 3 establish the manned exploration of the moon. Kennedy set that as a goal

Speaker 3 for NASA

Speaker 3 and

Speaker 3 much, I might say, to everybody in NASA's surprise, it came completely out of the blue for them.

Speaker 3 And they went ahead and did it, even though it was a very dangerous and risky thing to do.

Speaker 7 Carolyn, can you tell us, would the discoveries made by the men who got to the moon, could they have been done by robots? What they brought back, could that have been done by robots?

Speaker 10 Oh, that's an interesting that's an interesting point. I mean, as Paul says, the primary reason for going to the moon was not scientific returns.
However,

Speaker 10 again, as been mentioned so far in the programme, these 382 kilos of samples of rock and soil that the Apollo scientists brought back were crucial in you know building up this whole picture about the formation and the evolution of the moon.

Speaker 10 Now, strictly speaking, we could have collected those samples robotically.

Speaker 10 The Russians proved this with their lunar programme. They were collecting lunar samples.

Speaker 10 And we could have perhaps collected them from a wider range of sites on the Moon rather than just these six very safe Apollo sites.

Speaker 10 However, there were other scientific returns from the Apollo mission in that the astronauts set up scientific experiments on the surface, so measuring the seismic activity of the Moon.

Speaker 10 They put a reflector on the Moon where we bounce laser signals off it. And that's, for example, how we can say with such accuracy the moon is moving away at four centimetres a year.

Speaker 10 And to actually install experiments like that on the surface, there's a lot of human decision about where you site the experiment, how you align the experiment, how you check it's working.

Speaker 10 And that would have been very... maybe it would have been possible but very difficult to achieve very efficiently through robotic means.

Speaker 10 So I think with any space exploration you need the initial reconnaissance from the spacecraft followed by the subsequent human exploration?

Speaker 11 Yes, I very much agree with that. I mean, I think it's inconceivable that we would know as much about the moon now had the Apollo missions not occurred 40 years ago.

Speaker 11 I mean, it's true that the Russian lunar programme,

Speaker 11 there were three, lunar 16, 20, and 24, returned with about 100 grams of lunar material each. But this is 0.1% of

Speaker 11 the 380 kilograms returned by Apollo. But in addition to that, the Apollo selection is much more diverse because the astronauts had had such mobility, particularly in the later missions.

Speaker 11 It's a much more diverse set of samples, plus the installation of the geophysical instruments that Carolyn has mentioned.

Speaker 11 So some of it could have been done robotically, some of it not, but I still think had it not happened, we'd know less about the moon now than we do.

Speaker 7 Paul, I know you're Paul Mann, I know you're coming, but could you also

Speaker 7 jump to the 90s when the next spacecraft went?

Speaker 7 But you were going to say something.

Speaker 3 Well, I was going to say that it seems to me quite common

Speaker 3 in the history of space exploration to see two completely different threads

Speaker 3 for

Speaker 3 the way science interacts with space exploration.

Speaker 3 In some cases, it's the science that leads. The scientists have a problem, they articulate the problem, they send a spacecraft to attack the problem.

Speaker 3 The fact that that develops space capability is a kind of a spin-off from that, that everybody's very happy to accept, but it's a spin-off from the scientific drive.

Speaker 3 In the case of the Apollo missions and some others,

Speaker 3 you see some geopolitical sort of

Speaker 3 aim

Speaker 3 being articulated and being thrust towards,

Speaker 3 and the scientists hitch a ride on that.

Speaker 3 They exploit that opportunity. Somebody's going to go to the moon.
Let's have a geologist go to the moon and

Speaker 3 let's pick up what we can.

Speaker 7 Carlin, until relevantly, until relatively recently, there was thought to be no water on the moon. Now the water is somewhere on the moon frozen and so what difference does that make?

Speaker 10 It makes a huge difference to the potential for exploration of the moon because if you could I mean anything you have to launch into orbit to the moon costs money.

Speaker 10 It's hideously expensive to send things out into space.

Speaker 10 So if you can find some of those resources that you need for exploration of the moon, especially a human presence on the moon, it makes things much more viable.

Speaker 10 So if there's frozen water on the moon, you have the potential to break it into its constituent parts, hydrogen for, say, rocket fuel, oxygen for air you breathe, water potentially for astronauts to drink or to use for crops.

Speaker 10 It just makes it a much more viable possibility. However, there's not that much water on the moon.

Speaker 10 I mean, yes, there's water on the moon, and if you'd asked us this 20 years ago, we would have said it was completely dry. We now know there's water on the moon, but it's not much.

Speaker 10 It's still drier than anywhere on Earth. It would take, you know, probably like a thousand tons of moon rock to get squeeze out one litre of water.
It's not not very much at all.

Speaker 11 Well, it depends slightly more than that. It depends.
Mo most of the the evidence for ice is in the polar craters, which never see the sun, where it's always

Speaker 11 always very cold and water ice is stable.

Speaker 11 Two years ago, there was a spacecraft called LCROSS, which lashed, which was deliberately designed to crash into one of these polar craters to see how much water vapour was released.

Speaker 11 And the estimates of that were 5% by weight in the regolith

Speaker 11 in the bottoms of these permanently shadowed craters. So 5% by weight, a cubic metre is about 1,700 kilograms of regolith.

Speaker 11 So I think you're 10 to 20 litres potentially per cubic metre, which is a lot. But of course only, you are right, globally, water is very rare.

Speaker 11 So only in these very specific localities is there possibly quite a lot of water.

Speaker 10 Yes, so it's only really in those parts and ecratic in permanent shadow down by the pole. So you're right, but only in these very specific locations.

Speaker 10 And those are going to be the potential targets if we ever do establish a lunar outpost.

Speaker 7 Almodin, do you think the moon is going to be colonised?

Speaker 3 I think it will be, yes.

Speaker 7 Why? I mean, doesn't it is it for other purposes, for the moon itself? Because a lot of people would say, well, what have we got out of the moon?

Speaker 7 There are these rocks, but they're more like rocks on the earth than anything else.

Speaker 7 So what's coming from it that justifies the expense of going there in the first place?

Speaker 3 Well I think you have to take a very long-term view

Speaker 3 and the long-term view is

Speaker 3 driven particularly from

Speaker 3 the former communist countries from a Marxist ideology

Speaker 3 where

Speaker 3 the outward exploration and

Speaker 3 onward progress of mankind is something which is in in inherent and inevitable in the progress of history.

Speaker 7 So you're talking about ideology, not scientific.

Speaker 3 If you talk in terms of where mankind is going to go,

Speaker 3 is mankind going to go out to the solar system, then I think that

Speaker 3 the first place to establish colonies outside of the Earth is going to be Narsa.

Speaker 7 Is that just because there's a launching pad and it takes us a bit nearer Mars?

Speaker 3 I think from our point of view, yes, from a Western point of view, I think that's right.

Speaker 3 From a Chinese point of view, I think there is inherent value in having a Chinese colony on the Moon.

Speaker 7 What's inherent about it?

Speaker 7 Just to show they can do it?

Speaker 3 To show that they can do it, and because it's inevitable that they do do it.

Speaker 7 Well, they think in the theology. Oh, I see.
It's a theological. Yes.
Oh, I see. I get it.
Right. Carolyn.

Speaker 10 There's also a view that the moon is a potential mineral resource.

Speaker 10 Okay, so a lot of the missions from the 1990s and in the 2000s are mapping the moon, trying to work out in more detail what possible resources are on there.

Speaker 10 And one of, perhaps it's a bit far-fetched, but one of the resources that some countries are interested in is the possibility of an isotope of helium called helium-3.

Speaker 10 So this is helium with two protons and one neutron in the nucleus.

Speaker 10 And we think it is being it's been produced by the sun in enormous quantities and the sun sort of sprays this out into space in the solar wind. And this soil, this broken down

Speaker 10 regolith that's on the surface is very fine-grained material. It absorbs the helium-3 that the sun spits out.

Speaker 10 Now, so we think certainly in the older surfaces of the moon, you've got a lot of helium-3 trapped in, and this is important potentially as a very safe nuclear fusion fuel.

Speaker 10 And so, the idea is that if it is found in vast quantities on the moon, we can potentially mine it and bring it back to Earth as a future, very safe, very efficient fuel source.

Speaker 10 The problem, though, again, is you've got to go through a lot of the the regolith to find the helium three so you would effectively be looking at strip mining the moon to get this this fuel source out.

Speaker 11 Well I think so looking for future resources on the moon is is is a possible justification for renewed a renewed human presence on the moon. I agree with that.

Speaker 11 I think we can debate whether helium three is likely to be economically practical and I I personally have my doubts about that. But whether it is or not,

Speaker 11 I think there is a lot of scientific

Speaker 11 the moon still has a lot to tell us about the history of this solar system and our place within it and in particular

Speaker 11 just as the lunar regolith is soaking up helium-3 it's soaking up the rest of the solar wind as well so even if that's not economically useful there is a record there of the evolution of the sun throughout the last four and a half thousand million years potentially preserved in these regolith deposits regardless of whether they're economically useful they tell us a lot about the early sun that unless we build a time machine we'll otherwise won't be able to access

Speaker 11 And there's also the possibility that meteorites, just as we have meteorites from the moon, which I haven't actually talked about yet, but we do have meteorites from the moon that have landed on the earth, it's highly likely that meteorites from the earth will have landed on the moon.

Speaker 11 And there's a whole missing dark age in terrestrial geology, the first thousand million years of Earth's history, where the Earth has destroyed, eroded away its own crustal rocks.

Speaker 11 And perversely, if they're preserved anywhere, they may be preserved as Earth meteorites that were blasted off the early Earth four billion years ago, landed on the Moon, where potentially they've been kept as a kind of museum of solar system history, really,

Speaker 11 with a record of what our planet was like at the time life evolved on or appeared, originated on on the Earth. And we know very little about the conditions on the Earth at that early time.

Speaker 11 And the Moon may preserve a record. It may also preserve a record, just as it collects solar wind.

Speaker 11 There's some evidence that it collects molecules that have drifted out of the Earth's atmosphere and landed on the Moon and become incorporated in the regulatory.

Speaker 11 So there's a potential record there of the Earth's early crust, the Earth's early atmosphere, the Earth's early meteorite bombardment history.

Speaker 11 So actually, I think if we do go establish a lunar base or have a renewed human presence on the moon, there's actually a tremendous amount of

Speaker 11 science for these people to do.

Speaker 7 Do you agree with that, Paul?

Speaker 3 Paul Mernon? I do, yes. I mean,

Speaker 3 the moon is a palimpsest. Everything that's ever been written over the history of the solar system is recorded on the surface there.
There's the bombardment history

Speaker 3 on the surface, the history of all the meteors and asteroids.

Speaker 7 That's because it's got no atmosphere and things have to crash into it.

Speaker 7 And they don't burn on the way through the earth.

Speaker 3 It's had no weather. It's had no weather.
So everything that happened has left its mark.

Speaker 3 All those craters, huh? And that mark has not been

Speaker 3 eroded away.

Speaker 3 It has no plate tectonics. So the surface of the moon is not sort of churned over all the time.

Speaker 3 The history of the solar system is written there, if only you could read it.

Speaker 7 It's wonderful to think of the moon. I never thought of the moon as a museum, but there it is.
If we dig far and if we can find out things we don't know about the first billion years.

Speaker 11 Yeah, yeah, I think this is absolutely a crucially important reason for continuing the exploration of the moon.

Speaker 7 Isn't there a sense that the three of you have got tremendous intellectual vested interest in talking up the importance of the moon? Because the more it gets there, the more fun you have.

Speaker 10 Oh, yes.

Speaker 10 We haven't even touched on, for example, I'm an astronomer, the astronomy you could do from the moon. Far side of the moon, nice protection from all the radio signals from Earth, nice long days.

Speaker 10 The potential scientifically of a permanent base in the moon is is huge.

Speaker 15 I'm cooler than that.

Speaker 3 I used to be responsible for funding scientific projects and of course it's not just what you can do, it's how much it costs to do it and what you would get if you spent the same amount of money in some other way.

Speaker 3 So

Speaker 3 I think

Speaker 3 you have to have the enthusiasm, you have to have the vision and then you have to have the cold light of day where you look at the bottom line.

Speaker 7 I see. I saw your eyes narrow for the first time.
You put a scientific hand on Paul Murdoch,

Speaker 7 and suddenly the conversation cooled.

Speaker 3 That's what being associated with the civil service does for you.

Speaker 7 Ian Crawford.

Speaker 11 Well, I was just going to say, of course, Paul's right. If we're going to spend public money, we have to have to do so with our eyes open.

Speaker 11 But I think we talked earlier about China and international competition, and Apollo was a product of the Cold War. But I think there is a different model.

Speaker 11 I think we should be looking more now to having these expensive human space exploration programmes as truly international efforts, truly global efforts,

Speaker 11 which can then achieve, in addition to all the science,

Speaker 11 a unifying potential for having a non-violent, as Paul mentioned earlier, way of

Speaker 11 collaborating scientifically over the whole world.

Speaker 7 Well, thank you very much, Ian Crawford, Carolyn Crawford, and Paul Murden. And next week we'll be talking about the Philosophical Continental Analytic Split.
Thanks for listening.

Speaker 8 And when this edition was first broadcast, there was no extra content for the podcast.

Speaker 8 I can see, though, from the notes at the time, that as soon as the broadcast ended, Carolyn Crawford produced a lump of rock from the moon for everyone to inspect.

Speaker 8 Anyway, this edition was produced by Natalia Fernandez, and we'll have another of Melvin's most cherished episodes next week.

Speaker 8 In Our Time with Melvin Bragg is produced by me, Simon Tillotson, and it's a BBC Studios production.

Speaker 15 The figure's face was featureless and its entire body was jet black.

Speaker 3 I'm Danny Robbins and throughout October I will be sharing uncanny listeners, real-life ghost stories. That's one every single day as we count down to the spookiest time of the year.

Speaker 15 Suddenly, all hell lets loose. The sound of glass smashing, heavy objects being thrown, doors being ripped off hinges.
It was coming from the cellar.

Speaker 15 I looked up and and was staggered to see a humongous black triangle floating silently over the rooftop.

Speaker 3 Join me as Uncanny counts down to Halloween every day in October on BBC Sounds.

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