Encounter with Tiber [v1.0]

by By Buzz Aldrin

  It was bizarre in many ways. For decades, dedicated amateur radio astronomers, and interested professionals who could squeeze in the time on the big dishes, had been trying to find something, anything, that might look like a signal from another civilization. The prevalent idea had been that most likely, if we found it, it would not be a direct attempt to communicate with us, but a general announcement to the universe, perhaps as a beacon aimed at likely stars. Since they wouldn’t be trying to reach us in particular, all the astronomers who had thought about the problem had thought that we would need extremely sensitive detectors and big antennas to hear an alien civilization at all.

  Now, years after many of the SETI (Search for Extraterrestrial Intelligence) projects had been shut down for lack of funds, and the rest had struggled to get equipment sensitive enough to pick up faint signals from planets that might be hundreds of light-years away, suddenly here was a loud, clear signal coming in from the nearest star, something that almost anyone could get with even the crudest backyard receivers—and yet transmitted on the least convenient, most noise-prone wavelength imaginable.

  At last the analysis program passed its checkouts, and Chris told it to try the data. The program opened the file that contained the signal strengths and antenna positions, loaded the data into the appropriate internal matrix, and began processing. Various short messages indicating that the program had completed another step popped up on the screen; the program was executing properly.

  It finished, and displayed a set of equations plus the message “UNIQUE SOLUTION, 95% CERTAIN”-indicating that there was only one mathematically possible result to explain the data, and that the odds were nineteen to one or better that the solution was right.

  “Now, that’s weird,” François said, peering over Chris’s shoulder. “That looks like—er—”

  “It looks like it can’t possibly be an orbit around either star, or around their combined center of mass, or around any of their Lagrange points,” Chris finished for him. “Yes, I know.”

  “But the curve is beautifully smooth,” François pointed out. “It doesn’t look like garbage or error, it looks like—”

  Jiro too came over to kibbitz. “Hmm. Suppose you’re not dealing with one mass but two,” he said. “Suppose it’s a small body orbiting a larger body orbiting one of the stars. If you figure that—”

  “You’re right,” Chris said, and rapidly keyed in a test sequence. The program ran for several long minutes as it tried and discarded dozens of alternatives. Then quite suddenly, an animated display popped up on the screen, showing dots labeled A and B circling each other like wary boxers—and a strange lozenge-shaped spiral circling B.

  “Yep,” Chris said. “That’s a body in a highly elliptical orbit around another much larger body, which is orbiting B. Seems like a strange place for life, but that’s too good a picture not to be right.” He tapped the keys a few times, and said, “Well, if you figure that the planet is a gas giant, like Jupiter or Saturn, then an Earthlike planet in that kind of orbit around it would be marginally habitable—usually. It would get mighty cold on the long swings outward, and pretty hot whenever it swung in toward Alpha Centauri B. The real problem is, just guessing at it, I don’t think a moon around a gas giant could be stable in that position over a period of billions of years.”

  Jiro’s hands went to the keys. “Want to see if we can modify it to estimate a position and mass for the gas giant, and then check long-term stability on that elliptical orbit?”

  “Absolutely,” Chris said. “Funny thing, but that’s gravity for you—we can figure out exactly the mass of the planet, but we have no way of knowing whether what’s orbiting it is the size of a Volkswagen or the size of the Earth. The mass of the orbiting body doesn’t affect the period of the orbit, only the mass of the central body.”

  Jiro shrugged. “Just the way it works out. Well, our results do seem to be consistent. That central body seems to be about one hundred forty Earth masses—or one and a half times as big as Saturn, or less than half as big as Jupiter. Call it either a super-Saturn or a mini-Jupiter, eh?”

  Mission Control, seeing the importance of the results, authorized Jiro, François, and Chris to spend another two hours on the problem of the stability of the orbiting body, from which the broadcast was coming.

  At one time it was thought that all the planets in the solar system must be moving in exactly the same fashion every year, because it was assumed that even a slight annual change would accumulate until the planet was in a drastically different orbit, and sooner or later would accumulate so far that the planet would fall into the Sun, or swing far enough out to be lost forever, or eventually drift into an orbit that did repeat over time.

  But in the late 1980s, chaos theory—the mathematics that governs situations where a small difference at the beginning could have large and unpredictable effects at the end—brought astronomers to the realization that although each planet’s orbit was generally similar to the one from the year before, some of the planets and moons—especially in the more eccentric orbits, or in orbits far from the Sun (like Pluto’s)—could have chaotic orbits that never replicated perfectly but nevertheless kept the body in orbit for hundreds of millions of years. An orbit was “stable,” therefore, if the equations that described it would regularly return to the same sequence of values, so that the motion of the body would repeat, over and over. It was “unstable” if that never happened, and in that latter case, the more unstable (that is, the farther away from ever returning to the same place at the same speed moving in the same direction), the less likely it was to have lasted in its orbit for very long.

  The answer checked out but was highly unsatisfactory. “Well,” Chris said, “I guess what we’ve done is solved half the mystery. It couldn’t have been there much longer than forty million years. Therefore life didn’t evolve there; whoever and whatever they are, they aren’t from that moon. That’s almost reassuring, since a body with that orbit would be a hell of a place for habitability on a long-term basis. We must be getting transmissions from a beacon or something. Maybe it’s a distress call from an alien ship that was forced to land there, or a scientific probe reporting back what it’s found, or—”

  François looked up from the neighboring screen and said, “Not likely.”

  Chris stopped and said, “Why not?”

  “Because if you remember, one assumption we had to start with was that the signal was of constant strength; so I was rechecking that assumption against the computed orbit. And in one sense it is of constant strength—it’s all coming at the same power. But there’s been a very slow secular increase in signal strength going on, which is perfectly explained if you assume that we’re moving into the center of a beam. Which makes sense—even with a very large aperture, and a highly collimated beam, at that wavelength beam spread should work out to six or seven astronomical units either way from the Sun. You couldn’t point it directly at the Earth, perhaps, or there was no point in it—but if you pointed it at the Sun, the Earth would never be outside the beam.”

  Jiro and Chris gaped at him, and then Chris said what was obvious. “So they aren’t broadcasting to the whole universe. Whoever or whatever they are, they aimed that message right at us.”

  * * * *

  6

  AT THE END OF THE NEXT WORK PERIOD, WHEN A GROUP MEAL WAS scheduled, Tatiana Haldin said, “Well, congratulations; thanks to publication on the Internet, the three of you are now famous, and the rest of us will be wanting your autographs. You might be interested to know that the International Astronomical Union has already scheduled a meeting to name the gas giant that Dr. Terence has identified orbiting Alpha Centauri B.”

  “We don’t even know that it’s a gas giant,” Chris said, “and you can call me Chris. All we know is that it masses about a hundred and forty times what the Earth does. That’s not a lot to go on.”

  Denisov snorted. “And what else is a planet that big going to be made of? It’s big enough to have
retained almost all its primordial hydrogen and helium, and since they make up the majority of matter in the universe, what else do you think it might be made of? Chocolate ice cream? And you should tell him, Tatiana, about the campaign back in his country.”

  “I didn’t wish to embarrass him,” Haldin said mildly.

  “Well, I’ve always enjoyed embarrassing him,” Lori said, grinning. “Chris, there’s a bunch of nuts back home writing to Congress who want to name that gas giant after you. They’re calling themselves the Beta Centauri Terence Society.”

  Chris groaned. “How many different ways can the same people be dumb? In the first place, all of us had a hand in the discovery. And secondly, the star is Alpha Centauri B—the second largest star in the double star Alpha Centauri. Beta Centauri is a completely different star, in a different part of the constellation Centaurus, a lot farther away, just in sort of the same direction. And anyway, naming that planet, if that’s what it is, is the job of the International Astronomical Union. God, if you leave that kind of thing to the vote of the people, someday we’ll have planets named after Elvis and Cher.”

  Everyone laughed; Tatiana said, “I’m sure the new planet won’t have a name for a long time. The IAU is at least as political as any other scientific body; they’ll have to argue about whether to continue naming planets after gods, and if so, whose gods, and if whose, which of their gods, and so forth indefinitely.”

  François nodded. “If anyone asks me, I shall suggest ‘Marianne.’”

  “Is there something especially French about a gas giant around Alpha Centauri B?” Lori asked, curiously.

  “No, I don’t mean after the spirit of the Republic. I like it because that’s my daughter’s name. It’s as good a reason as any other. But I do think our station commander is right; unless we suddenly have a way of finding thousands or millions of planets, everyone will want the new planet to be named after their particular god or cause, and the IAU probably won’t get to talk about much else until it’s finally settled—if it ever is. Meanwhile, I do believe Jiro has something to show us.”

  The Japanese astronaut smiled shyly. “I’d like François to begin. His insight led me to my results.”

  François, who had gotten that information from his friends at CNRS, began, “First of all, the burst of base eight numbers are coming in groups of 16,769,021, with a longer break between each group. And what makes that interesting is that some bright people ran it through a simple factoring program and discovered that it’s equal to 4093 times 4097—two prime numbers.”

  “Uh, excuse my being dumb, but this means . . . ?” Lori asked.

  “Since a prime number isn’t evenly divisible by any other number, if you’re transmitting a grid-type pattern—say a picture or a chart—and its size is the product of two primes, then there are only a couple of possible arrangements for the numbers in the grid. If either number were not prime, there’d be a very large number of possible arrangements, and that would mean you wouldn’t be able to figure out what the picture was a picture of.”

  Chris jumped in. “Like, suppose you know that you’re getting a list of the cells of an individual grid, but you don’t know what shape the grid is— only that they sent you sixty cells. Well, sixty could be the number of cells in a five-by-twelve, or a six-by-ten, or fifteen-by-four, or for that matter a two-by-thirty or a three-by-twenty grid. And if the number were much larger, and the product of many different numbers, you could spend a long time looking for a way to arrange the grid that made sense. But suppose they sent you seventy-seven cells; that can only be a seven-by-eleven grid, or an eleven-by-seven that’s the same grid lying on its side. So what this means is that they’re sending us pictures, tables, charts, something like that—and every picture is four thousand ninety-three by four thousand ninety-seven dots or pixels or whatever.”

  Denisov nodded and said, “And it’s more evidence of their alienness. That’s the first prime greater than four thousand ninety-six times the first prime smaller than four thousand ninety-six—and if you write four thousand ninety-six in base eight, it’s a one followed by four zeros. So it looks like when they laid out their grid, they set it up to come out close to what they would think of as ‘round’ numbers.”

  “Has anyone tried to assemble the pictures yet?” Lori asked.

  “I thought you’d never ask,” Jiro said. “I have a feeling that everywhere on Earth people are showing this to each other, but they don’t quite have the nerve to display it publicly. My guess is that at least a hundred people have tried the same thing I have. After all, the only reason we have a copy of the signal is because we happen to be sitting at the receiving antenna and we sort-of-accidentally happen to be recording it; the ground stations we’re transmitting it to not only have copies, they also have a lot of people who are paid to analyze it—whereas I’m just doing it in my spare time. So I’m sure other people have hit on the solution I have, which is this: suppose we assume that the beeps and honks, as they’re calling them, really do represent binary one and zero, and that therefore the groups of three are base eight numbers. There are really only four possibilities as I see it: either you read the group of three left to right, or right to left, and either you read beep as zero and honk as one, or vice versa. On that basis, for example; ‘beep beep honk’ could mean one, four, six, or three. What occurred to me was this: what if we just make a guess that the numbers represent values of bright and dark on a 4093 by 4097 grid? Then there are actually only eight possible images that each frame might be, and furthermore half of them are black-for-white negatives of the others. Well, then, it wasn’t all that difficult to set up a program to compute an appearance for all 16,384 frames eight times—they do things much more complicated than that in a matter of a few minutes in the new virtual reality games in the arcades, you know, and we have a good deal more computational power available than they do. And then one further idea struck me—now I have these eight sets of frames . . . what could they be? Photographs? A photographic image of a book page, perhaps?

  “The first thing I noted was that quite a few of them in this group” — he clicked on the shared screen and showed the group—”look like kind of an oddly notated star map.”

  “That’s what it is, all right,” Chris said. “Those are the principal pulsars near us, with lines proportional in length to distances to us—or more likely to Alpha Centauri. Unless we have a precise tool for measuring the length of those lines on the screen, the differences aren’t going to matter much in this scale of a picture.”

  Everyone turned to look at him, and he said, “I had something like that on my bedroom wall as a kid—the poster version of the plate that went on our Pioneer spacecraft, way back in the seventies. I fell asleep looking at it, a lot of the time. And that’s so close to the same pattern, that, since in astronomical terms we aren’t very far from Alpha Centauri—”

  “I see,” Jiro said, “Well, then, no doubt a lot of people have figured that one out, too. And perhaps from that we’ll be able to crack their system of numbers and measurements. Certainly there’s something that looks a lot like writing, right next to lines that look like they ought to be dimensions. Anyway, it occurred to me that since several consecutive pictures were pretty similar to each other, there might be a reason for what seemed like a lot of redundancy—I think this is a movie.”

  “A movie?” Lori said. “So each of those sixteen-million-or-so-number sets is a description of a frame?”

  “That was the idea I had,” Jiro said. “And here’s the result: we can only guess at the intended projection speed, at least until we figure something out about their writing, but this looks convincing to me.”

  The screen popped into focus, and they saw eight creatures climbing into what had to be a spacecraft. Two of them seemed to be very tall and thin, covered with fine fur, with big ears like a bat’s. Two others, of the same body shape, were smaller. Two were square-built and strong looking, like gorillas, with strange high ridges that stuck s
traight up from their shoulders and a high, hair-covered crest that rose from the top of their head like a mohawk. Their fur seemed to be thicker, longer, and coarser than that of the taller ones, and very dark; they had thick beards under their jaws, almost like manes. Two others had the same dark and heavy fur and were also squat in build like an ape, though they stood as erect as any human; they were quite short and had no crests or beards.

  As the ISS crew watched, the creatures waved and got into an odd, thick-bodied rocket ship that lay on its side; the rocket floated straight up a long way, and then they saw the engines fire.

  The image cut to a rendezvous with something that looked like a space station in orbit: a torus or ring shape impaled on the end of a column sticking through its center. The little craft docked at the tip near the torus, a quick interior shot showed the alien crew getting into the bigger ship, and then the little craft undocked and went away. Abruptly, on the big structure, the end away from the torus fired a great stream of white-hot stuff into space.

  The first of the crew to speak was Haldin; she said only, “Jiro, I would have to say that if your interpretation isn’t right, it’s the damnedest coincidence in history.”