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.”