Nebula Awards Showcase 2012 by John Kessel, James Patrick Kelly

I can’t terraform Venus,” he said. “So tell me more about Mars.”
     
    I could see that there was something that he was keeping back. Carlos Fernando had some idea that he wasn’t telling.
     
    But Leah did not press him, and instead took the invitation to tell him about her studies of the ecology on Mars, as it had been transformed long ago by the vanished engineers of the long-gone Freehold Toynbee colony. The Toynbee’s engineers had designed life to thicken the atmosphere of Mars, to increase the greenhouse effect, to melt the frozen oceans of Mars.
     
    “But it’s not working,” Leah concluded. “The anaerobic life is being out-competed by the photosynthetic oxygen-producers. It’s pulling too much carbon dioxide out of the atmosphere.”
     
    “But what about the Gaia effect? Doesn’t it compensate?”
     
    “No,” Leah said. “I found no trace of a Lovelock self-aware planet. Either that’s a myth, or else the ecology on Mars is just too young to stabilize.”
     
    “Of course on Venus, we would have no problem with photosynthesis removing carbon dioxide.”
     
    “I thought you weren’t interested in terraforming Venus,” I said.
     
    Carlos Fernando waved my objection away. “A hypothetical case, of course,” he said. “A thought exercise.” He turned to Leah. “Tomorrow,” he said, “would you like to go kayaking?”
     
    “Sure,” she said.
     
    ~ * ~
     
    Kayaking, on Venus, did not involve water.
     
    Carlos Fernando instructed Leah, and Epiphany helped me.
     
    The “kayak” was a ten-meter long gas envelope, a transparent cylinder of plastic curved into an ogive at both ends, with a tiny bubble at the bottom where the kayaker sat. One end of the kayak held a huge, gossamer-bladed propeller that turned lazily as the kayaker pedaled, while the kayaker rowed with flimsy wings, transparent and iridescent like the wings of a dragonfly.
     
    The wings, I discovered, had complicated linkages; each one could be pulled, twisted, and lifted, allowing each wing to separately beat, rotate, and camber.
     
    “Keep up a steady motion with the propeller,” Epiphany told me. “You’ll lose all your maneuverability if you let yourself float to a stop. You can scull with the wings to put on a burst of speed if you need to. Once you’re comfortable, use the wings to rise up or swoop down, and to maneuver. You’ll have fun.”
     
    We were in a launching bay, a balcony protruding from the side of the city. Four of the human-powered dirigibles that they called kayaks were docked against the blister, the bulge of the cockpits neatly inserted into docking rings so that the pilots could enter the dirigible without exposure to the outside atmosphere. Looking out across the cloudscape, I could see dozens of kayaks dancing around the city like transparent squid with stubby wings, playing tag with each other and racing across the sky. So small and transparent compared to the magnificent clouds, they had been invisible until I’d known how to look.
     
    “What about altitude?” I asked.
     
    “You’re about neutrally buoyant,” she said. “As long as you have airspeed, you can use the wings to make fine adjustments up or down.”
     
    “What happens if I get too low?”
     
    “You can’t get too low. The envelope has a reservoir of methanol; as you get lower, the temperature rises and your reservoir releases vapor, so the envelope inflates. If you gain too much altitude, vapor condenses out. So you’ll find you’re regulated to stay pretty close to the altitude you’re set for, which right now is,” she checked a meter, “fifty-two kilometers above local ground level. We’re blowing west at a hundred meters per second, so local ground level will change as the terrain below varies; check your meters for altimetry.”
     
    Looking downward, nothing was visible at all, only clouds, and below the clouds, an infinity of haze. It felt odd to think of the surface, over fifty kilometers