SPIN

Lots to eat, if ice and dust are what you eat.

Wun leaned forward in his chair. His eyes, couched in skin like crumpled leather, were bright. He smiled, which I had learned to interpret as a signal of earnestness: Martians smile when they speak from the heart.

"This was not uncontroversial for my people. What you hold in your hand has the power to substantially transform not only our own solar system but many others. And of course the outcome is uncertain. While the replicators are not organic in the conventional sense, they are alive. They're living autocatalytic feedback loops, subject to modification by environmental pressure. Just like human beings, or bacteria, or, or—"

"Or murkuds," I said.

He gri

"In other words, they might evolve."

"They will evolve, and unpredictably. But we've placed some limits on that. Or we believe we have. As I said, controversy abounds."

Whenever Wun talked about Martian politics, I envisioned wrinkly men and women in pastel togas debating abstractions from stainless steel podiums. In fact, Wun insisted, Martian parliamentarians behaved more like cash-strapped farmers bickering at a grain auction; and the clothing—well, I didn't even try to picture the clothing; on formal occasions Martians of both sexes tended to dress like the queen of hearts in a Bicycle deck.

But while the debates had been long and heartfelt, the plan itself was relatively simple. The replicators would be delivered scattershot into the far, cold extremities of the solar system. Some infinitesimally small fraction of those replicators would alight on two or three of the cometary nuclei that constitute the Oort Cloud. There they would begin to reproduce.

Their genetic information, Wun said, was encoded into molecules that were thermally unstable anywhere warmer than the moons of Neptune. But in the hypercold environment for which they had been designed, submicroscopic filaments in the replicators would begin a slow, painstaking metabolism. They grew at speeds that would make a bristle-cone pine look rushed, but grow they would, assimilating trace volatiles and organic molecules and shaping ice into cellular walls, ribs, spars, and joiners.

By the time the replicators had consumed a few hundred cubic feet of cometary nucleus, give or take, their interco

In a decade or so the replicator colony would have made of itself a sophisticated communal entity capable of recording and broadcasting rudimentary data about its environment. It would look at the sky and ask: Is there a planet-sized dark body circling the nearest star?

Posing and answering the question would consume more decades of time, and at least initially the answer was a foregone conclusion: yes, two worlds circling this star were dark bodies, Earth and Mars.

Nevertheless—patiently, doggedly, slowly—the replicators would collate this data and broadcast it back to their point of origin: to us, or at least to our listening satellites.

Then, in its senescence as a complex machine, the replicator colony would break down into individual clusters of simple cells, identify another bright or nearby star, and use accumulated volatiles mined from the host cometary nucleus to propel its seeds out of the solar system. (They would leave behind a tiny fragment of themselves to act as a radio repeater, a passive node in a growing network.)

These second-generation seeds would drift in interstellar space for years, decades, mille

Some few would reach the icy halo of a nearby star and begin the cycle anew, this time gathering fresh information, which they would eventually send home in bursts of data, brief digital orgasms. Binary star, they might say, no dark planetary bodies; or they might say, White dwarf star, one dark planetary body.

And the cycle would repeat again.

And again.

And again, one star to the next, stepwise, centuries by mille

Information passed at light-speed node-to-node would be forwarded, would modify behavior, would direct new replicators toward unexplored territory, would suppress redundant information so that core nodes were not overwhelmed. In effect we would be wiring the galaxy for a kind of rudimentary thought. The replicators would build a neural network as big as the night sky, and it would talk to us.

Were mere risks? Of course there were risks.

Absent the Spin, Wun said, the Martians would never have approved such an arrogant appropriation of the galaxy's resources. This wasn't just an act of exploration; it was an intervention, an imperial reordering of the galactic ecology. If there were other sentient species out there—and the existence of the Hypothetical had pretty much answered that question in the affirmative—the dispersal of the replicators might be misunderstood as aggression. Which might invite retaliation.

The Martians had only reconsidered this risk when they detected Spin structures under construction above their own northern and southern poles.

"The Spin renders objections moot," Wun said, "or nearly so. With luck the replicators will tell us something important about the Hypotheticals, or at least the extent of their work in the galaxy. We might be able to discern the purpose of the Spin. Failing that, the replicators will serve as a sort of warning beacon to other intelligent species facing the same problem. Close analysis would suggest to a thoughtful observer the purpose for which the network was constructed. Other civilizations might choose to tap into it. The knowledge could help them protect themselves. To succeed where we failed."

"You think we'll fail?"

Wun shrugged. "Haven't we failed already? The sun is very old now. You know that, Tyler. Nothing lasts indefinitely. And under the circumstances, for us, even 'indefinitely' isn't a very long time."

Maybe it was the way he said it, smiling his sad little Martian sincerity-smile and leaning forward in his wicker chair, hit the weight of the pronouncement was quietly shocking.

Not that it surprised me. We all knew we were doomed. Doomed, at the very least, to live out our lives under a shell that was the only thing protecting us from a hostile solar system. The sunlight that had made Mars habitable would cook the Earth if the Spin membrane was stripped away. And even Mars (in its own dark envelope) was rapidly slipping out of the so-called habitable zone. The mortal star that was the mother of all life had passed into bloody senescence and would kill us without conscience.

Life had been born on the fringe of an unstable nuclear reaction. That was true and it had always been true; it had been true before the Spin, even when the sky was clear and summer nights twinkled with distant, irrelevant stars. It had been true but it hadn't mattered because human life was short; countless generations would live and die in the span of a solar heartbeat. But now, God help us, we were outliving the sun. Either we would end up as cinders circling its corpse or we would be preserved into eternal night, encapsulated novelties with no real home in the universe.