Outside the valley entrance they hid their boulder cars in a knot of boulders, and Coyote studied weather reports. Maya fumed at the delay, but Coyote shrugged her off. “This isn’t going to be easy,” he told her sternly, “and it isn’t possible at all except in certain circumstances. We need to wait for some reinforcements to arrive, and we need to wait on the weather. This is something Spencer and Sax himself helped me to set up, and it is very clever, but the initial conditions have to be right.”

He returned to his screens, ignoring them all, talking to himself or to the screens, his dark thin face flickering in their light. Alchemist indeed, Michel thought, muttering as if over alembic or crucible, working his transmutations on the planet . . . a great power. And now focused on the weather. Apparently he had discovered some prevailing patterns in the jet stream, tied to certain anchoring points in the landscape. “It’s a question of the vertical scale,” he said brusquely to Maya, who with all her questions was beginning to sound like Art Randolph. “This planet has a thirty-k span top to bottom. Thirty thousand meters! So there are strong winds.”

“Like the mistral,” Michel offered.

“Yes. Katabatic winds. And one of the strongest of them drops off the Great Escarpment here.”

The prevailing winds in the region, however, were westerlies. When these hit the Echus cliff, towering updrafts resulted, and flyers living in Echus Overlook took advantage of them for sport, flying all day in gliders or birdsuits. But fairly frequently cyclonic systems came by, bringing winds from the east, and when that happened cold air ran over the snow-covered Lunae plateau, scouring snow and becoming denser and colder, until the entire drainage area was funneled out through notches in the great cliff’s edge, and the winds then fell like an avalanche.

Coyote had studied these katabatic winds for some time, and his calculations had led him to believe that when conditions were right— sharp temperature contrasts, a developed storm track east to west across the plateau— then very slight interventions in certain places would cause the downdrafts to turn into vertical typhoons, smashing down into Echus Chasma and blasting north and south with immense power. When Spencer had identified for them the nature and purpose of the new settlement in Kasei Vallis, Coyote had immediately decided to try to create the means to effect these interventions.