Nemesis by Isaac Asimov Page B

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 forby 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 short-wave 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 seem 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