Lucifer's Hammer

by Larry Niven

  “We’re interested in the probe,” Harvey said. “Does it look as if it will really go?”

  Sharps smiled broadly. “Looks good, looks good. Thanks to Senator Arthur Jellison. Remember our conversation about that?”

  “Right.”

  “Well, he’s the man. I’d appreciate any good publicity you can give him.”

  Harvey nodded. He signaled to the crew. “Let’s run it.”

  “Speed,” Manuel said. Charlie was behind the camera. Mark stepped out with the board. “Sharps interview, take one.” Clack.

  “Dr. Sharps,” Harvey said, “there’s been some criticism of the proposed Apollo mission to study the comet. It’s said it will be too dangerous.”

  Sharps made a gesture of dismissal. “Dangerous? We’ve done it all before. A tried-and-true booster and a proven capsule. Not so many months of planning as NASA likes, but ask the men who’ll fly it. Ask the astronauts if they think it’s too dangerous.”

  “Has the crew been chosen yet?”

  “No — but there are forty volunteers!” Sharps grinned at the camera.

  Harvey went on with his questions. They talked about the instruments the Apollo would carry. Many of them were being put together at JPL, and at Cal Tech. “Students and technicians working overtime without pay,” Sharps said. “Just to help out.”

  “Without pay?” Harvey asked.

  “Right. They get their regular work done, the things we have contracts for, and then put in overtime on comet packages. Without pay.”

  That ought to go well, Harvey thought. He made a note to interview some of the technicians. Maybe he could find a janitor who worked overtime to help.

  “It sounds like you can’t carry enough gear,” Harvey said.

  “Well, we really can’t,” Sharps agreed. “Not all we’d like to carry. But what’s enough? We can take up enough to learn a lot.”

  “Right. Dr. Sharps, I understand you’ve done a new plot of Hamner-Brown’s orbit. And you’ve got new photos of it.”

  “Hale Observatories has the photos. We did the orbit. We’re safe in saying it will be a big comet. It’s got the largest coma ever recorded for this distance from the Sun. That means there’s a lot of ice left in the snowball. And it’s going to come quite close. First it will pass at a reasonable distance, and we’ll see a spectacular tail. Then it goes inside the orbit of Venus and most of it will vanish, although some of the tail may be visible for a while. Naked-eye visible, I might add. After that it will be too close to the Sun for us to see from here, but of course the Apollo crew will be able to get good observations from space. We won’t see it again until it gets very near Earth on its way back out. By then the sky should be filled with the tail. I’m willing to bet that tail will be visible in daytime.”

  Mark Czescu whistled. Manuel didn’t glitch so Harvey knew it hadn’t got onto the tape. Harvey felt like whistling himself.

  The office door opened. In came a short, rounded, vague man, about thirty years old. He had a trimmed dark beard and thick glasses. He wore a green Pendleton wool shirt, and both pockets bristled with pens and pencils of every imaginable color and nib. A pocket computer hung at his belt. “Oh — sorry, I thought you were alone.” His voice was apologetic. He began to back out.

  “No, no, stay and hear this,” Sharps said. “Let me introduce Dr. Dan Forrester. His job title is computer programmer. His degrees say Ph.D. in astronomy; around here we usually call him our sane genius.”

  Mark was muttering behind Harvey. “If they call him a genius in this outfit…”

  Harvey nodded. He’d thought of that too.

  “Dan’s been doing more recasts of Hamner-Brown’s orbit. He’s also working on the optimum launch date for our Apollo, given the limited amount of equipment we can take, and the limited amount of consumables—”

  “Consumables?” Harvey asked.

  “Food. Water. Air. They take mass. We can only put up so much mass, and so we trade consumables for instruments. But consumables mean time in orbit. So Dan’s working on the problem: Is it better to launch earlier, with less equipment, so they can stay longer but get less information—”

  “Not information,” Forrester said. His voice was apologetic. “Sorry to interrupt—”

  “No, tell us what you mean,” Harvey said.

  “We’re trying to maximize information,” Forester said. “So the problem is, do we get more information by having more data about a shorter time, or less data about a longer time.”

  “Oh.” Harvey nodded. “So what have you got on Hamner-Brown? How far away at its closest point?”

  “Zero,” Forrester said. He didn’t crack a smile.

  “Uh — you mean it’s coming down our throats?”

  “I doubt it.” Now he smiled. “Zero within the limits of prediction. Which is a good half-million miles error.”

  Harvey relaxed. So, he noticed, did everyone in the room, including Charlene. They took Forrester seriously here. He turned to Sharps. “Tell us, what would happen if the comet did hit us? Suppose we got unlucky.”

  “You mean the head? The nucleus? Because it looks as if we might actually pass through the outer coma. Which is nothing more than gas.”

  “No, I mean the head. What happens? The end of the world?”

  “Oh, no. Nothing like that. Probably the end of civilization.”

  There was silence in the room for a moment. Then for another. “But,” Harvey said, his voice puzzled, “Dr. Sharps, you told me that a comet, even the head, is largely foamy ice with rocks in it. And even the ice is frozen gases. That doesn’t sound dangerous.” In fact, Harvey thought, I asked to get it on the record.

  “Several heads,” Dan Forrester said. “At least it looks that way. I think it’s beginning to calve already. And if it does it now, it will do it later. Probably. Maybe.”

  “So it’s even less dangerous,” Harvey said.

  Sharps wasn’t listening to Harvey. He rolled his eyes toward the ceiling. “Calving already?”

  Forrester’s grin widened. “Ook ook.”

  Then he noticed Harvey Randall again. “You asked about danger,” he said. “Let’s look at it. We have several masses, largely the same material that boils off to form the coma and the tail: fine dust, foamy frozen gases, with pockets where the really volatile stuff has been long gone, and maybe a few rocks embedded in there. Hey — ” Randall looked up at Forrester.

  Forrester was grinning his cherubic smile. “That’s probably why it’s so bright already. Some of the gases are interacting. Think what we’ll see when they really get to boiling near the Sun! Ook ook.”

  Sharps was getting that thoughtful, lost look again. Harvey said quickly, “Dr. Sharps—”

  “Oh. Yes, certainly. What happens if it hits? Which it won’t.

  Well, what makes the nucleus dangerous is that it’s big, and it’s coming fast. Enormous energies.”

  “Because of the rocks?” Harvey asked. Rocks he could understand. “How big are those rocks?”

  “Not very,” Forrester said. “But that’s theory—”

  “Right.” Sharps was aware of the camera again. “That’s why we need the probe. We don’t know. But I’d guess the rocks are small, from the size of a baseball to the size of a small hill.”

  Harvey felt relief. That couldn’t be dangerous. A small hill?

  “But of course that doesn’t matter,” Sharps said. “They’ll be embedded in the frozen gases and water ice. It would all hit as several solid masses. Not as a lot of little chunks.”

  Harvey paused to think that over. This film would take careful editing. “It still doesn’t sound dangerous. Even nickel-iron meteors usually burn out long before they hit the ground. In fact, in all history there’s only been one recorded case of anyone being harmed by a meteor.”

  “Sure, that lady in Alabama,” Forrester said. “It got her picture in Life. Wow, that was the biggest bruise I ever saw. Wasn’t there a lawsuit? Her landlady said it was her meteor becau
se it ended up in her basement.”

  Harvey said, “Look. Hamner-Brown will hit atmosphere a lot harder than any normal meteorite, and it’s mostly ice. The masses will burn faster, won’t they?”

  He saw two shaking heads: a thin face wearing insectile glasses, and a thick bushy beard above thick glasses. And over against the wall Mark was shaking his head too. Sharps said, “They’d bore through quicker. When the mass is above a certain size, it stops being important whether Earth has an atmosphere or not.”

  “Except to us,” Forrester said, deadpan.

  Sharps paused a second, then laughed. Politely, Harvey thought, but it was done carefully. Sharps took pains to avoid offending Forrester. “What we need is a good analogy. Um…” Sharps’s brow furrowed.

  “Hot fudge sundae,” said Forrester.

  “Hah?”

  Forrester’s grin was wide through his beard. “A cubic mile of hot fudge sundae. Cometary speeds.”

  Sharps’s eyes lit up. “I like it! Let’s hit Earth with a cubic mile of hot fudge sundae.”

  Lord God, they’ve gone bonkers, Harvey thought. The two men raced each other to the blackboard. Sharps began to draw. “Okay. Hot fudge sundae. Let’s see: We’ll put the vanilla ice cream in the center with a layer of fudge over it…”

  He ignored the strangled sound behind him. Tim Hamner hadn’t said a word during the whole interview. Now he was doubled over, holding himself, trying to hold in the laughter. He looked up, choked, got his face straight, said, “I can’t stand it!” and brayed like a jackass. “My comet! A cubic mile of hot… fudge… sun… dae…”

  “With the fudge as the outer shell,” Forrester amplified, “so the fudge will heat up when the Hammer rounds the Sun.”

  “That’s Hamner-Brown,” Tim said, straight-faced.

  “No, my child, that’s a cubic mile of hot fudge sundae. And the ice cream will still be frozen inside the shell,” said Sharps.

  Harvey said, “But you forgot the—”

  “We put the cherry at one pole and say that pole was in shadow at perihelion.” Sharps sketched to show that when the comet rounded the Sun, the cherry at the oblate spheroid’s axis would be on the side away from Sol. “We don’t want it scorched. And we’ll put crushed nuts all through it, to represent rocks. Say a two-hundred-foot cherry?”

  “Carried by the Royal Canadian Air Force,” Mark said.

  “Stan Freberg! Right!” Forrester whooped. “Shhhh… plop! Let’s see you do that on television!”

  “And now, as the comet rounds the Sun, trailing a luminous froth of fake whipped cream, and aims itself down our throats… Dan, what’s the density of vanilla ice cream?”

  Forrester shrugged. “It floats. Say two-thirds.”

  “Right. Point six six six it is.” Sharps seized a pocket calculator from the desk and punched frantically. “I love these things. Used to use slide rules. Never could figure out where the decimal point went.

  “A cubic mile to play with. Five thousand two hundred and eighty feet, times twelve for inches, times two point five four for centimeters, cube that… We have two point seven seven six times ten to the fifteenth cubic centimeters of vanilla ice cream. It would take a while to eat it all. Times the density, and lo, we have about two times ten to the fifteenth grams. Couple of billion tons. Now for the fudge…” Sharps punched away.

  Happy as a clam, Harvey thought. A very voluble clam equipped with Texas Instruments’ latest pocket marvel.

  “What do you like for the density of hot fudge?” Sharps asked.

  “Call it point nine,” Forrester said.

  “Haven’t any of you made fudge?” Charlene demanded. “It doesn’t float. You test it by dripping it into a cup of cold water. Or at least my mother did.”

  “Say one point two, then,” Forrester said.

  “Another billion and a half tons of hot fudge,” Sharps said. Behind him Hamner made more strangled noises.

  “I think we can ignore the rocks,” Sharps said. “Do you see why, now?”

  “Lord God, yes,” Harvey said. He looked at the camera with a start. “Uh, yes, Dr. Sharps, it certainly makes sense to ignore the rocks.”

  “You’re not going to show this, are you?” Tim Hamner sounded indignant.

  “You’re saying no?” Harvey asked.

  “No… no…” Hamner doubled over and giggled.

  ’Now, she’s coming at cometary speeds. Fast. Let’s see, parabolic speed at Earth orbit is what, Dan?”

  “Twenty-nine point seven kilometers per second. Times square root of two.”

  “Forty-two kilometers a second,” Sharps announced. “And we’ve got Earth’s orbital velocity to add. Depends on the geometry of the strike. Shall we say fifty kilometers a second as a reasonable closing velocity?”

  “Sounds good,” Forrester said. “Meteors go from twenty to maybe seventy. It’s reasonable.”

  “Right. Call it fifty. Square that, times a half. Times mass in grams. Bit over two times ten to the twenty-eight ergs. That’s for the vanilla ice cream. Now we can figure that most of the hot fudge boiled away, but understand, Harvey, at those speeds we’re just not in the atmosphere very long. If we come in straight it’s two seconds flat! Anyway, whatever mass you burn up, a lot of the energy just gets transferred to the earth’s heat balance. That’s a spectacular explosion all by itself. We’ll figure twenty percent of the hot-fudge energy transfers to Earth, and” — more buttons pressed, and dramatic rise in voice — “our grand total is two point seven times ten to the twenty-eighth ergs. Okay, that’s your strike.”

  “Doesn’t mean much to me,” Harvey said. “It sounds like a big number…”

  “One followed by twenty-eight zeros,” Mark muttered.

  “Six hundred and forty thousand megatons, near enough,” Dan Forrester said gently. “It is a big number.”

  “Good God, pasteurized planet,” Mark said.

  “Not quite.” Forrester had his own calculator out of the belt case. “About three thousand Krakatoas. Or three hundred Thera explosions, if they’re right about Thera.”

  “Thera?” Harvey asked.

  “Volcano in the Mediterranean,” Mark said. “Bronze Age. Where the Atlantis legend comes from.”

  “Your friend’s right,” Sharps said. “I’m not sure about the energy, though. Look at it this way. All of mankind uses about ten to the twenty-ninth ergs in a year. That’s everything: electric power, coal, nuclear energy, burning buffalo chips, cars — you name it. So our hot fudge sundae pops in with about thirty percent of the world’s annual energy budget.”

  “Um. Not so bad, then,” Harvey said.

  “Not so bad. Not so bad as what? A year’s energy in one minute,” Sharps said. “It probably hits water. If it hits land, it’s tough for anyone under it, but most of the energy radiates back out to space fairly quickly. But if it hits water, it vaporizes it. Let’s see, ergs to calories… damn. I don’t have that on my gadget.”

  “I do,” Forrester said. “The strike would vaporize about sixty million cubic kilometers of water. Or fifty billion acrefeet, if you like that. Enough to cover the entire U.S.A. with two hundred and twelve feet of water.”

  “All right,” Sharps said. “So sixty million cubic kilometers of water go into the atmosphere. Harvey, it’s going to rain. A lot of that water is moving across polar areas. It freezes, falls as snow. Glaciers form fast… slide south… yeah. Harvey, the historians believe the Thera explosion changed the world’s climate. We know that Tamboura, about as powerful as Krakatoa, caused what historians of the last century called ‘the year without a summer’. Famine. Crop failure. Our hot fudge sundae will probably trigger an ice age. All those clouds. Clouds reflect heat. Less sunlight gets to Earth. Snow reflects heat too. Still less sunlight. It gets colder. More snow falls. Glaciers move south because they don’t melt as fast. Positive feedback.”

  It had all turned dead serious. Harvey asked, “But what stops ice ages?”

  Forrester and Sharps
shrugged in unison.

  “So,” Hamner said, “my comet’s going to bring about an ice age?” Now you could see the long lugubrious face of his grandfather, who could look bereaved at a $60,000 funeral.

  Forrester said, “No, that was hot fudge sundae we were talking about. Um — the Hammer is bigger.”

  “Hamner-Brown. How much bigger?”

  Forrester made an uncertain gesture. “Ten times?”

  “Yes,” said Harvey. There were pictures in his mind. Glaciers marched south across fields and forests, across vegetation already killed by snow. Down across North America into California, across Europe to the Alps and Pyrenees. Winter after winter, each colder, each colder than the Great Freeze of ’76–’77. And hell, they hadn’t even mentioned the tidal waves. “But a comet won’t be as dense as a cubic mile of h-h-h—”

  It was just one of those things. Harvey leaned back in his chair and belly-laughed, because there was just no way he could say it.

  Later he made his own tape, alone, in a studio approximation of an office — fake books on the shelves, worn carpet on the floor. Here he could talk.

  “Sorry about that.” (This would run just after one of Harvey’s breakups. He’d done that several times in the Sharps interview.) “The points to remember are these. First, the odds against any solid part of Hamner-Brown hitting us are literally astronomical. Over these distances even the Devil himself couldn’t hit a target as small as Earth. Second, if it did hit, it would probably be as several large masses. Some of those would hit ocean. Others would hit land, where the damage would be local. But if Hamner-Brown did strike the Earth, it would he as if the Devil had struck with an enormous hammer, repeatedly.”

  April: Interludes

  Fifty thousand years ago in Arizona:

  Friction with the air makes the surface incandescent as the oxygen in the atmosphere blowtorches the iron. From this great flying mass, sputtering chunks as large as houses fly of’ as the meteoroid, travelling at a low angle, nears the ground. A huge cylinder of superheated air is forced along by the meteoroid and, as it strikes, this air is forced across the surrounding countryside in a fiery blast that instantaneously scorches every living thing for a hundred miles in every direction.