Using the figures on the present situation, Massy reluctantly arrived at the fact that here, on this already-frozen world, the temperature would drop until CO2, froze out of the atmosphere. When that happened, the temperature would plummet until there was no really significant difference between it and that of empty space. It is carbon dioxide which is responsible for the greenhouse effect, by which a planet is in thermal equilibrium only at a temperature above its surroundings—as a greenhouse in sunlight is warmer than the outside air.
The greenhouse effect would vanish soon on the colony-world. When it vanished on the mother planet—
Massy found himself thinking, If Riki won't leave when the Survey ship comes, I'll resign from the Service. I'll have to if I'm to stay. And I won't go unless she does.
III
"If you want to come, it's all right," said Massy ungraciously.
He waited while Riki slipped into the bulky cold-garments that were needed out-of-doors in the daytime, and were doubly necessary at night. There were heavy boots with inches-thick insulating soles, made in one piece with the many-layered trousers. There was the air-puffed, insulated over-tunic with its hood and mittens which were a part of the sleeves.
"Nobody goes outside at night," she said when they stood together in the cold-lock.
"I do," he told her. "I want to find out something."
The outer door opened and he stepped out. He held his arm for her, because the steps and walkway were no longer heated. Now they were covered with a filmy layer of something which was not frost, but a faint, faint bloom of powder. It was the equivalent of dust, but it was microscopic snow-crystals frozen out of the air by the unbearable chill of night.