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BDO of the Day: Janus

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Today’s Big Dumb Object (BDO) is Janus, the moon of Saturn, which in Alastair Reynolds' Pushing Ice turns out to be much more than it seems.

It turns out that Janus’s weird co-orbit with Epimetheus wasn’t an accident but an alien plot to disguise a BDO as a moon until humanity became interesting enough to chase a suddenly de-iced and de-orbiting Janus out of the solar system as it makes its surprise trip to Virgo. The anti-heroes of the story don’t actually intend to pursue Janus that far; they were out mining ice from a comet when Janus took flight, and they happened to be the only ship close enough to its flight path to investigate.


Due to forces beyond their immediate understanding, the humans end up stuck on Janus for the long haul. They build a small colony on some of the remaining ice cover of Janus, and draw power from the mysterious machinery that seems to form the vast majority of the erstwhile moon. No numbers are given for the thickness of ice lost, but the general impression one gets from the story is that Janus is about as big as it ever was, which is to say, about 200 kilometers (125 miles) in its longest dimension, and 716,000 cubic kilometers, or 172,000 cubic miles, in volume.

The humans barely survive the ordeal, and never gain much understanding of the mechanical workings of Janus or of its language of colorful lights. Nor do they find any aliens within; Janus seems to be fully automated and nothing more than a trap intended to transport them to Virgo. They know from observations made back in their own solar system that another megastructure awaits them there. A pipe-shaped skeletal structure “seventeen or eighteen light-seconds wide, and nearly 3 light minutes long” hovers at the Lagrange point between the two stars of the binary star system of Alpha Virginis, a.k.a., Spica. (That’s 3 and a quarter million miles in diameter by 33 million miles long.)

However, as they near Spica after twelve years, Janus sprouts a shell and the view of the megastructure is hidden from them for another year or so. Eventually, however, aliens cut a hole through the shell, and the humans see the empty megastructural tube they’ve been expecting. There are doors at the ends of the tube, but they’re closed.

They make first contact with the alien drillers, who are cagey about their technology and knowledge, but do provide resurrection and rejuvenation services freely. This allows the story’s timeline to drag on for several more decades than one might have expected or wanted. On the bright side, a resurrection leads to social change in the odd culture that has developed on Janus; the rather psychopathic character who was in charge for most of the story to date is replaced by the anointed heroine of the story, Bella Lind.

(Bella was anointed in a rather disappointing frame story in which far future humans discuss her vital importance to all humanity, so I spent the whole story waiting for her amazing contribution to mankind to happen. It turns out to be some silly CNN interviews she did on the way to investigate Janus that somehow inspired…something, I’m not sure what. In return for this great gift, the future humans send out a package of magical nanotechnology to help her, and she wastes it all undoing a mess made by the psychopath in one neighborhood on Janus, even though the psychopath has already managed to doom all of Janus by that point in the story by betraying humanity to some hostile aliens. The magical nanotech also tells Bella that they’re not at Spica anymore, that Janus only picked up more relativistic speed there and sped away far, far into the future, which is how someone from Bella’s far future could contact a famous character of the past like Bella.)

The psychopath redeems herself—not through any convincing repentance of her destructive behavior, but by going out the hole Janus has blown in the tube and sending back pictures of this third megastructure. And boy, is it mega. The tube the humans used to inhabit before the perverse destruction of Janus, is just one glowing twig in a braided rope that itself is only a small part of a “torus of light” the size of an entire solar system. Things are not going well here at the end of time, however; the center of the torus is missing like the megastructure’s creators, and the ropes leading to it are as frayed as the relations between the various alien species within the structure.

There are some impressive BDOs in this story, but the apparent failure of the megastructure builders to survive their project of creating a congress or zoo at the end of the universe, and the many actual failures of the humans to behave decently, never mind heroically, make this story more depressing than your average abandoned BDO story. The flip side of the sense of wonder is a sense of horror.