In the novel Pushing Ice, the moon Janus has a habit of killing and recycling people who repeat the same path on its surface too often. This means that the settlers need to choose random paths when they walk around. I may have missed it, but is it ever explained why Janus does this, or how the settlers realised that people were being swallowed by the moon because of the repetition of their movements?

  • 2
    Personall,y I found this to be one of the weakest points of the book. It's a clever idea but stupid once you look into it in any detail. After all how 'random' do you have to be to avoid being destroyed? Human beings (and by extension other beings) thrive on regular activity such as mealtimes, sleep cycles, workign practices, and so on.
    – user8416
    Commented Jan 2, 2013 at 8:35

2 Answers 2


This is explained at the beginning of chapter 15.

The machinery was vigilant for patterns. In particular, it was designed to recognize repetitive actions.

The next few pages explain how the settlers realized what was going on — by a combination of luck, careful observation, good intuition, and thanks to the sacrifice of two lives.

I do not recall it being explained why Janus destroys people who follow repetitive routes. One conjecture is that it considers repetitive patterns a potential threat from sentient beings, but random movement a normal part of nature. Another, contradictory conjecture is that it considers repetitive movement a natural phenomenon that can be exploited for energy, but random patterns a sign of sentient life. Either way, Janus emits warning before “eating” people, but either by design or by oversight, it only warns with Spican symbols that the Terrans cannot read.

  • A threat was expressed anyway. Hence it seems to be a kind of (brutal) intelligence test intended to get rid of stupid automatic probes, stray machines, etc. Commented May 18, 2020 at 11:47

I like the other answer but I think there was another reason as well.

At a certain point it is mentioned that the Janus moons are like a trap to collect species and give them a challenging environment to focus on survival instead of fighting each other.

I always assumed that the pattern detection was part of this. To make the environment seem threatening. In human zoo design it would be unethical to add challenges that actually injure or kill animals, but the Spicans had no such qualms (and neither do humans when experimenting on animals, thinking of it...).

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