And now, out among the stars, evolution was driving toward new goals. The first explorers of Earth had long since come to the limits of flesh and blood; as soon as their machines were better than their bodies, it was time to move. First their brains, and then their thoughts alone, they transferred into shining new homes of metal and of plastic.

In these, they roamed among the stars. They no longer built spaceships. They were spaceships.

But the age of the Machine-entities swiftly passed. In their ceaseless experimenting, they had learned to store knowledge in the structure of space itself, and to preserve their thoughts for eternity in frozen lattices of light. They could become creatures of radiation, free at last from the tyranny of matter.

Into pure energy, therefore, they presently transformed themselves; and on a thousand worlds, the empty shells they had discarded twitched for a while in a mindless dance of death, then crumbled into rusty

Now they were lords of the galaxy, and beyond the reach of time. They could rove at will among the stars, and sink like a subtle mist through the very interstices of space. But despite their godlike powers, they had not wholly forgotten their origin, in the warm slime of a vanished sea.

And they still watched over the experiments their ancestors had started, so long ago.

"The air in the ship is getting quite foul, and I have a headache most of the time. There's still plenty of oxygen, but the purifiers never really cleaned up all the messes after the liquids aboard started boiling into vacuum. When things get too bad, I go down into the garage and bleed off some pure oxygen from the pods.

"There's been no reaction to any of my signals, and because of my orbital inclination, I'm getting slowly farther and farther away from TMA-2. Incidentally, the name you've given it is doubly inappropriate – there's still no trace of a magnetic field.

"At the moment my closest approach is sixty miles; it will increase to about a hundred as Japetus rotates beneath me, then drop back to zero. I'll pass directly over the thing in thirty days – but that's too long to wait, and then it will be in darkness, anyway.

"Even now, it's only in sight for a few minutes before it falls below the horizon again. It's damn frustrating – I can't make any serious observations.

"So I'd like your approval of this plan. The space pods have ample delta vee for a touchdown and a return to the ship. I want to go extravehicular and make a close survey of the object. If it appears safe, I'll land beside it – or even on top of it.

"The ship will still be above my horizon while I'm going down, so I won't be out of touch for more than ninety minutes.

'Tm convinced that this is the only thing to do. I've come a billion miles – I don't want to be stopped by the last sixty."

For weeks, as it stared forever Sunward with its strange senses, the Star Gate had watched the approaching ship. Its makers had prepared it for many things, and this was one of them. It recognized what was climbing up toward it from the warm heart of the Solar System.

If it had been alive, it would have felt excitement, but such an emotion was wholly beyond its powers. Even if the ship had passed it by, it would not have known the slightest trace of disappointment. It had waited three million years; it was prepared to wait for eternity.

It observed, and noted, and took no action, as the visitor checked its speed with jets of incandescent gas. Presently it felt the gentle touch of radiations, trying to probe its secrets. And still it did nothing.

Now the ship was in orbit, circling low above the surface of this strangely piebald moon. It began to speak, with blasts of radio waves, counting out the prime numbers from 1 to 11, over and over again. Soon these gave way to more complex signals, at many frequencies-ultraviolet, infrared, X rays. The Star Gate made no reply; it had nothing to say.

There was a long pause, then, before it observed that something was falling down toward it from the orbiting ship. It searched its memories, and the logic circuits made their decisions, according to the orders given them long ago.

Beneath the cold light of Saturn, the Star Gate awakened its slumbering powers.

Discovery looked just as he had last seen her from space, floating in lunar orbit with the Moon taking up half the sky. Perhaps there was one slight change; be could not be sure, but some of the paint of her external lettering, announcing the purpose of various hatches, connections, umbilical plugs, and other attachment, had faded during its long exposure to the unshielded Sun.

That Sun was now an object that no man would have recognized. It was far too bright to be a star, but one could look directly at its tiny disk without discomfort. It gave no heat at all; when Bowman held his ungloved hands in its rays, as they streamed through the space pod's window, he could feel nothing upon his skin. He might have been trying to warm himself by the light of the Moon; not even the alien landscape fifty miles below reminded him more vividly of his remoteness from Earth.

Now he was leaving, perhaps for the last time, the metal world that had been his home for so many months. Even if he never returned, the ship would continue to perform its duty, broadcasting instrument readings back to Earth until there was some final, catastrophic failure in its circuits.

And if he did return? Well, he could keep alive, and perhaps even sane, for a few more months. But that was all, for the hibernation systems were useless with no computer to monitor them. He could not possibly survive until Discovery II made its rendezvous with Japetus, four or five years hence.

He put these thoughts behind him, as the golden crescent of Saturn rose in the sky ahead. In all history, he was the only man to have seen this sight. To all other eyes, Saturn had always shown its whole illuminated disk turned full toward the Sun. Now it was a delicate bow, with the rings forming a thin line across it – like an arrow about to be loosed, into the face of the Sun itself.

Also in the line of the rings was the bright star of Titan, and the fainter sparks of the other moons. Before this century was half gone, men would have visited them all; but whatever secrets they might hold, he would never know.

The sharp-edged boundary of the blind white eye was sweeping toward him; there was only a hundred miles to go, and he would be over his target in less than ten minutes. He wished that there was some way of telling if his words were reaching Earth, now an hour and a half away at the speed of light. It would be the ultimate irony if, through some breakdown in the relay system, he disappeared into silence, and no one ever knew what had happened to him.

Discovery was still a brilliant star in the black sky far above. He was pulling ahead as he gained speed during his descent, but soon the pod's braking jets would slow him down and the ship would sail on out of sight – leaving him alone on this shining plain with the dark mystery at its center.

A block of ebony was climbing above the horizon, eclipsing the stars ahead. He rolled the pod around its gyros, and used full thrust to break his orbital speed. In a long, flat arc, he descended toward the surface of Japetus.

On a world of higher gravity, the maneuver would have been far too extravagant of fuel. But here the space pod weighed only a score of pounds; he had several minutes of hovering time before he would cut dangerously into his reserve and be stranded without any hope of return to the still orbiting Discovery. Not, perhaps, that it made much difference...