‘You’re all being silly,’ Miranda concluded. ‘By the way, I think it’s kind of blue. The moon, I mean. It’s almost eerie.’
‘Uhhh,’ O’Keefe shuddered.
‘So what colour is it?’ Olympiada wanted to know.
‘It’s every colour, and yet none.’ Julian Orley came through the connecting hatch that separated the living quarters of the Charon from the landing module. ‘No one knows.’
‘How come?’ Rogachev wrinkled his forehead. ‘I mean, surely we’ve had enough time to figure that out?’
‘Of course. The problem is that no one has seen it through anything other than toned or filtered windows and visors yet. And on top of that, the Moon doesn’t have a particularly high albedo—’
‘A what?’ asked Miranda, rotating like a pig on a spit.
‘Reflectivity. The fraction of solar energy which is reflected back to space. The reflection rate of lunar rock is not especially high, particularly not in the maria—’
‘I’m not following a word you say.’
‘The dry plains on the surface of the Moon,’ explained Julian patiently. ‘Collectively, they’re called maria. The plural of mare. They appear to be even darker than the mountain rings in the craters.’
‘So why does the Moon look white when we look at it from Earth?’
‘Because it has no atmosphere. Sunlight hits its surface unfiltered, in just the same way it would an astronaut’s unprotected retina. The UV rays outside are far more dangerous to our eyes than they would be on Earth, that’s why the spaceship’s windows are tinted.’
‘But loads of lunar samples have been brought back to Earth,’ said Rogachev. ‘What colour are they?’
‘Dark grey. But that doesn’t necessarily mean that the whole moon is dark grey. Perhaps some parts of it are brown, or even yellow.’
‘Exactly,’ said O’Keefe from behind his book.
‘Everyone sees it slightly differently. Everyone has their own moon, one might say.’ Julian went over to join Evelyn. They were passing over a lone gigantic crater which lay far below them. Molten light seemed to stream from its slopes down to the surface surrounding it. ‘That’s Copernicus by the way. According to popular opinion it’s the most spectacular of all the lunar craters and over eight hundred million years old. It’s a good ninety kilometres wide, with slopes that would present a challenge to any mountaineer, but the most impressive thing about it is how deep it is. Do you see that massive shadow inside it? It’s almost four kilometres down to the very bottom.’
‘There are mountains right in the middle of it,’ observed Evelyn.
‘How is that possible?’ wondered Olympiada. ‘I mean, in the middle of the point of impact? Shouldn’t it all be flat?’
Julian fell silent for a while.
‘Imagine it like this,’ he said. ‘Picture the surface of the Moon, just as you see it now, but without Copernicus. Okay? Everything is still and peaceful. So far! Then, a boulder eleven kilometres in diameter rushes up from the depths of outer space at a speed of seventy kilometres per second, two hundred times the speed of sound. There’s no atmosphere, nothing at all that could slow it down. Imagine what kind of impact it would make crashing into the surface. That alone would happen in just a few thousandths of a second. The meteor would penetrate the surface by about a hundred metres – not particularly deep you might say, and an eleven-kilometre crater like that wouldn’t be such a big deal. But there’s a little more to it than that. The complex thing about meteorites is that they transform all their kinetic energy into heat at the moment of impact. In other words, they explode! It’s this explosion that can create a hole ten to twenty times bigger than the meteorite itself. Millions of tonnes of rock are blasted in all directions and, in a flash, a wall forms around the crater. The whole thing happens at such speed, the displaced layers of lunar basalt can’t be restructured as quickly, so the surface gives in to the shock pressure and is compressed many kilometres deep. Meanwhile, huge clouds of debris are collecting overhead. The meteorite, of course, is now fully transformed into heat and no longer exists in its previous form, so the ground rebounds, shooting upwards to form a massive peak in the centre of the crater. The rock clouds continue to spread rapidly and once again the absence of any atmosphere to contain the radius of the cloud makes itself felt. Instead the debris is flung further and further out before descending, hundreds of kilometres away, like billions of missiles. You can still see this ring of fall-out today, known as an ejecta blanket, especially when there’s a full moon. It has a different albedo to the darker volcanic rock around it, and seems to glow from within. In actual fact it’s just reflecting a little more sunlight. So, that’s how you should picture Copernicus coming about. Victor Hugo, by the way, claimed to see an eye within it that looked back at whoever was looking at the Moon.’
‘Uh-huh,’ said Olympiada dejectedly.
Julian smiled knowingly to himself, relishing the awkward silence that followed his account. All around him cosmic bombs were crashing into their thoughts and converting kinetic energy into questions such as, in the event of a similar impact threatening Earth, whether it would be better to seek refuge in the cellar or to go for one last beer.
‘I guess our atmosphere wouldn’t be of much help?’ Rebecca Hsu suggested.
‘Well…’ Julian pursed his lips. ‘Meteorites are always plummeting down to Earth, around forty tonnes of them a day in fact. Most of them are the size of a grain of sand or pebble and end up burning themselves out. Now and again one the size of a fist will come along, and occasionally something bigger will crash into tundra or the sea. In 1908, for example, a sixty-metre-wide fragment of a comet exploded over Siberia and devastated an area the size of New York.’
‘I remember hearing about that,’ said Rogachev drily. ‘We lost some forest, a few sheep and a shepherd.’
‘You would have lost a lot more if it had hit Moscow. But yes, in the main, the universe is essentially past the worst. Meteorites like the one that caused Copernicus have become few and far between.’
‘How far between exactly?’ drawled Heidrun.
Julian pretended to give it some thought. ‘The last really significant one came down sixty-five million years ago in the area that’s now known as Yucatán. The shock-waves travelled all around the world, causing several years of continuous winter, which led to the loss of considerable amounts of flora and fauna, and unfortunately, almost all the dinosaurs.’
‘That doesn’t answer my question.’
‘You really want to know when the next one will hit?’
‘Just for my own planning purposes, yes.’
‘Well, according to statistical data there’s a global catastrophe every twenty-six million years. How catastrophic exactly depends on the size of the impactor. An asteroid seventy-five metres in diameter has the explosive force of one hundred Hiroshima bombs. Anything exceeding two kilometres can trigger a global winter and would mean the end of mankind.’
‘So, according to that we’re forty million years overdue,’ established O’Keefe. ‘How big was the dinosaur-killer again?’
‘Ten kilometres.’
‘Thank you, Julian, I’m very glad you’ve brought us up here away from it all.’
‘So what can we do about it?’ asked Rebecca.
‘Very little. The nations with space programmes have avoided dealing with the problem for years, preferring instead to devote their energy to building up an expensive battery of mid-range missiles. But what we really need is a functioning meteorite defence system. When the hammer falls it won’t matter whether you’re a Muslim, Jew, Hindu or Christian, atheist or fundamentalist, or who you’re fighting with, none of that will matter. Crash, and that’s it! We don’t need weapons against each other. What we really need is one that can save us all.’