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This was hardly the right time to ask, though Duncan was tempted.)

Yet, ironically, there was a small conspiracy, in this very room-a conspiracy mutually agreed upon. The Committee had guessed that he now appreciated the significance of the name Argus to Terran security -and he knew that it knew. Each side understood the other perfectly, and the next item of business was quickly adopted.

“So what was Mr. Helmer’s Argus?” asked the woman whom Duncan had tentatively placed up on the Moon. “And can you account for his odd behavior?”

Duncan opened the stained notebook to display 275 that astonishing fall-page sketch which had so transfixed him at its first revelation. Even now that he knew its true scale, he could not think of it as anything except a drawing of a sea urchin. But Diadenta was only thirty or forty centimeters across; Argus would be at least a thousand kilometers in diameter, if Karl’s analysis was right. And of that, Duncan no longer had any doubt, though he could never give his full reasons.

“Karl Helmer had a vision,” he began. “I’ll try to pass it on as best I can, though this is not my field of knowledge. But I knew his psychology, and perhaps I can make you understand what he was trying to do.”

You may be disappointed again, he told himself -you may dismiss the whole concept as a crazy !cientist’s delusion. But you’ll be wrong; this could be infinitely more important than some trivial conspiracy threatening your tidy little world….

“Karl was a scientist, who always hoped to make some great discovery-but never did. Though he was highly imaginative, even his wildest flights were always soundly based on reality. And he was ambitious….”

“If it were so,” murmured a quiet voice from the air beside him, “it was a grievous fault. And grievously hath Caesar answered it. Sorry-please continue

The reference was unfamiliar to Duncan, and he showed his annoyance at the interruption by pausing for a few seconds.

“He was interested in everything-too many things, perhaps-but his great passion was the still unsolved cETi problem—communications with extraterrestrial intelligence. We used to argue about it for hours when we were boys; I could never be quite sure when he was completely serious, but I am now.

“Why have we never detected radio signals from the advanced societies which must surely be out there in space? Karl had many theories, but in the end he settled on the simplest. It’s not original, and I’m sure you’ve heard it before. “We ourselves broadcast radio signals for only

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about a hundred years, roughly spanning the twentieth century. By the end of that time, we’d switched to cable and optical and satellite systems, concentrating all their power where it was needed, and not spilling most of it wastefully to the stars. This may well be true of all civilizations with a technology comparable to ours. They only pollute the universe with indiscriminate radio noise for a century or two-a very brief fraction of their entire history.

“So even if there are millions of advanced societies in this Galaxy, there may be barely a handful just where we were three hundred years ago-still splashing out radio waves in all directions. And the laws of probability make it most unlikely that any of these early electronic cultures will be within detection range; the nearest may be thousands of light-years away.

“But before we abandon the search, we should explore all the possibilities-and there’s one that has never been investigated, because until now there was little we could do about it. For three centuries, we’ve been studying radio waves in the centimeter and meter bands. But we have almost completely ignored the very long waves-tens and hundreds of kilometers in length.

“Now of course there were several good reasons for this neglect. In the first case, it’s impossible to study these waves on Earth-they don’t get through the ionosphere, and so never reach the surface. You have to go into space to observe them.

“But for the very longest waves, it’s no good merely going up to orbit, or to the other side of the Moon, where CYCLOPS n was built. You have to go halfway out to the limits of the Solar System.

“For the Sun has an ionosphere, just like the Earth’s—except that it’s billions of times larger. It absorbs all waves more than ten or twenty kilometers in length. If we want to detect these, we have to go out to

Saturn.

“Such waves have been observed, but only on a few occasions. About forty years ago, a Solar Survey mission picked them up; it wasn’t looking for radio waves at all, but was measuring magnetic fields between Jupiter and

Saturn. It observed pulsations that must have been due to a radio burst at around fifteen kilohertz, corresponding to a wavelength of twenty kilometers. At first it was thought that they came from Jupiter, which is still full of electromagnetic surprises, but that source was eventually ruled out, and the origin is still a mystery.