Insigna said, ‘If it's a circular orbit, it would take Nemesis just over fifty million years to make a circuit about the Sun, or, more properly, about the center of gravity of the system, with the Sun making a similar circuit. The line between the two, as they moved, would always pass through that center. On the other hand, if Nemesis is following a highly elliptical orbit and is now at its farthest - as it must be, for if it ventured farther still, it would certainly not be a companion star - then perhaps as little as twenty-five million years.’
‘Last time, then, that Nemesis was in this position, more or less between Alpha Centauri and the Sun, Alpha Centauri must have been in a much different position than it is now. Twenty-five to fifty million years would move Alpha Centauri, wouldn't it? How much?’
‘A good fraction of a light-year.’
‘Would that mean that this is the first time Nemesis is being fought over by the two stars? Till now, would it have been circling peacefully?’
‘Not a chance, Janus. Even if you count out Alpha Centauri, there are other stars. One star may have arrived now, but there had to be another star in interfering distance at some other part of its orbit in the past. The orbit just isn't stable.’
‘What's it doing here in our neighborhood, then, if it isn't orbiting the Sun?’
‘Exactly,’ said Insigna.
‘What do you mean, “exactly”?’
‘If it were orbiting the Sun, it would be moving at a speed, relative to the Sun, of somewhere between eighty and one hundred meters a second, depending on Nemesis' mass. That's very slow motion for a star, so it would seem to stay in the same place for a long time. It would therefore remain behind the cloud for a long time, especially if the cloud is moving in the same direction relative to the Sun. With such a slow motion and its light dimmed, it's no wonder it's never been noticed till now. However-’ She paused.
Pitt, who made no effort to seem devouringly interested, sighed and said, ‘Well? Can you get to the point?’
‘Well, if it's not in orbit about the Sun, then it is in independent motion and it should be moving relative to the Sun at a hundred kilometers a second or so, a thousand times as fast as if it were in orbit. It just happens to be in our neighborhood now, but it is moving on, will pass the Sun, and will never return. But, just the same, it stays behind the cloud, scarcely budging from its position.’
‘Why should that be?’
‘There's one way it can be moving at a good clip, and yet not seem to be moving from its position in the sky.’
‘Don't tell me it's vibrating back and forth.’
Insigna's lip curled. ‘Please don't try to make jokes, Janus. This isn't funny. Nemesis might be moving more or less straight toward the Sun. It wouldn't be shifting either to the right or left, so that it would not seem to be changing position, but it would be coming right toward us; that is, right toward the Solar System.’
Pitt stared at her in surprise. ‘Is there evidence for that?’
‘Not yet. There was no reason to take the spectrum of Nemesis when it was first spotted. It was only after I had noticed the parallax that a spectral analysis would have made sense, and then I never got around to it. If you remember, you put me at the head of the Far Probe project, and told me to direct everyone's attention away from Nemesis. I couldn't have arranged a close spectral analysis at that time, and since the Leaving - well, I haven't. But I will investigate the matter now, you can be sure.’
‘Let me ask you a question. Wouldn't it produce the same effect of motionlessness, if Nemesis were moving directly away from the Sun? It's a fifty-fifty chance whether it's moving toward the Sun or away from it, isn't it?’
‘Spectral analysis will tell us. A red shift of the spectral lines will mean there's a recession; a violet shift, an approach.’
‘But it's too late now. If you take its spectrum, it will tell you it's approaching us, because we're approaching it.’
‘Right now, I wouldn't take the spectrum of Nemesis. I'd take it of the Sun. If Nemesis is approaching the Sun, then the Sun will be approaching Nemesis, and we can allow for our own motion. Besides, we're slowing and, in a month or so, we will be moving so slowly that our motion won't be affecting the spectroscopic results appreciably.’
For the space of half a minute, Pitt seemed lost in thought, staring at his uncluttered desk, his hand slowly stroking the computer terminal. Then he said, without bothering to look up, ‘No. These are observations that need not be made. I don't want you worrying yourself about it any more, Eugenia. It's a nonproblem, so just forget it.’
The wave of his hand made it clear that she was to leave.
Insigna's breath made a whistling sound as it was forced out of angrily tightened nostrils. She said in a low husky voice, ‘How dare you, Janus? How dare you?’
‘How dare I what?’ Pitt frowned.
‘How dare you order me out of here as though I were a computer-puncher? If I hadn't found Nemesis, we wouldn't be here. You wouldn't be Commissioner-elect. Nemesis is mine. I have a say in it.’
‘Nemesis isn't yours. It's Rotor's. So please leave now and let me get on with the business of the day.’
‘Janus,’ she said, raising her voice. ‘I tell you again that, in all likelihood, Nemesis is moving toward our Solar System.’
‘And I tell you again that it is only a fifty-fifty chance that it is. And even if it were heading toward the Solar System - not our Solar System any longer, by the way, but their Solar System - don't tell me it's going to hit the Sun. I won't believe you if you do. In its whole nearly five-billion-year history, the Sun has never been struck by a star, or even come close. The odds against stellar collisions even in relatively crowded parts of the Galaxy are enormous. I may not be an astronomer, but I know that much.’
‘Odds are just odds, Janus, not certainties. It's conceivable, however unlikely, that Nemesis and the Sun might collide, but I recognize that it's very unlikely they will. The trouble is that a close approach, even without collision, might be fatal to Earth.’
‘How close is a close approach?’
‘I don't know. It will take a great deal of computation.’
‘All right, then. You suggest that we take the trouble to make the necessary observations and computations and, if we find out that the situation is indeed fraught with danger to the Solar System, then what? Do we warn the Solar System?’
‘Well, yes. What choice would we have?’
‘And how would we warn them? We have no means of hypercomrnunication and, even if we had, they have no system for receiving hypermessages. If we sent out a luminal message of some sort - light, micro-waves, modulated neutrinos - it would take over two years to reach Earth, assuming we have a beam powerful enough, or sufficiently coherent. And even then, how would we know if they had received it? If they had and bothered to answer, that answer would take another two years to return. And what will be the final result of the warning? We will have to tell them where Nemesis is and they will see that the information is coming from that direction. The whole point of our secrecy, the whole plan for establishing a homogeneous civilization around Nemesis, free of interference, would be lost.’
‘Whatever the cost, Janus, how could you consider not warning them?’
‘Where's your concern? Even if Nemesis is moving toward the Sun, how long would it take for it to reach the Solar System?’
‘It could reach the neighborhood of the Sun in five thousand years.’
Pitt sat back in his chair and regarded Insigna with a kind of wry amusement. ‘Five thousand years. Only five thousand years? Look, Eugenia, two hundred and fifty years ago, the first Earthman stood on the Moon. Two and a half centuries have passed and here we are at the nearest star. Where will we be in another two and a half centuries, at this rate? At any star we wish. And in five thousand years, fifty centuries, we will be all over the Galaxy, barring the presence of other intelligent forms of life. We will be reaching out to other galaxies. Within five thousand years, technology will have advanced to the point where, if the Solar System were really in trouble, all its Settlements and its entire planetary population could take off for deep space and other stars.’