The number 551 is interesting because it's the product of two prime numbers, 19 and 29. One of the most basic SETI maneuvers was to make up a message with (in this case) 551 ones and zeros, which you could transmit with dots and dashes, then represent them in a crossword-puzzle-style matrix, either 19 squares by 29 or 29 by 19, making a picture out of the black and white squares.

  The signal went like this:

  * * * *

  11110000111010110011001000010000 010101100100000100101001111110 0000010101000100000000111010100011 00000000000000000000000000000000 0000010000000001001000000 0000000000100100001001011100001111000 00000000000100100001001000000100100000 0000000000000000000110001000000000000011 0000000000000000000000001000000000001 100000000000000000110000000100000000000 00000000010101000110000000001010100000000 0000001111101011010111011111111110000000000 0111110100000001110010101000000000001001010 10001011100010000010000101010001000111 000010101000000010100001011100000001110100

  * * * *

  The first time the Chilean astronomer tried, he used the 19 by 29 matrix, and got nothing coherent. The 29 by 19 gave an interesting picture....

  Humans and Martians gathered together in front of the monitor as the Chilean's drawing came in.

  "In English?" Oz said. "What the hell is ‘O Sin'?"

  "I think it's some kind of human joke," Sunrise said. "They said it was 551 ones and zeros?"

  "Correct," Dargo said.

  "Unless it's a coincidence, unlikely, then it's a joke reference to the first example of trying to communicate this way. Frank Drake made it up in 1961, and it was widely broadcast. The O in the upper left corner would be the Sun, with the Solar System underneath it: four little planets, including yours and ours, then two big ones, and then two medium sized."

  "So what about sin?" Oz said.

  "I don't know," Sunrise said. "I don't really understand human jokes. That corner of Drake's picture was a symbolic representation of the atoms of carbon and oxygen. Necessary for life."

  "Silicon and nitrogen," Paul said. "Si and N. They're a silicon-based life-form?"

  "With six legs," Oz said, "or eight, two of them small. There's a square next to the Earth, with a line pointing to a man-shaped diagram. Another square next to Mars, and one over Neptune, with lines toward the diagram of an eight-legged creature."

  "We don't look like that," Sunrise said. "We don't have eight legs."

  "We have eight appendages." Red tapped the screen. "There is a solid line from Neptune to the creature, but only a dotted line from Mars to it. That might mean something."

  "But hold it," Oz said. "Nothing could live on Neptune. Eight legs or nine or whatever. It's a cryogenic hell."

  "No." Red shook his huge head. "Ha, ha. I mean, yes, humans and Martians would freeze solid there in a matter of seconds. But there could be something like organic chemistry with silicon and nitrogen—liquid nitrogen being a solute, like water in our chemistry. You could have compounds analogous to amino acids and proteins. So complex life chemistry could be theoretically possible."

  "There's hardly any free nitrogen on Neptune," Paul said. "Hydrogen, helium, a little methane for color."

  "Not Neptune itself." Red drummed the fingers of his small hands together. "Its largest moon, Triton."

  Paul nodded slowly. "Yeah. Geysers of liquid nitrogen when it's warm enough."

  "We don't know much about it, do we?" Oz said.

  "Haven't been there since forever," Paul said. "A flyby in the nineteen-eighties?"

  "In 1989," Red said. "The Chinese-Japanese Outer Planets Initiative was launched in 2027 but went silent when it arrived in 2044. But there's been a lot of study from various hubbles. There are probably a hundred specialists about to start bouncing off the walls."

  "What about the number down in the corner?" I said.

  "Ten to the seventh," Paul said; "ten million. And that looks like a ‘d’ after it. Ten million days?"

  Red and Snowbird translated it simultaneously. "27,378 years." Snowbird added, "14,970 ares, in Martian sols."

  "I wonder if that's how long you've been on Mars," I said. Red shrugged.

  "It's how long human beings have been all human," Oz said, "in a manner of speaking. Interesting coincidence. The last Neanderthals died about 27,000 years ago. I guess Homo sapiens has been the dominant species ever since."

  "Having killed off the Neanderthals?" Moonboy said.

  Red gave his slightly maddening monotone laugh. "Ha ha. Nobody knows what became of them."

  "Homo sapiens invited them over for lunch," Moonboy said, "and they turned out to be the main course." Dargo shot him a look.

  Oz tapped the eight-legged figure. "These could be your Others. Who created you in their image, more or less."

  "Living that close." Red shook his head. "And on so small a world? Triton isn't even as big as your Moon."

  "They might be like you," I said. "You don't take up a lot of real estate."

  There was a double-ping signal and a familiar face appeared, superimposed over the Drake diagram. Ishan Jhangiani, Science Coordinator on the Earth side. "This is interesting. Some of the Martians were watching the broadcast, but only the yellow ones were affected. And the nine yellow ones who were doing something else were not affected.

  "I don't think we have any organs that discriminate between regular light and coherent light," Red said. "So how could that work?"

  Ishan chewed his lip and nodded. "Well, just pursuing logic ... you would never encounter such a strong burst of coherent light in the normal course of things. So you, or rather the yellow ones, could have such an organ and never know it."

  "But it wouldn't have any useful function," Oz said.

  "Ha ha. But it would. It would make you fall down and speak in tongues whenever somebody on Neptune, or Triton, wanted you to."

  That would turn out to be pretty accurate.

  5

  Unveiled Threat

  After the excitement died down, most of us went back to the mess and zapped up a meal. Dargo went off somewhere to stick pins in dolls.

  I traded the lump of rice in my chicken for the pile of mashed potatoes that came with Oz's meat loaf. He exercises as much as I do, as we all do, but he keeps putting on weight, while I lose it.

  "I don't get it," Moonboy said. "If they wanted to send a dot-and-dash message, why be so roundabout? Why not just use the ruby laser itself?"

  "For some reason they wanted the Martians involved," I said. "One Martian, at least. What I want to know is how Fly-in-Amber got all that information out of the red light." So far, all we'd gotten was on/off, on/off.

  Oz nodded. "And what's different about Fly-in-Amber and those other yellow ones, that they were the only Martians affected by it? The anatomical scans we did on Mars didn't show any significant differences between the various families, except for Red. With all his extra brain and nervous system mass and complexity, I'd expect him to be the one singled out, if any."

  "He said he didn't feel anything special," Meryl said. "But he only looked at it for a couple of seconds. Then he was worrying after Fly-in-Amber."

  "I'll do a high-resolution PET scan of all their eyes and brains," Oz said. "See whether Fly-in-Amber has some anomaly."

  There was a pause and Paul shook his head. "Triton? How could intelligent life evolve on Triton? How could anything complex?"

  Oz studied his meat loaf for clues. "Well, it couldn't be like Earth. A large variety of species competing for ecological niches. At least intuitively that doesn't sound likely. If it's like Red suggested, a quasi-organic chemistry based on silicon and liquid nitrogen, think of how slow chemical reactions would be."

  "And how little chemical variety," Moonboy said, "with so little solar energy pumping it."

  "There's also energy from radioactivity," Paul pointed out, "and tidal friction from Neptune. I think that's what causes the liquid nitrogen geysers they see."

  Moonboy persisted. "But it would never have anything like the variety and energy in the Earth'
s primordial soup."

  "You're all barking up the wrong tree," I said. "If the signal really is coming from the Others, they didn't evolve on Triton. The Martians’ tradition is that they live light-years away. So this laser thing could just be an automated device. It isn't any more or less impossible than the Martian city. That was supposedly built by the Others, a zillion years ago."

  "Or 27,000," Oz said. "You're right. But why did it start blinking exactly as soon as one of the yellow family reached Earth orbit? That would be some sophisticated automation."

  That gave me a little chill. "In other words ... we're being watched?"

  He stroked his beard. "Give me another explanation."

  * * * *

  Over the next several days, scientists on Earth as well as here analyzed the signal from Neptune, which had stopped eight hours and twenty minutes after Fly-in-Amber's condition had been broadcast to Earth. That was exactly twice the travel time of that broadcast to Neptune, which fact was an interesting piece of information in itself. Mission accomplished; turn it off.

  The laser beam was apparently just that, a simple powerful beam of unmodulated coherent light, carrying no information other than the intriguing fact of its own existence.

  There are some natural sources of cosmic radiation that produce coherent light, but nobody was pursuing that direction, since the timing of it would be an impossible coincidence. It was artificial, and in its way was as much a message as the Drake diagram that came out of the amplitude-modulation part of Fly-in-Amber's utterances. The amount of power it was pumping was part of the message, a scary part.

  It could destroy an approaching space ship. Maybe it had, once.

  The frequency-modulation part of the message resisted analysis. Each of the ten iterations of the signal had different and apparently random patterns. The Martians here and on Mars listened to them and agreed that they sounded like Martian speech, albeit in monotone, but made absolutely no sense. Fly-in-Amber found it quite maddening. He said, "It sounds like a human idiot going ‘la la la la’ over and over." Well, maybe. But sometimes the "la" became "la-a-a" or just "ll," and sometimes it sounded like a pencil sharpener trying to say "la."

  Four or five days after the excitement, I was dragging my weary bones home after exercise and was surprised to meet Red at the end of the corridor. The Martians didn't often wander over this way.

  "Carmen. We always meet at my place. Could I have a look at yours?"

  "Sure, why not?" It was a mess, but I doubted that Red would care. He'd learn more.

  I thumbed the lock. "I normally take a shower after working out."

  "Your smell is not toxic." I guess you take your compliments where you can find them.

  He looked large in my small room, and strange, hemmed in by undersized furniture he couldn't use. He wheeled the desk chair over in front of him.

  "Could we have some music? Bach Concerto Number 1 in F Major?"

  "Brandenburg, sure." Pretty loud. I asked the machine and it started.

  "A little louder?" He gestured for me to sit in front of him. I did and he leaned forward and spoke in a barely audible whisper.

  "Everything I do in my quarters is recorded for science. But this must be a secret between you and me. No other humans, no other Martians."

  "All right. I promise."

  "When I listened to the frequency modulation part, I understood it immediately. Only I could understand it."

  "Only you ... it was in your private language? The leader language?"

  He nodded. "Perhaps it is the real reason we have to learn the language. Because this was going to happen eventually."

  His voice became even lower, and I strained to hear. "It told me that we Martians are biological machines, developed for this purpose: to communicate with humans if and when they developed to this point, a time when flight to the stars became possible."

  "I thought it wasn't yet."

  "Within a few human life spans. The Others work slowly."

  "You mean the Others actually did evolve on Triton?"

  "Not at all, no. They do come from a planet revolving around another star, some twenty light-years from here. It's a cold planet, ancient, and its cryogenic kind of life has been there for literally billions of years.

  "The one individual on Triton was especially engineered for its task, as were all of us Martians. We're all here to keep an eye on you humans.

  "The Others move very slowly; their metabolism is glacial. They think fast, faster than you and me, because their mental processes utilize superconductivity. But in physical manipulation of their environment ... you would have to study one for hours to see that it had moved.

  "The one on Triton moves about sixty four times as fast as they do; we move about four times as fast as it does. To match you.

  "They offer this as an analogy. Suppose you humans, for some reason, had to communicate with a mayfly."

  "That's a kind of insect?"

  "Yes. Though it lives most of its life as a variety of nymph. When it becomes an actual insect, it only lives for a day. How would you go about communicating with it?"

  "You couldn't. It wouldn't have anything like a brain or language."

  Red grabbed his head and shook it. "Ha ha. But this is analogy, not science. Suppose it had a quick squeaky language, and intelligence, and civilization, but it lived so fast that the span from birth to death was only one day. How would you communicate with it?"

  "I see what you're driving at. We're the mayflies."

  He grabbed his head again. "You gave away the ending. But suppose you did have to communicate with these intelligent mayflies. To them, you are slow as Sequoias. How do you get them to realize that you are also an intelligent form of life?"

  "Build a machine? One that moves as fast as they do?"

  "Yes, but not in one step. What the Others did was build a machine, a carbon-based biological one, that lived somewhat faster than they did—and which had the ability to build a machine faster than itself. And so on down the line."

  "Until you had one that could talk to mayflies. Humans, in this case."

  He nodded. "That's what we are. We Martians."

  "Your only function is to communicate with us?

  "I would say ‘destiny’ rather than function. We do have a life, a culture, independent of you. But humans are our reason for being."

  "So why," I whispered, waving my hand at the music, "why all the secrecy?"

  "Because I'm not supposed to be explaining this to you. To anybody."

  "We're supposed to decode the message ourselves?"

  "I don't think you could. I don't think even a Martian could, no matter how brilliant, unless he spent all his youth studying my language."

  "Maybe not even then," I said. "Oz says your brain is immensely more complex than other Martians'. But why do the Others want to keep it secret?"

  "I don't know the details yet. But they're afraid of you; of what you may become. Millions of years ago, they had trouble with a planet in a nearby system, somewhat like the Earth. Water-carbon-oxygen life. They're frightened by how fast you act. How fast you evolve."

  "What kind of trouble did they have with this planet? A war?"

  "I don't think that would be possible. I think it was what you would call a pre-emptive strike."

  "So ... they destroyed them?"

  Red nodded slowly. "After the young planet started sending out interstellar probes. The Others’ world was relatively near—their sun was maybe a hundred times the distance from here to Neptune—what we would call a wide double-star system—so of course the Others were their first interstellar destination."

  "The young world was going to invade at that distance?"

  "The Others didn't know. But there were wars on the oxygen planet, worldwide wars, for years before they had space travel, and the Others could observe them indirectly. As we, and they, have done with you."

  "So the Others suddenly developed space travel themselves, and went off to do this ??
?preemptive strike'?"

  "Oh, no. They'd been exploring other planets with probes for many thousands of years. They'd been to this solar system, and others, with complex autonomous robots to gather information, deliver it, and self-destruct."

  His voice grew even lower. "As we have observed, they have considerable talent, power, for manipulating things at great distances. The tools for the pre-emptive strike were in place long before they decided they had to be used."

  "My god. Are they in place here on Earth, too?"

  "That wasn't clear. Sometimes the message was allusive, metaphorical ... it was sort of ‘if it's true, it's too late for the humans to do anything about it; if not, nothing needs to be done.’"

  "We might feel differently. We humans."

  "It also said that for the humans’ sake, the threat ought to be kept secret. Not for its own protection, it emphasized. For your sake—I think so it wouldn't have to take action prematurely. Though my sense is the ‘action’ wouldn't be anything like an invasion or even a launched missile. It would be a small act, like turning on the laser beacon.

  My heart was hammering. "Could it destroy the Earth just like that? So casually?"

  "I doubt it. And it wouldn't want to, literally, destroy the Earth. It said that we could have the planet if you proved unsuitable. We Martians."

  "Now that would go down really well on Earth."

  "Don't worry. Who needs the gravity? The Others are aquatic, or whatever you call something that lives in liquid nitrogen. They don't think about gravity any more than fish do. They just float there."

  I felt he was telling the truth. "You're on our side."

  He nodded. "It can't see that. Even if I was not in beghnim with you, I would feel closer to you, to all humans, than to them. The Others may be our creators, but in terms of simple existence, we are much closer to you.

  "They hardly live at all, on our time scale ... and technically, they never die."

  "Never? How do they manage that?"

  "An individual will stop moving, stop metabolizing, for a thousand years or more. Dead except for the information structures that make up its individuality. When it's needed again, it's kind of ... jump-started."