Planetary Engineering

Starfarers, 25.

To generate atmosphere and hydrosphere for a planet that they are "terraforming," the Tahirians use not only cometary matter but also an ice-covered outer satellite, propelling its disassembled pieces on a collision course. Next they enclose the planet inside a transparent sphere that must be opened and closed to admit spaceships. The sphere is upheld by pillars interacting like organisms with geology and wind. Tahirians and their human guests travel up and down a pillar to inspect the process. Biological/nanorobotic germs, swarming and aggregating in the surface water, gnaw rock into soil. Using self-maintaining, self-reproducing robots, the stable Tahirian civilization will complete this project in half a billion years. A sensor-computer network resembling a metal forest blinks in code, giving orders to mobile machines of wildly different shapes. There is smoke, steam, vapor and noise. Mountain-sized machines, covered in towers and trackways, artificially control plate tectonics by drilling down to the core, preventing volcanoes but bleeding core energy into surface streams of lava that can be used geochemically to stabilize air and regulate greenhouse. The artificial process will become natural and self-operating over billions of years.