Dale nodded.

"So, as I was saying," continued Frank, "Alpha Centauri A is actually damn near a twin for our own sun, Sol. It’s the same color, the same temperature, and so on. And it’s about the same age — actually, a little older. But there’s one significant way in which Centauri A differs from Sol."

"And what’s that?"

"Its brightness. Centauri A is an inherently brighter star — fifty-four percent brighter than our sun."

"So?"

"So even on cloudy days here, all the Tosoks wear those pop-in sunglasses. If they’re from a world of a brighter star, our dimmer sun shouldn’t bother them."

"Maybe they have a different atmosphere from us; maybe it’s not transparent like ours is."

Frank nodded, impressed. "That would be an excellent explanation, except for one thing: the Tosoks breathe our air without any difficulty, and when Clete went aboard their mothership, he breathed their air without trouble, too — and you saw in those videotapes that it was crystal clear."

"Well, then, maybe they orbit their sun farther out than we orbit ours."

They had come to a park bench. Dale motioned for them to sit down.

"Exactly," said Frank, lowering himself to the bench. "In fact, when I was talking to Kelkad about how long it would take to build replacement parts for the mothership, he got upset when I said two years — but he calmed down when Hask explained I meant two Earth years. The Tosok year is obviously much longer, and since Alpha Centauri A is about the same mass and size as Sol, to have a substantially longer year, the Tosok home world must orbit much farther out from it than we do from our sun."

"I don’t know anything about astronomy," said Dale, "but that sounds reasonable."

"Well, it is — sort of. Remember, Centauri A is the same size, but 1.54 times as bright as our sun. A planet orbiting the same distance from Centauri A as Earth is from Sol would therefore get 1.54 times as much light from it."

"Okay."

"But if you double the distance, you only get one quarter of the sunlight.

So, a planet orbiting Centauri A at a distance of two AUs — two times the distance between Earth and Sol — would get one quarter of 1.54 times Sol’s light as seen from Earth. That works out to — let me think — something like forty percent of what we get."

"Well, that would explain why they always need sunglasses, even on cloudy days. But wouldn’t that also make their world much cooler than ours?"

Frank smiled. "For someone who doesn’t know anything about astronomy, you ask all the right questions. Certainly, Clete said the mothership’s air temperature, even outside the hibernation room, was only about fifty degrees Fahrenheit. But how far away from a G2V star can a planet be and still have a fifty-degree surface temperature? Well, the answer depends on how much carbon dioxide, water vapor, and methane there is in the atmosphere of the Tosok home world. See, those gases trap heat. You’ve heard of the greenhouse effect? It’s caused by excess amounts of them, all of which are clear, colorless gases. They’re the wild card in planetary positions. If you’ve got enough of a greenhouse effect, you could be much farther from our sun and still have surface temperatures comparable to those on Earth — in theory, there could be an Earth-like planet out in the orbit of Jupiter as long as it had enough greenhouse gases to trap sufficient heat."

"So there’s your answer," said Dale. "The Tosoks come from a planet that orbits much farther from its star than we do from ours."

"Ah, but you’re forgetting something when you say ‘its star,’ singular. Alpha Centauri is a multiple-star system. When Centauri A and B are at their closest to each other, they’re only eleven AUs apart — just about one billion miles."

Dale frowned. "So you’re saying the light from Centauri B would make things bright, even if the Tosok world orbited a long way from Centauri A?"

"No, no. Even at its closest approach, Centauri B would only appear about one percent as bright as our sun. That’s still thousands of times brighter than our full moon — meaning nights on the Tosok home world when A has set but B is still up are probably reasonably bright, but surely no brighter than our streetlights make our streets."

"Oh."

"No, the problem isn’t Alpha Centauri B’s light — it’s its gravity. Clete all this in his show. According to celestial mechanics, planetary orbits in a double-star system are stable out to a distance of one fifth the closest approach between the two stars. Since the closest A ever gets to B is eleven AUs, then planetary orbits around A are stable out to just over two AUs — just over twice as far out as Earth is from our sun."

"But farther out than that, they’re unstable?"

Frank nodded. "And an unstable orbit could be threatening them with extinction. In which case, it’s possible that they’re not just here for a visit.

The Tosok race may be looking for a new home."

"You mean, as in invading ours?"

Frank shrugged. "It’s possible."

"God."

"Exactly," said Frank. "And think about the missing body parts: the eyes are clearly one of our most fragile components. And the throat — you heard what Professor Wills said: the design makes it easy to choke to death. And the appendix, a part that can be made to burst, causing death if not treated immediately." He paused, and looked at the old lawyer. "You know what Linda Ziegler’s got Packwood Smathers doing: looking for a way to kill a Tosok, should the jury hand down a death sentence. Perhaps the Tosoks were doing something similar: looking for a way to wipe us out, to make room for them to come here."

The video monitors in Judge Pringle’s courtroom flickered into life again with a view aboard the alien mothership. But this time the images weren’t old tapes — this time, they were a live broadcast…

Francis Antonio Nobilio floated down the dim corridor of the alien ship. It was exhilarating! He felt ten years younger. There had been a hint of nausea at first, but his body had quickly gotten used to the lack of gravity, and now he was enjoying himself thoroughly. The air had a slightly salty taste, as though he were at seaside, and there were several other faint smells. Frank had never noticed a Tosok body odor before, but over the centuries the beings had spent aboard this ship, whatever normally undetectable scent they gave off had been magnified past the threshold of discernibility.

There were lots of sounds. A low-pitched electrical hum, the occasional sloshing of water or other liquids moving through pipes, and a tick-tick-ticking that Kelkad, who was accompanying Frank, said was caused by uneven heating of the ship’s hull as its orbit moved it out of the Earth’s shadow and into direct sunlight.

Frank was carrying a video camera, on loan from Court TV. He also had a radio microphone and earpiece. Kelkad, who was wearing a headset that had been specially adapted for him, had arranged for the signals to be broadcast directly from the ship to the courthouse; the problems that had prevented Calhoun from broadcasting during his original impromptu visit had proven trivial to overcome. Doubtless over a billion people the world over were watching the live broadcast — but the only audience Frank was really interested in consisted of six women and six men in the Los Angeles County Criminal Courts Building. Judge Pringle had told Dale Rice to find a way to bring the evidence there, and Dale had done precisely that.

"Dr. Nobilio," said Dale’s voice over the radio, "can you hear me?" Frank reached a hand up to adjust his headset.

"Yes."

"All right," said Dale’s voice. "The jury is present, and we would like to now continue with the testimony. Captain Kelkad, will you please escort Dr. Nobilio into the Tosok medical facilities?"