The Sentinel - Arthur C. Clarke [60]
“Not to Jupiter!” I gasped.
“Heavens no, nothing as drastic as that! But we’re going nearer to him than anyone else has ever been.”
He paused thoughtfully.
“It’s a curious thing, you know—or you probably don’t—that it’s nearly as difficult to travel between Jupiter’s satellites as it is to go between the planets, although the distances are so much smaller. This is because Jupiter’s got such a terrific gravitational field and his moons are traveling so quickly. The innermost moon’s moving almost as fast as Earth, and the journey to it from Ganymede costs almost as much fuel as the trip from Earth to Venus, even though it takes only a day and a half.
“And it’s that journey which we’re going to make. No one’s ever done it before because nobody could think of any good reason for the expense. Jupiter Five is only thirty kilometers in diameter, so it couldn’t possibly be of much interest. Even some of the outer satellites, which are far easier to reach, haven’t been visited because it hardly seemed worth while to waste the rocket fuel.”
“Then why are we going to waste it?” I asked impatiently. The whole thing sounded like a complete wild-goose chase, though as long as it proved interesting, and involved no actual danger, I didn’t greatly mind.
Perhaps I ought to confess—though I’m tempted to say nothing, as a good many others have done—that at this time I didn’t believe a word of Professor Forster’s theories. Of course I realized that he was a very brilliant man in his field, but I did draw the line at some of his more fantastic ideas. After all, the evidence was so slight and the conclusions so revolutionary that one could hardly help being skeptical.
Perhaps you can still remember the astonishment when the first Martian expedition found the remains not of one ancient civilization, but of two. Both had been highly advanced, but both had perished more than five million years ago. The reason was unknown (and still is). It did not seem to be warfare, as the two cultures appear to have lived amicably together. One of the races had been insect-like, the other vaguely reptilian. The insects seem to have been the genuine, original Martians. The reptile-people—usually referred to as “Culture X”—had arrived on the scene later.
So, at least, Professor Forster maintained. They had certainly possessed the secret of space travel, because the ruins of their peculiar cruciform cities had been found on—of all places—Mercury. Forster believed that they had tried to colonize all the smaller planets—Earth and Venus having been ruled out because of their excessive gravity. It was a source of some disappointment to the Professor that no traces of Culture X had ever been found on the Moon, though he was certain that such a discovery was only a matter of time.
The “conventional” theory of Culture X was that it had originally come from one of the smaller planets or satellites, had made peaceful contact with the Martians—the only other intelligent race in the known history of the System—and had died out at the same time as the Martian civilization. But Professor Forster had more ambitious ideas: he was convinced that Culture X had entered the Solar System from interstellar space. The fact that no one else believed this annoyed him, though not very much, for he is one of those people who are happy only when in a minority.
From where I was sitting, I could see Jupiter through the cabin porthole as Professor Forster unfolded his plan. It was a beautiful sight: I could just make out the equatorial could belts, and three of the satellites were visible as little stars close to the planet. I wondered which was Ganymede, our first port of call.
“If Jack will condescend to pay attention,” the Professor continued, “I’ll tell you why we’re going