The Ringworld Engineers

after.

Presently she took him to the water bed — ignoring the presence of Kawaresksenjajok, who grinned at them over his shoulder, once, then went back to watching the Great Ocean move past.

In rishathra there was reassurance. Spurious, perhaps. Who cared?

There sure was a lot of water down there.

From a thousand miles up, one could see a long way before the blanket of air blocked the view. And for most of that distance, there wasn’t a single island! The contours of sea bottom showed, and some of that was shallow enough. But the only islands were far behind, and those had probably been underwater peaks before Fist-of-God distorted the land.

There were storms. One looked in vain for the spiral patterns that meant hurricane and typhoon. But there were cloud patterns that looked like rivers in the air. As you watched them, they moved: even from this height, they moved.

The kzinti who dared that vastness had not been cowards, and those who returned had not been fools. That pattern of islands on the starboard horizon — you had to squint to be sure it was really there — must be the Map of Earth. And it was lost in all that blue.

A cool, precise contralto voice eased into his thoughts. “Louis? I have reduced our maximum velocity to four miles per second.”

“Okay.” Four, five — who cared?

“Louis, where did you say the meteor defense was located?”

Something in the puppeteer’s tone… ”I didn’t say. I don’t know.”

“The shadow squares, you said. You’re on record. It must be the shadow squares if the meteor defense can’t guard the Ringworld’s underside.” No overtones, no emotion showing in that voice.

“Do I gather I was wrong?”

“Now, pay attention, Louis. As we passed four point four miles per second, the sun flared. I have it on visual record. We didn’t see it because of the flare shielding. The sun extruded a jet of plasma some millions of miles long. It is difficult to observe because it came straight at us. It did not arch over in the sun’s magnetic field, as flares commonly do.”

“That was no solar flare that hit us.”

“The flare stretched out several million miles over a period of twenty minutes. Then it lased in violet.”

“Oh my God.”

“A gas laser on a very large scale. The earth still glows where the beam fell. I estimate that it covered a region ten kilometers across: not an especially tight beam, but it would not normally need to be. With even moderate efficiency, a flare that large would power a gas laser beam at three times ten to the twenty-seventh power ergs per second, for on the order of an hour.”

Silence.

“Louis?”

“Give me a minute. Hindmost, that is one impressive weapon.” It hit him, then: the secret of the Ringworld engineers. “That’s why they felt safe. That’s why they could build a Ringworld. They could hold off any kind of invasion. They had a laser weapon bigger than worlds, bigger than the Earth-Moon system, bigger than… Hindmost? I think I’m going to faint.”

“Louis, we don’t have time for that.”

“What caused it? Something caused the sun to jet plasma. Magnetic, it has to be magnetic. Could it be one function of the shadow squares?”

“I wouldn’t think so. Cameras record that the shadow square ring moved aside to allow the beam to pass, and constricted elsewhere, presumably to protect the land from increased insolation. We cannot assume that this same shadow-square ring was manipulating the photosphere magnetically. An intelligent engineer would design two separate systems.”

“You’re right. Absolutely right. Check it anyway, will you? We’ve recorded all possible magnetic effects from three different angles. Find out what made the sun flare.” Allah, Kdapt, Brahma, Finagle, let it be the shadow squares! “Hindmost? Whatever you find, don’t curl up on me.”

There was a peculiar pause. Then “Under the circumstances, that would doom us all. I would not do that unless there was no hope left. What are you thinking?”

“There is never no hope left. Remember.”

The Map of Mars was in view at last. It was farther away than the Map of Earth — a hundred thousand miles straight to starboard — but unlike the Map of Earth, it was one compact mass. From this angle it showed as a black line: twenty miles above the sea, as the Hindmost had predicted.

A red light blinked on the lander’s instrument board. Temperature: a hundred and ten Fahrenheit, just right for a spa. No lights blinked on the big coffin that held Chmeee. The autodoc had its own temperature controls.

The kzinti defenders seemed to have run out of explosives. Their supply of firewood seemed infinite.

Twenty thousand miles to go, at four miles per second.

“Louis?”

Louis eased himself out of the sleeping field. The Hindmost, he thought, looked awful. Mane rumpled, the garnets rubbed off along one side. He staggered as if his knees were made of wood.

“We’ll think of something else,” Louis told him. He was wishing he could reach through the wall, stroke the puppeteer’s mane, give reassurance of some kind. “Maybe there’s some kind of library in that castle. Maybe Chmeee already knows something we don’t. Tanj, maybe the repair crew already knows the answer.”

“We know the same answer. A chance to study sunspots from underneath.” The puppeteer’s voice was wintry-cool, the voice of a computer. “You guessed, didn’t you? Hexagonal patterns of superconductor embedded in the Ringworld floor. The scrith can be magnetized to manipulate plasma jets in the solar photosphere.”

“Yah.”

“It may have been just such an event that pushed the Ringworld off center. A plasma jet formed to fire on a meteoroid, a stray comet, even a fleet from Earth or Kzin. The plasma impacted the Ringworld. There were no attitude jets to push it back into place. Without the plasma jet, the meteor itself might have been sufficient. The repair crew came later: too late.”

“Let’s hope not.”

“The grid is not a backup for the attitude jets.”

“No. Are you all right?”

“No.”

“What are you going to do?”

“I will follow orders.”

“Good.”

“If I were still Hindmost to this expedition, I would give up now.”

“I believe you.”

“Have you guessed the worst of it? I compute that the sun can probably be moved. The sun can be made to jet plasma, and the plasma can be made to act as a gas laser, forming a photon drive for the sun itself. The Ringworld would be pulled along by the sun’s gravity. But even the maximum thrust would be minuscule, too little to help us. At anything over two times ten to the minus fourth power gravities of acceleration, the Ringworld would be left behind. In any case, radiation from the plasma jet would ruin the ecology. Louis, are you laughing?”

Louis was. “I never thought of moving the sun. I never would have. You actually went ahead and worked out the math?”

Wintry-cool and mechanical, that voice. “I did. It can’t help us. What is left?”

“Follow orders. Hold us at four miles per second antispinward. Let me know when I can flick across to the lander.”

“Aye, aye.” The puppeteer turned away.

“Hindmost?”

A head turned back.

“Sometimes there’s no point in giving up.”