They'd looked forward to many more.

Now, though, all she could think of was the fact that such crystal fields occurred in regions associated with sulfur geysers, lateral plumes, and volcanic hot spots.

Something funny was happening to the far edge of the field, though. She cranked up her helmet to extreme magnification and watched as the trail slowly erased itself. New flowers were rising up in place of those she had smashed, small but perfect and whole. And growing. She could not imagine by what process this could be happening. Electrodeposition? Molecular sulfur being drawn up from the soil in some kind of pseudocapillary action? Were the flowers somehow plucking sulfur ions from Io's almost nonexistent atmosphere?

Yesterday, the questions would have excited her. Now, her capacity for wonder was nonexistent. Moreover, her instruments were back in the moonrover. Save for the suit's limited electronics, she had nothing to take measurements with. She had only herself, the sledge, the spare airpacks, and the corpse.

"Damn, damn, damn," she muttered. On the one hand, this was a dangerous place to stay in. On the other, she'd been awake almost twenty hours now and she was dead on her feet. Exhausted. So very, very tired.

"O sleep! It is a gentle thing. Beloved from pole to pole. Coleridge."

Which, God knows, was tempting. But the numbers were clear: no sleep. With several deft chin-taps, Martha overrode her suit's safeties and accessed its medical kit. At her command, it sent a hit of methamphetamine rushing down the drug/vitamin catheter.

There was a sudden explosion of clarity in her skull and her heart began pounding like a jackhammer. Yeah. That did it. She was full of energy now. Deep breath.

Long stride. Let's go.

No rest for the wicked. She had things to do. She left the flowers rapidly behind.

Good-bye, Oz.

Fade out. Fade in. Hours had glided by. She was walking through a shadowy sculpture garden. Volcanic pillars (these were their second great discovery; they had no exact parallel on Earth) were scattered across the pyroclastic plain like so many isolated Lipschitz statues. They were all rounded and heaped, very much in the style of rapidly cooled magma. Martha remembered that Burton was dead, and cried quietly to herself for a few minutes.

Weeping, she passed through the eerie stone forms. The speed made them shift and move in her vision. As if they were dancing. They looked like women to her, tragic figures out of The Bacchae or, no, wait, The Trojan Women was the play she was thinking of. Desolate. Filled with anguish. Lonely as Lot's wife.

There was a light scattering of sulfur dioxide snow on the ground here. It sublimed at the touch of her boots, turning to white mist and scattering wildly, the steam disappearing with each stride and then being renewed with the next footfall. Which only made the experience all that much creepier.

Click.

"Io has a metallic core predominantly of iron and iron sulfide, overlain by a mantle of partially molten rock and crust."

"Are you still here?"

"Am trying. To communicate."

"Shut up."

She topped the ridge. The plains ahead were smooth and undulating. They reminded her of the Moon, in the transitional region between Mare Serenitatis and the foothills of the Caucasus Mountains, where she had undergone her surface training. Only without the impact craters. No impact craters on Io. Least cratered solid body in the solar system. All that volcanic activity deposited a new surface one meter thick every millennium or so. The whole damned moon was being constantly repaved.

Her mind was rambling. She checked her gauges, and muttered, "Let's get this show on the road."

There was no reply.

Dawn would come–when? Let's work this out. Io's "year," the time it took to revolve about Jupiter, was roughly forty-two hours fifteen minutes. She'd been walking seven hours. During which Io would've moved roughly sixty degrees through its orbit. So it would be dawn soon. That would make Daedalus's plume less obvious, but with her helmet graphics that wouldn't be a worry. Martha swiveled her neck, making sure that Daedalus and Jupiter were where they ought to be, and kept on walking.

Trudge, trudge, trudge. Try not to throw the map up on the visor every five minutes. Hold off as long as you can, just one more hour, okay, that's good, and another two miles. Not too shabby.

The sun was getting high. It would be noon in another hour and a half. Which meant–well, it really didn't mean much of anything.

Rock up ahead. Probably a silicate. It was a solitary six meters high brought here by who knew what forces and waiting who knew how many thousands of years just for her to come along and need a place to rest. She found a flat spot where she could lean against it, and, breathing heavily, sat down to rest. And think. And check the airpack. Four hours until she had to change it again. Bringing her down to two airpacks. She had slightly under twenty-four hours now. Thirty-five miles to go. That was less than two miles an hour. A snap. Might run a little tight on oxygen there toward the end, though. She'd have to take care she didn't fall asleep.

Oh, how her body ached.

It ached almost as much as it had in the '48 Olympics, when she'd taken the bronze in the women's marathon. Or that time in the internationals in Kenya when she'd come up from behind to tie for second. Story of her life. Always in third place, fighting for second. Always flight crew and sometimes, maybe, landing crew, but never the commander. Never class president. Never king of the hill. Just once–once!–she wanted to be Neil Armstrong.

Click.

"The marble index of a mind forever. Voyaging through strange seas of thought, alone. Wordsworth."

"What?"

"Jupiter's magnetosphere is the largest thing in the solar system. If the human eye could see it, it would appear two and a half times wider in the sky than the sun does."

"I knew that," she said, irrationally annoyed.

"Quotation is. Easy. Speech is. Not."

"Don't speak, then."

"Trying. To communicate!"

She shrugged. "So go ahead–communicate."

Silence. Then, "What does. This. Sound like?"

"What does what sound like?"

"Io is a sulfur-rich, iron-cored moon in a circular orbit around Jupiter. What does this. Sound like? Tidal forces from Jupiter and Ganymede pull and squeeze Io sufficiently to melt Tartarus, its sub-surface sulfur ocean. Tartarus vents its excess energy with sulfur and sulfur dioxide volcanoes. What does. This sound like? Io's metallic core generates a magnetic field that punches a hole in Jupiter's magnetosphere, and also creates a high-energy ion flux tube connecting its own poles with the north and south poles of Jupiter. What. Does this sound like? Io sweeps up and absorbs all the electrons in the million-volt range. Its volcanoes pump out sulfur dioxide; its magnetic field breaks down a percentage of that into sulfur and oxygen ions; and these ions are pumped into the hole punched in the magnetosphere, creating a rotating field commonly called the Io torus. What does this sound like? Torus. Flux tube. Magnetosphere. Volcanoes. Sulfur ions. Molten ocean. Tidal heating. Circular orbit. What does this sound like?"

Against her will, Martha had found herself first listening, then intrigued, and finally involved. It was like a riddle or a word-puzzle. There was a right answer to the question. Burton or Hols would have gotten it immediately. Martha had to think it through.

There was the faint hum of the radio's carrier beam. A patient, waiting noise.

At last, she cautiously said, "It sounds like a machine."

"Yes. Yes. Yes. Machine. Yes. Am machine. Am machine. Am machine. Yes.

Yes. Machine. Yes."

"Wait. You're saying that Io is a machine? That you're a machine? That you're Io?"