The craft approaching the system in 2031 did not know even these simple facts. Swimming in black vastness, it understood only that it was once again nearing a commonplace type of star and that the familiar ritual must begin again.
Though it was carrying out a long and labored exploration of this spiral arm, it had not chosen this particular star at random. Long before, cruising at a sizable fraction of light speed somewhat below the plane of the galaxy, it had filtered through the whispering radio noise a brief signal. The message was blurred and garbled. There were three common referents the craft could piece together, however, and these resembled an ancient code it had been taught to honor. The machine began to turn in a great arc which arrowed toward a grouping of stars; the jittery message had not lasted long enough to get a precise fix.
Much later, during the approach, a stronger radio burst peaked through the sea of hydrogen emission. A distress call. Life system failure. A breach in the hull, violation of the vital integrity indices—
There it ended. The signal’s direction was clearer. But did it come from this system ahead, or from some much more distant source lying behind it? In such circumstances the craft fell back on its habitual patterns.
Its first duty was simple. It had already decelerated until interstellar dust would no longer plow into it with blistering, destructive velocity. The craft could now safely cut off the magnetic fields encasing it and begin to extend sensors. A port opened to the utter cold and peered ahead. A blinder drew across the image of the nearing star, so that tiny flecks of light nearby could register.
The telescope employed was 150 centimeters in diameter and did not differ markedly from those used on Earth; some facets of design, bounded by natural law, are universal. The craft crept along at far below light speed. Isotopes met with a low mumble in the throat of its exhaust. Fingers of magnetic fields, extended forward, plucked the proper atoms from the interstellar gas and funneled them in. Only this carving of a cylinder in the dust disturbed the silent reaches.
The craft watched patiently. Any planets orbiting the star ahead were still far away, and picking out their movements against the speckled background of stationary stars was difficult. At four-tenths of a light-year away, the activated circuits and their consultation backup agreed: a yellow-brown patch near the white star was a planet. Higher functions of the computers felt the prickly stirrings of activity and heard of the discovery. A background library of planetary theory was consulted. The blurred, dim disk ahead shimmered as the ship swept through a whisper-thin cloud of dust, while the machine bracketed and measured its objective in methodical detail.
The planet was large. It might have enough mass to ignite thermonuclear fires in its core, but experience argued that its light was too weak. The computers pondered whether to classify the system as a binary star and eventually decided against it. Still, the waxing point of light ahead held promise.
The morning passed in puzzled argument.
Nigel wasn’t totally willing to abandon the hypothesis that Jupiter Monitor had malfunctioned. The flight engineers—a flinty crew, skeptical of nonspecialists, fond of jargon—thought otherwise. They gave ground grudgingly, pitting sweet cool reason against Nigel’s vague doubts. A complete run-through of J-Monitor’s error-detection modes, a new diagnostic analysis, a hand-check of transmissions—all showed nothing wrong. There was no mechanical flaw.
The quirky echo had faded away a little after 3
A.M.
The Monitor was no longer in its original ellipse around Jupiter; a month earlier its engines had stirred awake and fired, to nudge it into orbit around Callisto, fifth moon of Jupiter. Now it spun an elaborate orange-slice orbit, lacing over the icy glare of Callisto’s poles every eight hours.
Nigel snapped a cracker in half, swallowing it with some lukewarm tea, hardly noticing the mingling of sweet and tart. He closed his eyes to the
ting
and clatter of telemetry. The flight engineers had finally gone back to their burrows and he and Lubkin sat in the main control bay, at one of the semicircular tables; digital arrays ringed them.
“That puts paid to the simple ideas, then,” Nigel said. “I suppose we’d best have a glance at the Callisto orbit.”
“Don’t follow,” Lubkin said.
“If the signal came from a source
outside
J-Monitor, something cut it off. The echo must’ve faded because Callisto came between the source and J-Monitor.”
Lubkin nodded. “Reasonable. The same thing had occurred to me, but—” he looked at his watch. “It’s almost noon. Why didn’t the echo return around seven or so this morning, when J-Monitor came
out
from behind Callisto?”
Nigel had the uncomfortable feeling that he was playing the role of dull-witted graduate student to Lubkin’s learned professor. But then, he realized, that was precisely the impression a skillful administrator would try to create.
“Well … maybe the other source is occluded by Jupiter itself. Now
it’s
blotted out.”
Lubkin pursed his lips. “Maybe, maybe.”
“Can’t we rough out some sort of orbit for the source, given a triangulation with Callisto?”
Lubkin nodded.
Around every star stretches a spherical shell of space, and somewhere within the thickness of that shell, temperatures are mild. For an Earthlike world, given the right primordial nudge, water will be liquid on the planet’s surface.
One-third of a light-year from the burning nugget of the star, the craft surveyed this livable zone and found it good. There was no sign of a large planet like the yellow-brown gas giant circling further out. This was a crucial test, for a massive world, close in, would have made another stable orbit impossible within the life-giving volume. Had the ship found such a planet, it was under standing orders—encrusted, ingrained, so old they functioned as instincts—to accelerate through the system, gathering all possible data for the astrophysical index, and chart a course for the next in a lengthy record of candidate suns.
Instead, the ship quickened the rumble of deceleration. It uncapped its telescope more frequently and peered ahead for longer intervals. A blue-white splotch revolved into another gas giant planet, smaller than the first and further out. Its image resisted precise definition. The craft noted a blurred circlet of bluish light—the body was ringed, a not uncommon occurrence among heavy planets.
Another massive planet was found, thinly ringed, and then another, each further away from the star. The machines began lowering their estimates of the possibility of life in this system. Still, past experience held out a glimmer of hope. Small, dim worlds might lie further in, even if the weight of theory and observation made it seem unlikely. By a fluke, the ship could be approaching from the night side of a world and miss it entirely. The craft waited.
At one-sixth of a light-year out the computers found an ambiguous smear of blue and brown and white: a planet near the star. Reward circuits triggered. The machines felt a spasm of relief and joy, a seething electric surge within. They were sophisticated devices, webs of impulses programmed to want to succeed, yet buffered against severe disappointment if success eluded them.
For the moment they were content. The ship flew on.
Spherical trigonometry, the vectoring line of J-Monitor’s main dish, calculus, orbital parameters, estimates, angles. Check and recheck.
Slowly, the most probable answer emerged—3:30
P.M.
, an hour away. By then the source should arc into view of J-Monitor’s main dish. Nigel imagined it as a dot of light slowly separating from the churning brown bands of Jupiter, rising above the horizon. As it traced its own ellipse, J-Monitor would be surveying the snow fields of Callisto below with its own mechanical intensity; craters, wrinkled hill lines, fissures, glinting blue ice mountains.
“One hour,” Lubkin said.
“Can we realign the main dish that quickly, without disturbing the surveying routine?” Nigel asked.
“We’ll have to,” Lubkin replied firmly. He picked up the telephone and dialed Operations Control.
“Tell them to rotate the camera platform, too,” Nigel said quickly.
“You think there’ll be anything to see at that range?” Nigel shrugged. “Possibly.”
“The narrow-angle camera? We can’t move both in—” “Right. We should work out a set of shots. Use the filters, stepping down from ultraviolet to IR. They can sequence automatically.”
Lubkin began speaking rapidly and precisely into the telephone, smiling confidently now that there were orders to be given, men to be told.
The ship was still cruising in deep silence, far from the star’s warmth, when it began to discern radio waves. More of the higher functions of the craft came alive. The weak signals were weighed and sifted. Filtering away the usual sputtering star noise, they found a faint trace of emission localized to the planets.
The most powerful source was the innermost gas giant. This was an optimistic sign, for the world did orbit fairly near its star. If it had merely a transparent atmosphere it would be too cold, but analysis showed it to be cloaked in thick, deep clouds. Such planets could warm themselves, the ship knew, by gravitational contraction and by heat-trapping—the greenhouse effect. Life could well evolve in their skies and seas.
Still, such clotted blankets of gas and liquid meant awesome pressures. Life in similar worlds rarely developed skeletons and thus could not manipulate tools; the ship’s log carried many instances of this. Trapped in their deep bowl of ammonia and methane, free of technology’s snarls, such creatures could not communicate—and the ship could assuredly not fly into such pressures in search of them.
A smaller source of radio waves lay further inward. It was the third planet, blue and white. The signals wove complex overlapping patterns, faint tremors that could be atmospheric phenomena: thunderstorms, lightning flashes, perhaps radiation from a magnetosphere. Still, the world was wrapped in a clear gas, a hopeful sign. The craft flew sunward.
By 6
P.M.
they became discouraged. The Monitor’s main dish was reprogrammed to carry out a methodical search pattern around the spot where the unknown radio source should appear.
It was functioning. The data were coming in. All operations were proceeding smoothly.
And there were absolutely no results.
The flight engineering staff was milling about, writing day summary reports, ready to go home. To them, the echo problem was a temporary aberration that cleared up of itself. Until it reappeared, no cause for alarm.
The target should have emerged from Jupiter’s rim at 3:37
P.M.
, according to revised estimates. Given the time lag in signals from Jupiter, Operations Control began receiving data slightly before 4:30
P.M.
The main dish’s search was completed within an hour. They couldn’t use the narrow-angle camera—not enough technicians were free from the Mars Burrower and the planetary satellites. In any case, nothing indicated that there was anything worth seeing.
“Looks like balls-up on that,” Nigel said.
“Either the whole idea is a pipe dream—” Lubkin began.
“Or we haven’t got the orbit right,” Nigel finished. An engineer in portable headphones came down the curved aisle, asked Lubkin to sign a clipboard, and went away.
Lubkin leaned back in his roller chair. “Yeah, there’s always that.”
“We can have another go tomorrow.”
“Sure.” Lubkin did not sound particularly enthusiastic. He got up from the console and paced back and forth in the aisle. There wasn’t much room; he nearly bumped into a technician down the way who was checking readouts at the Antenna Systems console. Nigel ignored the background murmur of the Control Bay and tried to think. Lubkin paced some more and finally sat down. The pair studied their green television screens, which were tilted backward for ease of viewing, where sequencing and programming data were continually displayed and erased. Occasionally the computer index would exceed its allowed parameter range and the screen would jump from yellow-on-green to green-on-yellow. Nigel had never gotten used to this; he remained disconcertingly on edge until someone found the error and the screen reverted.
The console telephone rang, jarring his concentration still further. “There’s an external call for you,” an impersonal woman’s voice said.
“Put them off a bit, will you?”
“I believe it’s your wife.”
“Ah. Put her on hold.”
He turned to Lubkin. “I’d like to get the camera free tomorrow.”
“What’s the use?”
“Call it idle speculation,” he said shortly. He was rather tired and wasn’t looking for an argument.
“Okay, try it,” Lubkin said, threw down his pencil and labored to his feet. His white shirt was creased and wrinkled. In defeat he seemed more likable to Nigel, less an edgy executive measuring his moves before he made them. “See you tomorrow,” Lubkin said and turned away, shoulders slumped.
Nigel punched a button on the telephone.
“Sorry I took so long, I—”
“Nigel, I’m at Dr. Hufman’s.”
“What’s—”
“I, I need you here. Please.” Her voice was thin and oddly distant.
“What’s going?”