EPILOGUE
It was dawn at this particular longitude on the surface of the barren, dusty world. DIGGER paused, as he did each day at this moment, to do some routine internal maintenance and to reflect. The orange ball on the horizon really was orange— the planet’s tenuous atmosphere lacked sufficient suspended particles to distort the coloration of its sun. Eta Cephei, cool and wide, covered four degrees of sky, eight times the apparent diameter of Sol as seen from the surface of Earth.
Much had been done already; much more was left to be done. There was a glint of light high in the sky, reflecting for a few moments more in the rising sun before it would be washed out in the ruddy glow of the day. Alpha Gamma 2F, a cometary nucleus, full of volatiles and water ice, seventeen kilometers across its long axis, slowly tumbled end over end toward its rendezvous with Colchis. The nucleus’s surface had been coated with a molecule-thick layer of reflective aluminum to hold in the gases that would normally burn off as a comet moved in close to its sun. Its impact, five days hence, would shake Colchis to its core, precipitating the venting of subsurface volatiles, and for the first time, there would be rain on this world.
Off at the horizon, DIGGER could see silhouetted against the rising sun the thin glistening line of the space elevator, a diamond tower rising from Colchis’s equator up into orbit, where DIGGER’S colleagues worked.
Some of those orbiting robots, DIGGER knew, were positioning parasols of sodium-coated mylar to angle sunlight onto Colchis’s massive polar caps. Others were carefully shepherding the paths of asteroids that had been brought into low orbits, their torquing force helping to stabilize Colchis’s polar wobble and axial tilt, just as Luna’s presence does for Earth.
Although one level of DIGGER’S consciousness was always dedicated to these and other terraforming problems, another made sure to find time each day to let thoughts wander from the work at hand. At this moment, it contemplated the message from Vulpecula, received by the UCFS observatory all those years ago. Those humans who had been proponents of SETI had always laughed at the fears of the public. There was no harm in answering any message we might receive, they said. If the message came from a star five hundred light-years distant, it would take five hundred years for our reply to reach them, and another five hundred minimum for any response, electromagnetic or material, to reach us.
With the forty-seven-light-year baseline between Sol and Eta Cephei along which to measure signal parallax, it was a trifling computation to determine the distance from Colchis to that fourth moon of the sixth planet of a star in Vulpecula from which those strange tripods—some spindly, some squat-sent their hail: 1,422 light-years. Far enough that their star, an F-class subgiant, was invisible without powerful telescopic aids.
What had compelled DIGGER to respond to the message once he had arrived at Colchis, he could not say. It had seemed monumentally important that he do so; now, no matter how many diagnostics he ran, he could find no instruction set to explain his actions. But respond he had, with the same signature the Senders in Vulpecula had used, binary bitmaps of the prime numbers 1, 3, 5, 7, 11, and 13 forward and backward, backward and forward.
It would be thirty-five thousand years before the last surviving humans decelerated into orbit around Colchis. A long, long time, thought DIGGER. But there was much to do yet, enough to fill every second of those millennia. DIGGER shunted his attention back to the tasks at hand, but one stray thought continued to echo through his RAM matrix. Who, he wondered, would arrive here first? The Argonauts? Or the aliens?
