In response to her typed commands the screen now displayed the disposition of all the radio telescopes.
“It's being received by 116 individual telescopes. Clearly it's not a malfunction in one or two of them. Okay, now we should have plenty of time baseline. Is it moving with the stars? Or could it be some ELINT satellite or aircraft?”
“I can confirm sidereal motion, Dr. Arroway.”
“Okay, that's pretty convincing. It's not down here on Earth, and it probably isn't from an artificial satellite in a Molniya orbit, although we should check that. When you get a chance, Willie, call up NORAD and see what they say about the satellite possibility. If we can exclude satellites, that will leave two possibilities: It's a hoax, or somebody has finally gotten around to sending us a message. Steve, do a manual override. Check a few individual radio telescopes—the signal strength is certainly large enough—and see if there's any chance this is a hoax; you know, a practical joke by someone who wishes to teach us the error of our ways.”
“A handful of other scientists and technicians, alerted on their buzzers by the Argus computer, had gathered around the command console. There were half smiles on their faces. None of them was thinking seriously of a message from another world quite yet, but there was a sense of no-school-today, a break in the tedious routine to which they had become accustomed, and perhaps a faint air of expectation.
“If any of you can think of any other explanation besides extraterrestrial intelligence, I want to hear about it,” she said, acknowledging their presence.
“There's no way it could be Vega, Dr. Arroway. The system's only a few hundred million years old. Its planets are still in the process of forming. There isn't time for intelligent life to have developed there.
It has to be some background star. Or galaxy.”
“But then the transmitter power has to be ridiculously large,” responded a member of the quasar group who had returned to see what was happening. “We need to get going right away on a sensitive proper motion study, so we can see if the radio source moves with Vega.”
“Of course, you're right about the proper motion, Jack,” she said. “But there's another possibility.
Maybe they didn't grow up in the Vega system. Maybe they're just visiting.”
“That's no good either. The system is full of debris. It's a failed solar system or solar system still in its early stages of development. If they stay very long, their spacecraft'll be clobbered.”
“So they only arrived recently. Or they vaporize incoming meteorites. Or they take evasive action if there's a piece of debris on a collision trajectory. Or they're not in the ring plane but in polar orbit, so they minimize their encounters with the debris. There's a million possibilities. But you're absolutely right; we don't have to guess whether the source is in the Vega system. We can actually find out. How long will that proper motion study take? By the way, Steve, this isn't your shift. At least tell Consuela you're going to be late for dinner.”
Willie, who had been talking on the phone at an adjacent console, was displaying a wan smile.
“Well, I got through to a Major Braintree at NORAD. He swears up and down they have nothing that'll give this signal, especially not at nine gigahertz. 'Course, they tell us that every time we call. Anyway, he says they haven't detected any spacecraft at the right ascension and declination of Vega.”
“What about darks?”
By this time there were many “dark” satellites with low radar cross sections, designed to orbit Earth unannounced and undetected until an hour of need. Then they would serve as backups for launch detection or communications in a nuclear war, in case the first-line military satellites dedicated to these purposes were suddenly missing in action. Occasionally a dark would be detected by one of the major astronomical radar systems. All nations would deny that the object belonged to them, and breathless speculation would erupt that an extraterrestrial spacecraft had been detected in Earth orbit. As the Millennium approached, the UFO cults were thriving again.
“Interferometry now rules out a Molniya-type orbit, Dr. Arroway.”
“Better and better. Now let's take a closer look at those moving pulses. Assuming that this is binary arithmetic, has anybody converted it into base ten? Do we know what the sequence of numbers is?
Okay, here, we can do it in our heads… fifty-nine, sixty-one, sixty-seven… seventy-one… Aren't these all prime numbers?”
A little buzz of excitement circulated through the control room. Ellie's own face momentarily revealed a flutter of something deeply felt, but this was quickly replaced by a sobriety, a fear of being carried away, an apprehension about appearing foolish, unscientific.
“Okay, let's see if I can do another quick summary. I'll do it in the simplest language. Please check if I've missed anything. We have an extremely strong, not very monochromatic signal. Immediately outside the bandpass of this signal there are no other frequencies reporting anything besides noise. The signal is linearly polarized, as if it's being broadcast by a radio telescope. The signal is around nine gigahertz, near the minimum in the galactic radio noise background. It's the right kind of frequency for anyone who wants to be heard over a big distance. We've confirmed sidereal motion of the source, so it's moving as if it's up there among the stars and not from some local transmitter. NORAD tells us that they don't detect any satellites— ours or anybody else's—that match the position of this source. Interferometry excludes a source in Earth orbit anyway.
“Steve has now looked at the data outside the automated mode, and it doesn't seem to be a program that somebody with a warped sense of humor put into the computer. The region of the sky we're looking at includes Vega, which is an A-zero main sequence dwarf star. It's not exactly like the Sun, but it's only twenty-six light-years away, and it has the prototype stellar debris ring. There are no known planets, but there certainly could be planets we don't know anything about around Vega. We're setting up a proper motion study to see if the source is well behind our line of sight to Vega, and we should have an answer in— what? — a few weeks if we're restricted on our own, a few hours if we do some long-baseline interferometry.
“Finally, what's being sent seems to be a long sequence of prime numbers, integers that can't be divided by any other number except themselves and one. No astrophysical process is likely to generate prime numbers. So I'd say—we want to be cautious, of course—but I'd say that by every criterion we can lay our hands on, this looks like the real thing.
“But there's a problem with the idea that this is a message from guys who evolved on some planet around Vega, because they would have had to evolve very fast. The entire lifetime of the star is only about four hundred million years. It's an unlikely place for the nearest civilization. So the proper motion study is very important. But I sure would like to check out that hoax possibility some more.”
“Look,” said one of the quasar survey astronomers who had been hovering in the back. He inclined his jaw to the western horizon where a faint pink aura showed unmistakably where the Sun had set. “Vega is going to set in another couple of hours. It's probably already risen in Australia. Can't we call Sydney and get them looking at the same time that we're still seeing it?”
“Good idea. It's only middle afternoon there. And together we'll have enough baseline for the proper motion study. Give me that summary printout, and I'll telefax it to Australia from my office.”
With deliberate composure, Ellie left the assembled group crowded around the consoles and returned to her office. She closed the door very carefully behind her.
“Holy shit!” she whispered.
“Ian Broderick, please. Yes. This is Eleanor Arroway at Project Argus. It's something of an emergency.
Thanks, I'll hold on…. Hello, Ian? It's probably nothing, but we have a bogey here and wonder if you could just check it out for us. It's around nine gigahertz, with a few hundred hertz bandpass. I'm telefaxing the parameters now…. You have a feed good at nine gigahertz already on the dish? That's a bit of luck…. Yes, Vega is smack in the middle of the field of view. And we're getting what looks like prime number pulses….
Really. Okay, I'll hold on.”
She considered again how backward the world astronomical community still was. A joint computer data- basing system was still not on-line. Its value for asynchronous telenetting alone would…
“Listen, Ian, while the telescope finishes slewing, could you set up to look at an amplitude-time plot? Let's call the low-amplitude pulses dots and the high-amplitude pulses dashes. We're getting… Yes that's just the pattern we've been seeing for the last half hour…. Maybe. Well, it's the best candidate in five years, but I keep remembering how badly the Soviets got fooled with that Big Bird satellite incident around 74. Well, the way I understand it, it was a U. S. radar altimetry survey of the Soviet Union for cruise missile guidance…. Yes, a terrain
