“In the open sea?” Shafer asked.
“In the open sea. Tsunamis are long-range, because the ocean is a surface and specific energy drops linearly with distance rather than inverse square. An earthquake in Chile in 1960 created ocean waves which travelled over ten thousand miles and killed a lot of people in Japan.”
“What was its wave height?” McNally asked, coming back from the window.
“In the open sea, twenty centimetres. The wavelength is hundreds of kilometres.”
“An eight-inch wave killed people?” McNally asked, bewildered.
Sacheverell winced. “No. When the wave runs into shallow water the same amount of energy is being carried by less and less water. So when it approaches a shoreline it rears up. The twenty-centimetre wave became a metre or two high. Killed a couple of hundred people, if you count the ones that just went missing.”
“So what’s the run-up factor on your fifteen-metre wave, Herb?” Shafer asked.
“Ten to forty, depending on the shoreline. If we say twenty, the wave is three hundred metres high when it hits land, assuming the impact was a thousand kilometres offshore.”
“The height of the Eiffel Tower,” Leclerc said. “How far inland would a wave like that travel?”
“Again it depends. Topography, roughness of surface. Flat agricultural land would flood for ten or twenty kilometres inland. When I say flood, I mean the wave is still two hundred metres high maybe five kilometres inshore.”
Webb said: “An Atlantic splash of that order would take out nearly all the major cities in Britain.” Although he was actually trying to visualize a half-mile tsunami roaring up Glen Etive.
“I don’t believe these figures,” Shafer said, without bothering to explain why.
“Europe is protected by a steep continental shelf,” Sacheverell informed Webb. “It reflects about three quarters of the energy back into the ocean.”
“Great,” Webb said. “Really great. Now I know that when I turn into Piccadilly the wave coming at me is only a hundred metres high.”
Noordhof went to the percolator and came back with a refill. “And if Baby Bear hits land?”
“Blast, heat and earthquake. The blast is a pressure pulse followed by a hot wind. The nuclear weapons people use an overpressure of four psi to define total devastation although there’s huge loss of life even at two, mainly from blizzards of flying glass in urban areas. Hit L. A. and you’ll blow the
roofs off houses in San Diego. A Baby Bear on Philadelphia would rip people up from Baltimore in the south to New York in the north.”
“You could take out England from London to Newcastle,” Webb interrupted, still doing his patriotic bit.
“Who would want to zap your feeble little island?” Sacheverell asked. “I’ve taken the threshold for fire ignition to be about a kilowatt applied to a square inch for a second. It turns out you ignite everything in sight—tyres, grass, everything flammable. A hundred miles away, it’s like standing four inches from an electric fire for ninety seconds.”
“That must depend on whether the asteroid hits the ground or breaks up in the air,” said McNally.
“No. The heat comes from the hot wake trailing the fireball. Lastly, earthquake. I’ve taken Gutenberg-Richter Nine as defining total devastation, and I’ve assumed five per cent of the kinetic energy goes into shaking the ground. We’re looking at Nine over a region about a thousand kilometres across.”
Noordhof took a sip at his coffee. “So Baby Bear takes out a few cities or floods one of our seaboards. But it doesn’t totally destroy the USA and it leaves our nuclear potential intact. So let’s turn the screw a bit. Herb, take us to Mummy.”
“Wave height scales as the square root of the impact energy, and the flood plane extends as the four thirds power of the run-up wave. These are approximations. They’re beginning to crumble when you get to the really big numbers. Mummy Bear makes an open ocean wave fifty metres high a thousand kilometres away. The run-up factor stays the same so you hit the coast with a wave a kilometre or two high. I guess the Rockies or Appalachians would protect the central USA. For an Atlantic impact, I don’t know how much of Europe would be left.”
Shafer said: “That’s just movie stuff. A wave that big would break up. The tsunami would only take out a few million people.”
Noordhof interrupted: “Our Kansas silos stay intact.”
Shafer said, “But you’re not expected to shoot back. This is just a great natural disaster, right?”
“And a land impact? Blast, heat, earthquake?” Noordhof’s voice had an edge to it.
“Ten times the impact energy gives you ten times everything else. And a sixteen-mile crater as a bonus.”
“I don’t like the sound of that,” Noordhof said. “You want to tell us about Big Daddy?”
“Give me an extra power of ten and I’ll shower the States with ballistic ejecta. At the impact site, everything as far as the horizon vaporizes. It gets thrown above the atmosphere, recondenses as sub-millimetre particles at a thousand degrees and falls back over an area equal to the USA. Allowing for heat lost to space etcetera I find that the thermal radiation at the surface is about ten kilowatts per square metre for an hour or more after impact. It’s like being inside a domestic oven. Try to breathe and your lungs fry. The whole of the United States turns into one big firestorm. I guess nothing would survive.”
Sacheverell tidied up his papers to show he was finished. There was a thoughtful silence. Webb broke it by saying, “These computations all have big uncertainties. My reading is you’d have less earthquake and more heat. You’d burn the States even with Mummy Bear. Partly I’m thinking of the Shoemaker-Levy 9 comet fragments which hit Jupiter in 1994. We had a coherent stream of material which gave us twenty impacts on to the planet. The heat flashes from the fallback of ejecta were a hundred times brighter than those from the fireballs themselves.”
Shafer stirred his coffee. “Big Daddy is good news.” There was an astonished silence. Noordhof’s cup stayed poised at his lips.
Webb nodded. “I believe so, Willy. There are maybe a couple of a million cometary asteroids out there, any one of which could give us a hydrogen-bomb sized impact. They
probably happen every century or two. This century we had Tunguska in the Central Siberian Plateau on June 30th 1908. It came in low from the sun at about 7:15 a.m. That was ten to thirty megatons. Hundred megatonners come in every few centuries. They’ve been recorded as celestial myths in Hesiod’s
Theogony
and the like. If you go to a few thousand megatons, you’re probably into the Bronze Age destructions: the climate downturn, Shaeffer’s mysterious earthquakes in the Near East.”
“What has this guy been smoking?” Sacheverell asked.
“Do you accept your own impact rates? The ones you keep re-publishing?”
“What of it?”
“With a decent chance of a thousand megatonner in the last five thousand years?”
“Sure,” Sacheverell sneered. “Probably at the north pole.”
“So we had ten megatons in Siberia in 1908, a megaton in the Amazon in 1930, another few megs in British Guyana in 1935, but the five thousand years of civilisation before that were missile-free? And what about Courty’s Syrian excavations showing Bronze Age city destructions caused by blast? And when Revelation talks about a great red dragon in the sky throwing a burning mountain to earth, and the sun and moon darkened by smoke, and the earth ablaze with falling hail and fire, and a smoking abyss, and the same celestial dragon keeps appearing throughout the Near East, in Hesiod in 800 BC, Babylon in 1400 BC and so on, and Zoroaster predicts a comet crashing to Earth and causing huge destruction, this is all poetic invention, drawn from a vacuum, based on no experience? You are aware, Herb, that comets were described as dragons in the past? That a great comet has a red tail? You have actually heard of Encke’s Comet and the Taurid Complex?”
Sacheverell’s face was a picture of incredulity. “I can’t believe I’m hearing this. You are seriously telling us that responsible policymaking should be based on a Velikovskian
interpretation of history? You want to throw in the Biblical Flood? Maybe von Däniken and flying saucers?”
“This is breathtaking,” Webb said. “We’re dealing with a threat to hundreds of millions of lives, and you think you can responsibly ignore evidence of past catastrophe just because you don’t have the balls to handle it?”
Sacheverell stabbed a thin finger. His voice was strident and the eyes behind the thick spectacles were angry. “You want to identify gods with comets and combat myths with impacts? What sort of a scientist do you call yourself? I say you’re a charlatan.”
“That’s it, Herb, go with the flow like a good little party hack. I say stuff your cultural hang-ups and your intellectual cowardice.”
Judy had frozen, mouth wide open to receive a hardboiled egg. Shafer was grinning hugely. Noordhof, his face taut with anger, punched a fist on the table. “Enough! Now get this. I could spend hours listening to you guys at each other’s throats. Unfortunately we don’t have hours to spend. Now simmer down. Ollie, get to the point. Explain to those of us down here on Earth why Big Daddy is good news.”
Sacheverell sat down heavily, flushed and rattled. Webb said, “Because we could spend two or three thousand years looking for Herb’s Little Bears. Because we have a better chance of detecting Big Daddies further out. And because we can maybe hit a big one harder without breaking it into a swarm.”
Shafer brushed his grey hair back from his shoulders with both hands. “And because the actuarial odds are that we’ve been hit by a few Tunguskas and maybe even a Baby Bear or two in the historical past, but civilization survived. The damage is relatively local. If you want to utterly destroy America, you have to go for bodies between half a kilometre and two kilometres across. Too little, and you leave the surviving States with lots of muscle and fighting mad.”
“You guys are wrong,” McNally said. “We’re only fighting
mad if we know the impact was an act of war. And like Herb said, we’re not supposed to know that. Look, even with the Baby Bear scenario you have an America with half its population wiped out, its industrial base gone, no political infrastructure, probably just chaos and anarchy. This is a gun society. We’d destroy ourselves, finish the job the Russians started. Zhirinovsky could do what he liked, where he liked and we’d be too busy to care.”
Shafer said, “Jim, you just want a Baby Bear because it’s easy to shift.”
Noordhof lowered his head pensively. Then he said, “I go with McNally. The uncertainties are too large for confident statements about the political intentions of the enemy, whether to incapacitate us or utterly destroy us. We conduct the scope of our search to encompass the full range from Baby Bear to Big Daddy.”
“Forgive me, but that is utterly impractical,” said Kowalski. “If you want to go down to ten thousand megatons you have to reach extremely faint limiting magnitudes. Which means very long exposures even with quantum-limited CCDs. You could wait a hundred years, as Oliver says. Upstairs, in zero moonlight, we can only go to magnitude twenty-two visual at solar elongations more than seventy-five degrees.”
Shafer said, “If you’re drunk and you lose your keys you look under the street lamp. Not because they’re necessarily there, but because that’s where you have the best chance of finding them. Meaning, we go for what’s practical. Extremely faint magnitudes take too long.”
Webb piled on the pressure. “You’re wrong on this one, Mark. The important thing is to cover the whole sky as fast as possible, and keep covering it until Nemesis swims into the field of view. Let’s just hope Nemesis is a big one. That way we have a chance of finding it while it’s still far out. And we get maybe months of warning. I say we aim for full sky coverage in a week. We should go for ten-second exposures on Kenneth’s supernova hunter, limiting magnitude seventeen.”
Noordhof looked at Sacheverell, who nodded reluctant agreement. The soldier said, “Okay I guess I’ve been flamed. Forget the Baby Bears. For now.”
Shafer asked, “Can you fix Pan-STARRS for us, Colonel? Give instructions for a magnitude seventeen search?”
“I’ll do better. We’ll control the telescopes remotely from here. We’ll use encryption in both directions.”
“We can spread it around,” Shafer suggested. “Route it through half a dozen sites.”
“Flagstaff and Spacewatch Two have preset sky search regions to avoid overlap,” said Kowalski. “I’ll set up the patrol to do likewise. Christ knows we have plenty of unmapped sky.”
Noordhof took a cigar out of a top pocket and started to unwrap the cellophane. “Right. We now have an observing strategy. We know what we’re facing if we can’t find this thing, and we know we’re fighting hellish odds. It’s a start.” He produced a match, struck it underneath the table, glanced at his watch, lit up and carried on speaking all at once.
“I know we all need a break but time’s moving on. So we’ll split into teams. Kowalski and I will set up liaison with Pan-STARRS and the other observatories. McNally and Shafer will come up with a deflection strategy. Do it, I don’t care how. Webb will tell us why we’re going about this the wrong way. Liaise with Leclerc, as he suggests. Sacheverell, you’re due to brief the Chiefs of Staff and the President on the impact scenarios later today.”
“What?”
Noordhof grinned sadistically. “What’s the beef, Herb? You have five hours and maybe you’ll even find time to shave. Prepare something non-technical, maybe a movie. This is your schedule: At thirteen hundred, you’re collected upstairs by chopper and transferred to a jet at Kirtland Air Force Base. You arrive Cheyenne Peak at fifteen hundred and brief the brass. They’re fixing up a little simulation and want your help. At twenty hundred you sit in on a DCI briefing in
Washington and at twenty-one hundred you brief the President.”
Sacheverell, looking stunned, appealed to Judy Whaler. He tried another angelic smile. “Can you help me? Maybe with some simulations.”
Judy gulped down the last of her boiled egg, gave Noordhof a look of disbelief and said, “Give me an hour, Herb. I need to talk to Ollie.” Sacheverell scurried out of the room, shoulders hunched, heading either for the conference room or a toilet.