Permanence

Prologue

THE DISCOVERY THAT made interstellar travel possible and an interstellar civilization inevitable, was made in 1997; but at the time no one recognized its significance.

Maria Teresa Ruiz, an astronomer at the Universidad de Chile, was searching for white dwarf stars when she spotted something unusual. Thirty light-years away, in the constellation Hydra, a very faint red pinprick of light lay adrift. Its spectrum didn't show titanium oxide, which would have marked it as a red dwarf star. Instead, Ruiz found the unmistakable signature of lithium in its atmosphere— an impossibility for any real star. She named the object Kelu-1, the first free-floating brown dwarf ever seen.

The first brown dwarfs, Gliese 229B and Teide 1, had been spotted two years before, within weeks of one another. Too small to be stars, but too large to be planets, such galactic oddities glowed faint red from the heat of their slow gravitational contraction. Young dwarfs were hot enough to sustain Earthlike conditions on planets that might orbit them. The first dwarfs spotted had orbited around known stars, but Ruiz's find was different. Kelu-1 floated free of any stellar influence. It was a place in its own right, an invisible sun between suns.

Astronomers had theorized the existence of such interstellar solitaries; what they hadn't imagined was just how common they were. True, some astronomers had an inkling: in 1984 Bahcall declared that "about half of the [galactic] disk material at the solar position has not yet been observed." Some of this material would be stars whose distance had not yet been determined correctly— tiny red dwarfs, for the most part, which were close but looked remote. Still, he estimated that about a hundredth of a solar mass per cubic parsec was unaccounted for— was not, in fact, embodied in the Lit Stars.

Within a year of Ruiz's discovery astronomers were finding brown dwarfs all over the place, prompting J. Davy Kirkpatrick to declare in 1998 that they were "the most common spectral type in the galaxy." In a press release he went on to add that "They are so commonplace that there is a good chance that we will discover one which lies closer to the sun than Proxima Centauri, the closest of the known stars."

He was right: Nemesis was discovered several years later. But even those astronomers who had come to suspect that the galaxy held more brown dwarfs than lit stars still failed to grasp the implications. Like everyone else on Earth at this time, when they thought about the future expansion of humanity into space, they pictured colonies on single, Earthlike worlds orbiting Sunlike stars. And since there were only six G-class stars within twenty light-years, their dreams were spare and even forlorn— of six tiny settlements huddling on worlds separated by generations of travel time. Such settlements would only be reached using colossal, expendable starships capable of carrying a mere handful of people at some small fraction of light speed.

But the brown dwarfs each had their retinue of planets— the halo worlds, as they came to be called. And though they were not lit to the human eye, many of these planets were bathed in hot infrared radiation. Many were stretched and heated by tidal effects, like Io, a moon of Jupiter and the hottest place in the Solar System. And while Jupiter's magnetic field was already strong enough to heat its moons through electrical induction, the magnetic field of a brown dwarf fifty times Jupiter's mass radiated unimaginable power— power enough to heat worlds. Power enough to sustain a population of billions; enough to launch starships.

Did Dr. Ruiz ever step outside and gaze up at the stars and think that for every star she saw, there were five she could not see? Did she realize that the moment she discovered Kelu-1, she had taken star travel from dream to possibility? For although the stars were as far away as ever, with her discovery the known distance between planetary systems had been halved.