The professor described the suggestion that the Lunarians might also be natives of Minerva as "ludicrous."

Despite a wealth of new information, therefore, much remains to be explained about recent events in the Solar System. Almost certainly, the next twelve months will see further exciting developments.

(See also the Special Supplement by our Science Editor on page 14.)

Captain Hew Mills, UN Space Arm, currently attached to the Solar System Exploration Program mission to the moons of Jupiter, stood gazing out of the transparent dome that surmounted the two-story Site Operations Control building. The building stood just clear of the ice, on a rocky knoll overlooking the untidy cluster of domes, vehicles, cabins, and storage tanks that went to make up the base he commanded. In the dim gray background around the base, indistinct shadows of rock buttresses and ice cliffs vanished and reappeared through the sullen, shifting vapors of the methane-ammonia haze. Despite his above-average psychological resilience and years of strict training, an involuntary shudder ran down his spine as he thought of the thin triple wall of the dome-all that separated him from this foreboding, poisonous, alien world, cold enough to freeze him as black as coal and as brittle as glass in seconds. Ganymede, largest of the moons of Jupiter, was, he thought, an awful place.

"Close-approach radars have locked on. Landing sequence is active. Estimated time to touchdown: three minutes, fifty seconds." The voice of the duty controller at one of the consoles behind Mills interrupted his broodings.

"Very good, Lieutenant," he acknowledged. "Do you have contact with Cameron?"

"There’s a channel open on screen three, sir."

Mills moved around in front of the auxiliary console. The screen showed an empty chair and behind it an interior view of the low-level control room. He pressed the call button, and after a few seconds the face of Lieutenant Cameron moved into the viewing angle.

"The brass are due in three minutes," Mills advised. "Everything okay?"

"Looking good, sir."

Mills resumed his position by the wall of the dome and noted with satisfaction the three tracked vehicles lurching into line to take up their reception positions. Minutes ticked by.

"Sixty seconds," the duty controller announced. "Descent profile normal. Should make visual contact any time now."

A patch of fog above the landing pads in the central area of the base darkened and slowly materialized into the blurred outline of a medium-haul surface transporter, sliding out of the murk, balanced on its exhausts with its landing legs already fully extended. As the transporter came to rest on one of the pads and its shock absorbers flexed to dispose of the remaining momentum, the reception vehicles began moving forward. Mills nodded to himself and left the dome via the stairs that led down to ground level.

Ten minutes later, the first reception vehicle halted outside the Operations Control building and an extending tube telescoped out to dock with its airlock. Major Stanislow, Colonel Peters, and a handful of aides walked through into the outer access chamber, where they were met by Mills and a few other officers. Mutual introductions were concluded, and without further preliminaries the party ascended to the first floor and proceeded through an elevated walkway into the adjacent dome, constructed over the head of number-three shalt. A labyrinth of stairs and walkways brought them eventually to number-three high-level airlock anteroom. A capsule was waiting beyond the airlock. For the next four minutes they plummeted down, down, deep into the ice crust of Ganymede.

They emerged through another airlock into number-three low-level anteroom. The air vibrated with the humming and throbbing of unseen machines. Beyond the anteroom, a short corridor brought them at last to the low-level control room. It was a maze of consoles and equipment cubicles, attended by perhaps a dozen operators, all intent on their tasks. One of the longer walls, constructed completely from glass, gave a panoramic view down over the workings in progress outside the control room. Lieutenant Cameron joined them as they lined up by the glass to take in the spectacle beyond.

They were looking out over the floor of an enormous cathedral, over nine hundred feet long and a hundred feet high, hewn and melted out of the solid ice. Its rough-formed walls glistened white and gray in the glare of countless arc lights. The floor was a litter of steel-mesh roadways, cranes, gantries, girders, pipes, tubes, and machinery of every description. The left-side wall, stretching away to the far end of the tunnel, carried a lattice of ladders, scaffolding, walkways, and cabins that extended up to the roof. All over the scene, scores of figures in ungainly heavy-duty spacesuits bustled about in a frenzy of activity, working in an atmosphere of pressurized argon to eliminate any risk of explosion from methane and the other gases released from the melted ice. But all eyes were fixed on the right-hand wall of the tunnel.

For almost the entire length, a huge, sweeping wall of smooth, black metal reared up from the floor and curved up and over, out of sight above their heads to be lost below the roof of the cavern. It was immense-just a part of something vast and cylindrical, lying on its side, the whole of which must have stretched far down into the ice below floor level. At the near end, outside the control room, a massive, curving wing flared out of the cylinder and spanned the cavern above their heads like a bridge, before disappearing into the ice high on the far left. At intervals along the base of the wall, where metal and ice met, a series of holes six feet or so across marked the ends of the network of pilot tunnels that had been driven all around and over and under the object.

It was far larger than a Vega. How long it had lain there, entombed beneath the timeless ice sheets of Ganymede, nobody knew. But the computations of field-vector resultants collected from the satellites had been right; there certainly had been something big down here-and it hadn’t been just ore deposits.

"Ma-an," breathed Stanislow, after staring for a long time. "So that’s it, huh?"

"That is big!" Peters added with a whistle. The aides echoed the sentiments dutifully.

Stanislow turned to Mills. "Ready for the big moment, then, Captain?"

"Yes, sir," Mills confirmed. He indicated a point about two hundred feet away where a group of figures was gathered close to the wall of the hull, surrounded by an assortment of equipment. Beside them a rectangular section of the skin about eight feet square had been cut away. "First entry point will be there- approximately amidships. The outer hull is double layered; both layers have been penetrated. Inside is an inner hull…" For the benefit of the visitors, he gestured toward a display positioned near the observation window showing the aperture in close-up.

"Preliminary drilling shows that it’s a single layer. The valves that you can see projecting from the inner hull were inserted to allow samples of the internal atmosphere to be taken before opening it up. Also, the cavity behind the access point has been argon-flooded."

Mills turned to Cameron before going on to describe further details of the operation. "Lieutenant, carry out a final check of communications links, please."

"Aye, aye, sir." Cameron walked back to the supervisory console at the end of the room and scanned the array of screens.

"Ice Hole to Subway. Come in, please."

The face of Commander Stracey, directing activities out near the hull, moved into view, encased in its helmet. "All checks completed and go," he reported. "Standing by, ready to proceed."