The Diamond Moon (13 page)

, McNeil displayed the results of his measurements and cal-culations on the graphics plate. Indeed, the structures had just the right geometry to function as antennas under a moderate layer of ice.

The team was supposed to use the night hours to sleep, but the day’s events left few of them calm enough. After dinner in the wardroom, Blake left the others arguing about how and with whom the antennas communicated and went back to the ship’s cramped but well-equipped laboratory.

Having finally resorted to a laser probe and an ion trap to get a few sample molecules from the alien structure, he spent the early evening hours trying to find out what the stuff was. Spectrometry didn’t help him much: no exotic elements showed up in the peaks and valleys of the spec-trum—a few common metals, plus carbon and oxygen and nitrogen and other light elements—and not even any unu-sual ratios among them. Whatever had given the structure its extraordinary strength and durability was surely due to its crystalline structure—but that had been reduced to mo-lecular chaos when Blake blasted it with his laser.

He gave up and turned to the ice cores they had col-lected. These were more . . . suggestive.

 

He was peering at the readouts, shaking his head glumly, when he became aware that Forster was watching him from the hatch of the cramped, padded laboratory.

 

“Hello,” Blake said, “have you come to watch me learn basic college chemistry?”

 

“What are you doing?” Forster asked, eyebrows vibrat-ing.

 

“Well, sir, I could give you a list of failed experiments. Structure and composition of the ice. Age of the ice—trying to do age determinations on these core samples we took today and not succeeding.”

The surface of Amalthea, subliming into space, was con-stantly exposing fresh layers of material. The long-buried ice had been affected by particles in Jupiter’s radiation belt and by solar and cosmic rays. By measuring isotope ratios in the fresh ice, it was theoretically possible to calculate how long each layer had rested undisturbed.

“What’s the problem?”

 

“The readings are crazy. Neighboring samples give val-ues that differ by five or six orders of magnitude.”

 

“You’ve calibrated the instruments?”

 

“Yes sir. Maybe I’m misreading the manuals—maybe they were translated from Eskimo or Finno-Ugrik or something.”

 

“Why not believe the instruments? One sample’s old, another’s young.”

Blake said, “We’re not talking old and young here, sir, we’re talking young and
very
young. Most of the samples date this ice to a billion years BP. Compare that to ice from Ganymede or Callisto or Europa, which is a respectable four-point-five billion years BP.”

Forster sounded gruff, but there was a smile in his voice. “Meaning Amalthea didn’t form as part of the Jupiter sys-tem. Perhaps it was captured later.”

 

“Meaning Amalthea didn’t form as part of the solar sys-tem.” Blake grunted. “
Listen
to me, I sound like Sir Randolph-Loudmouth-Mays.”

 

“And the other sample?” Forster demanded.

 

“Somewhere between a thousand and ten thousand years old.”

 

“Not
quite
as old as the solar system,” Forster said, smil-ing openly now.

 

“Well sir, if you were a Creationist . . .”

 

“Where did that sample come from?”

 

“Right under the alien antenna,” Blake said.

 

“Might be an interesting place to start looking.” Forster sighed softly. “Too bad Troy’s not with us. Could be, that cult of hers would have something to say about these mat-ters.”

 

“She wouldn’t like to hear you call the Free Spirit her cult, Professor.”

 

“Salamander, then, or whatever you call yourselves. Pro-fessor Nagy attempted to enlighten me, but I’m afraid I was never able to get it all straight.”

 

“Besides, the Knowledge is hardly complete. It doesn’t make any reference to Amalthea,” said Blake, evading the topic.

 

“Rather odd, then, that Troy always seems to know more than this so-called Knowledge. Too bad she never stays in one place long enough to make herself useful.”

 

Blake felt his ears glowing. “She usually manages to ar-rive when she’s needed,” he said defensively. Forster of all people knew that better than most.

 

“Quite. What is she about, back there on Ganymede? Did she drop any hints in your hearing?”

 

“Sorry. I don’t know any more about it than you.”

“Hm, well . . . I wish she’d let us know earlier. Saved ourselves a week or two in that gloomy cavern.” Forster turned his attention to the lab bench, tapping the laser spectrom-eter’s little flatscreen. “What else have you got to show, my boy?”

“Take a look at the basic composition of this stuff. Look at these ratios.” Blake first showed Forster close-ups of ice crystals on the big screen, then a chemical analysis of the foreign minerals trapped in the crystals.

Looking at the colored graphics and spiky charts on the flatplate, J. Q. R. Forster’s face broadened into a truly happy grin. “Golly, Mr. Wizard.”

 

“What are you onto, sir?” Blake demanded, for it was obvious the older man was not surprised.

 

“You first, young man—what does it all mean to you?”

 

“Well, the crystalline structure’s common enough. Ordi-nary Ice I, so we know it froze at low pressure.”

 

“Surely that’s what you’d expect.”

 

“Yeah, unless Amalthea was a leftover chunk of the core of a much larger ice moon.”

 

“You considered that, did you?” Forster said apprecia-tively.

 

“It crossed my mind. See, I don’t think this stuff froze in vacuum. How could you explain these dissolved minerals—salts, carbonates, phosphates, others. . . .” He pointed to the graphic on the plate.

 

“What does it look like to you?” Forster prodded. “How about frozen seawater?”
XIII

The
Michael Ventris
slowly settled out of orbit under the feathery tug of Amalthea’s gravity, until its flat tripod feet sank deep into the frothy surface. In the equipment bay the ice mole hung lightly in its shackles, lit by the metallic glare of worklights. Blake and Forster pulled themselves into its cockpit and methodically strapped themselves in. The gin-gery professor was seething with impatience.

“Quaint old gadget,” Blake muttered placidly, regarding the gaudy display panel now lit up like a carnival midway. He fiddled interminably with the instruments while Forster, who had been edgy throughout the tedious pre-launch, grew increasingly tense.

“Got an
old
mole here, do we?” came Josepha Walsh’s hoarse and cheerful voice over the comm.

 

“This Old Mole’s still got plenty of get up and go,” Blake said at last. “Diagnostics give us a clean slate. Ready to launch.”

 

“Let’s get
on
with it,” Forster said.

 

“All set, Jo?” Blake said in the general direction of the mike.

 

For a moment there was silence on the commlink before Walsh replied. “That’s a roger. You may proceed.”

 

Blake brought the clear bubble down over their heads and sealed it. “Confirming full atmospheric pressure, no dis-cernible leaks.”

“You’ll be fine as long as you’ve got your E-units,” came Walsh’s reply. Against sudden pressure loss they wore emer-gency soft-suits, with the faceplates of their head-fitting helmets left open. The mole was of too early a vintage to be equipped for Artificial Reality suits, with which a pilot could feel wholly a part of the machine.

“I hardly think we’re going to die of depressurization,” Forster said sharply.

Blake gave him a quick glance. Perhaps it was the sense of separation, the need for layers of protection and inter-pretation between him and the environment, that made the professor so irritable. Perhaps he was reminded of his near-disastrous expedition to Venus.

“I’ll not hold you up any longer then,” said Walsh. The clamshell doors of the equipment bay peeled away—

 

—opening upon stars above and unearthly white mist below, and on the horizon a ruddy glow, Jupiter itself riding unseen beneath the moon’s edge.

The whine of a miniature electric crane conveyed itself through the grapple to the roof of the vehicle as the mole was lifted ever so slowly out of the hold and held poised, outside the ship. The whine ceased. There was a click as the last magnetic grapple let go. Then another click, as springs uncoiled and gently propelled the machine away from the ship. Almost but not quite weightless, the massive machine slowly began to drop, nose down. It fell a long time into the mists, like a sagging helium balloon, interminably.

An edge of the huge alien antenna came out of the milky whiteness on the port side. The
Ventris
had purposely dropped the mole beside the antenna, for here the ice sam-ples showed patches anomalously younger than Amalthea’s otherwise uniform age of a billion years.

Blake and Forster hardly felt the slow collision with the delicate ice when they hit the surface—but outside there were sudden snowdrifts, halfway up the cockpit window.

Above and behind them, barely visible through the frosty window, two white shapes gleamed like portly angels, drifting down the black sky—Hawkins and Groves, checking the fat, half-coiled electrical cables that would power the mole from the
Ventris
’s auxiliary power units. They did what they had to behind the ice mole, securing the cable attachments.

“Okay, you should be mobile,” came Hawkins’s jolly voice over the commlink. He had gotten over his awkward-ness in spacesuits; indeed, with a day’s practice he’d become quite the athlete of the vacuum.

 

“We’re all go here,” Blake reported to the
Ventris
.

 

“And all links look good on our boards,” said Walsh from the flight deck.

 

Forster said tensely, “You may go ahead when ready.”

 

Blake eased the pots forward.

Below them opposed twin bits began an intricate dance, slowly at first, then with rising speed. A cloud of ice crystals engulfed the mole. The top ten or twelve meters were spongy froth, then there was a bump, and the machine abruptly descended through a pocket of vacuum-pocked ice. Finally, with a screech, diamond-edged titanium blades engaged old, hard ice, and the mole began to drill straight into the heart of Amalthea.

Forster suddenly relaxed, releasing a long sigh, as if he’d been holding his breath. The center of Amalthea tugged at his heart, harder the closer he got to it—like gravity, the force of his obsession increased with decreasing distance from his goal. But at least he was moving as fast as he could toward the object of his desire.
The big screen in the middle of the console gave Blake and Forster a clear three-dimensional image of their sector of the moon’s structure—where they were and where they were going. Along with information from a year’s worth of passive observation by Space Board satellites, the results of the
Ventris
’s recent seismic studies had been fed into the mole’s data banks. Had Amalthea been anything but a thor-oughly surprising place, the image on the screen might have been unexpected. . . .

For over a century, since it was first photographed close up by the primitive robot probe
Voyager 1
, Amalthea had been thought to be low in volatile substances—certainly a reasonable hypothesis, for the moon had no atmosphere, was rigid, seemed inert. By contrast, its much larger neigh-bor, Io, was a moon so rubbery, so rich in mutable liquids and gases, that remarkable sulfur volcanoes had been in constant eruption somewhere upon its surface ever since they had been discovered by the same
Voyager 1
, the first artificial observer to reach Jupiter’s orbit and the first, upon returning images of Io to its controllers, to reveal that the Earth was not alone in the solar system in being geologi-cally active.

But Amalthea was in fact about as volatile as a small body can be, consisting almost entirely of water; yet even while bathed in Jupiter’s radiation belts and racked by the tidal forces of the giant—a planet so massive it fell not far short of self-ignition into a star, and thus had often been described as a failed rival to the sun—Amalthea had re-mained frozen solid.

It takes energy to keep water frozen when the surround-ings are hot. After all pertinent data had been fed into the
Ventris
’s computers it was learned that the apparent dis-crepancy in Amalthea’s energy budget was due not to anything so paltry as a leakage of electrical energy from its radio antennas but to the considerably larger output of what, for want of better name, the expedition called its “re-frigerator.”

A refrigerator is really a heater that heats one part of the thing to be cooled until it is hotter than its surroundings, moving heat from the source to a sink or a radiator. The dark red dust of classical Almathea made a fine radiator, a surface from which the moon could rid itself of the heat it removed from its underlying ice. Most of the heat loss was disguised in the flux of Jupiter’s radiation belts; for more than a hundred years no one had suspected that diminutive Amalthea was adding measurably to the total energy of the belts themselves.

But where was the source?

The Old Mole’s graphics program had its limits—one had to severely restrain it from pretending to more certainty than it really had, when the input was from soft data—so the computer-generated map only sketchily showed that a spheroid of uncertain composition and dimension lay in the core of the moon. For a billion years, presumably, this object had produced the energy necessary to keep Amalthea frozen solid.

A year ago Amalthea had begun to unfreeze. But the moon was melting far faster than radiation belts or tidal forces could account for. Amalthea was melting because the core object had increased its heat output by several orders of magnitude. The refrigerator had turned into a stove.
This was what the seismologically generated map of Amalthea on the console displayed: a rind of solid ice, pierced by vents of gas and liquid, its surface subliming into vacuum. A mantle of liquid water, thirty kilometers deep. A core of hard, hot matter, composition unknown, but hot enough to boil the water that touched it.