And there was Erythro, the planet that Rotor orbited in such a way that huge Megas and ruddy Nemesis rose and set in an intricate pattern. Erythro! That had been a question from the beginning.
Pitt remembered well the early days of their entry into the Nemesis System. The limited intricacy of the planetary family of Nemesis had exposed itself little by little, as Rotor raced toward the red dwarf star.
Megas had been discovered at a distance of four million kilometers from Nemesis, only one-fifteenth the distance of Mercury from the Sun of the Solar System. Megas obtained about the same amount of energy as Earth got from its Sun, but with a lesser intensity of visible light and a higher intensity of infrared.
Megas, however, was clearly not habitable, even at first glance. It was a gas giant, with one side always facing Nemesis. Both its rotation and revolution were twenty days long. The perpetual night on half of Megas cooled it only moderately, since its own interior heat rose to the surface. The perpetual day on the other half was unendurably hot. That Megas kept its atmosphere under this heat was entirely because, with its mass higher and its radius smaller than that of Jupiter, its surface gravity was fifteen times that of Jupiter, and forty times that of Earth.
Nor did Nemesis have any other sizable planet.
But then, as Rotor drew closer, and Megas could be seen more clearly, the situation was altered again.
It was Eugenia Insigna who brought Pitt the news. It was not that she had made the discovery herself. It had merely showed up on the computer-enhanced photographs, and had been brought to Insigna's attention since she was Chief Astronomer. With considerable excitement, she had brought it to Pitt in his Commissioner's chambers.
She had begun simply enough, keeping her voice level, though it was shaking with emotion.
‘Megas has a satellite,’ she said.
Pitt had lifted his eyebrows ever so slightly, but then he said, ‘Isn't that to be expected? The gas giants of the Solar System have anywhere up to a score of satellites.’,
‘Of course, Janus, but this is not an ordinary satellite. It's large.’
Pitt kept his cool. ‘Jupiter has four large satellites.’
‘I mean, really large, with almost Earth's size and mass.’
‘I see. Interesting.’
‘More than that. Much more than that, Janus. If this satellite revolved about Nemesis directly, tidal influences would cause only one side to face Nemesis, and it would be uninhabitable. Instead, only one side faces Megas, which is much cooler than Nemesis. Furthermore, the satellite's orbit is tilted substantially to Megas' equator. This means that in the satellite's sky, Megas is seen from only one hemisphere and it moves north and south with a cycle of about one day, while Nemesis moves across the sky, rising and setting, again with a cycle of one day. One hemisphere has twelve hours of darkness and twelve hours of light. The other hemisphere has the same but during its daytime, Nemesis is frequently in eclipse for up to half an hour at a time, with the cooling made up for by Megas' mild warmth. During the dark hours, in that hemisphere, the darkness is ameliorated by Megas' reflected light.’
‘The satellite has an interesting sky, then. How fascinating for astronomers.’
‘It's not just an astronomical lollipop, Janus. It's possible that the satellite has an equable temperature at the right range for human beings. It may be a habitable world.’
Pitt smiled. ‘Even more interesting, but it wouldn't have our kind of light, though, would it?’
Insigna nodded. ‘That's true enough. It would have a ruddy sun and a dark sky because there would be no shortwave light to be scattered. And there would be a reddish landscape, I suppose.’
‘In that case, since you named Nemesis, and one of your people named Megas, I'll take the privilege of naming the satellite. Call it Erythro, which if I recall correctly, is related to the Greek word for “red.” ’
The news remained good for quite some time thereafter. An asteroid belt of respectable size was located beyond the orbit of the Megas-Erythro system, and those asteroids would clearly be an ideal source of material for building more Settlements.
And as they approached Erythro, the nature of its habitability seemed to grow ever more favorable. Erythro was a planet of sea and land, though its seas, from preliminary estimates of its cloud cover as made out in visible light and the infrared, seemed shallower than Earth's oceans, and really impressive mountains on the land were very few. Insigna, on the basis of further calculations, insisted that the climate on the planet as a whole would be entirely suitable for human life.
And then when the inflight had brought them to a distance from which Erythro's atmosphere could be studied spectroscopically with precision, Insigna said to him, ‘Erythro's atmosphere is a little denser than Earth's and it contains free oxygen - 16 per cent of it, plus 5 per cent argon and the rest nitrogen. There must be small quantities of carbon dioxide, but we haven't detected it yet. The point is, it's a breathable atmosphere.’
‘Sounds better and better,’ said Pitt. ‘Who could have imagined this when you first spotted Nemesis?’
‘Better and better for the biologist. Maybe not very good for Rotor on the whole, though. A sizable content of free oxygen in the atmosphere is a sure indication of the presence of life.’
‘Life?’ said Pitt, momentarily stupefied at the thought.
‘Life,’ said Insigna, boring in, taking an apparent perverse pleasure in stressing the possibilities. ‘And if life, then possibly intelligent life, perhaps even a high civilization.’
17What followed was a nightmare for Pitt. He had not only to live with the terrible apprehension of his own Earth-people pursuing and overtaking him, superior in number certainly, and in technology possibly - but there was an accompanying fear now that was, if anything, greater. They might be approaching and infringing on an old and advanced civilization capable of eradicating them in a moment of absent-minded annoyance as a human being might, without thinking, crush a mosquito that buzzed too near his ear.
As they continued to approach Nemesis, Pitt said to Insigna with a deeply troubled air, ‘Need oxygen truly imply the existence of life?’
‘It's a thermodynamic inevitability, Janus. In an Earth-like planet - and, as nearly as we can tell, Erythro is Earth-like - free oxygen cannot exist, any more than in any Earth-like gravitational field, a rock can be suspended in open air of its own accord. Oxygen, if present in the atmosphere to begin with, would spontaneously combine with other elements in the soil, giving off energy. It would only continue to exist in the atmosphere if some process were to supply energy and continually regenerate free oxygen.’
‘I understand that, Eugenia, but why need the energy-supply process necessarily involve life?’
‘Because nothing has ever been encountered in nature that would do the job, except the photosynthetic action of green plants that make use of solar energy to release oxygen.’
‘When you say “nothing has ever been encountered in nature,” you mean in the Solar System. This is another system with a different sun and a different planet under different conditions. The laws of thermodynamics may still hold, but what if there is some chemical process that we haven't encountered in the Solar System and that is forming the oxygen here?’
‘If you're a betting man,’ said Insigna, ‘don't bet on it.’
What was needed was evidence, and Pitt had to wait for the evidence to appear.
To begin with, Nemesis and Megas turned out to have extremely weak magnetic fields. This created no particular stir for it had been expected, since both star and planet rotated very slowly. Erythro, with a rotational period of twenty-three hours and sixteen minutes (equal to the period of its revolution about Megas), had a magnetic field that was similar, in intensity, to Earth's.
Insigna expressed her satisfaction. ‘At least we don't have to worry about dangerous radiation effects from intense magnetic fields, especially since Nemesis' stellar wind is bound to be much less intense than that of the Sun. That's good, because it means we might be able to detect the presence or absence of life on Erythro at a distance. Technological life, anyway.’