On Venus there was the thick, soupy atmosphere and the verdant tropical jungles. On Mars, the rusty desert and the ruins of an eon-old civilization. But on Mercury you knew at once that you trod upon an alien world. At perihelion, the sun swelled to almost four times its size as seen from Earth, and because Mercury's tenuous atmosphere had boiled off into space half a billion years ago, the sky was black. The sun had lost its spherical shape, too. Great solar prominences licked out at the blackness, and the visible corona seemed to swell and pulse.
Underfoot, Steve could feel the crunchy ground powdering beneath his asbestos boots with every step. And far off toward the horizon, a jagged ridge of blood-red mountains bit at the black sky like festering, toothless gums.
Before long, Teejay's voice sang in Steve's earphones. "Over here, you boys." And Steve could see her crouching, shapeless in the loose asbestos suit, off to his left. The sun's heat had parched a long, snaking crack in the surface and Steve lumbered over to it clumsily, letting his shadow fall across the crevice. "Those stone worms are umbra-tropic," he called, and waited.
"I don't wonder," said Teejay, looking up at the sun through the smoked goggles of her helmet.
The stone worms, Steve knew, were attracted by darkness—hence they generally dwelled in the deepest crevices, although a man's shadow might bring them to the surface. He'd never seen a stone worm, but he'd read about them and seen their pictures.
"You'll see something very unlovely," Teejay predicated. "The stone worm isn't a carbon-basic animal, but a silicate creature with a sodium-silicon-nitrogen economy. It's about four feet long and kind of like some ghastly white slug. It—hey, Stedman, get on your toes!"
The worm was coming.
It poked its head up out of the crevice first, and then the slug-like body followed, curling quite instinctively until the whole thing lay in Steve's shadow. Four feet long and a foot across at the middle, it looked like the product of nightmare. The head was one huge, lidless, glassy eye—with a purple-lipped mouth where the pupil should have been! The mouth opened and shut like that of a fish, but when Steve lifted the monster by its middle and brought it out into the sun, the lips puckered completely shut and the white slug began to thrash dangerously.
But under the influence of the sun's heat it soon subsided. Trouble was, Steve thought vaguely as they made their way back toward Furnacetown with the quiescent monster, the sun's heat did not subside. Probably, it was his imagination, but the sun had seemed to become, if anything, stronger. He looked at the others, but they merely walked forward, completely unconcerned. Maybe he'd tired himself subduing the stone worm, for he knew that might seem to intensify the heat.
Inside his asbestos suit, Steve began to sweat. It did not start slowly, but all at once the perspiration streamed down his face and body.