The Gentle Giants of Ganymede

'Incredible,' Hunt agreed. 'I #146;ve never had a chance to talk about that kind of thing with them. . . not yet anyway.'

'Oh, yes.' Danchekker nodded. 'They were extremely proficient genetic engineers, were our Ganymean friends. . . very proficient.'

Hunt thought for a second and then snapped his fingers in sudden comprehension.

'But of course,' he said. 'In doing that they buggered their CO2 tolerance too.'

'Precisely, Vic. All the other animals on Minerva retained the high natural tolerance. Only the Ganymeans were different; they sacrificed it in exchange for accident-resistance.'

'But I don #146;t see how they could,' Hunt said, frowning again. 'I mean, I can see how they did it, but I don #146;t see how they could get away with it. They must have needed the CO2 tolerance, otherwise they wouldn #146;t have evolved it in the first place. They must have known that too. Surely they weren #146;t stupid.'

Danchekker nodded as if he already knew what Hunt was going to say.

'That probably wasn #146;t so obvious at the time,' he said. 'You see, the composition of the Minervan atmosphere fluctuated through the ages much the same as that of Earth has. From various researches the Ganymeans established that at the time land life first emerged, volcanic activity was at a peak and the level of CO2 was very high; naturally, therefore, the earliest species developed a high resistance. But as time went on the level decreased progressively and appeared to have stabilized itself by the time of the Ganymeans. They came to regard their tolerance mechanism as an ancient relic of conditions that no longer existed and their experiences showed that they could get by without it. The margin was small #151;the CO2 level was still high by our standards #151;but they could manage. So, they decided to do away with it permanently.'

'Ah, but then the level started going up again,' Hunt guessed.

'Suddenly and catastrophically,' Danchekker confirmed. 'On a geological time scale anyway. They were in no immediate danger, but all their measurements and calculations indicated that if the rate of increase went on, they #151;or their descendants one day anyway #151;would be in trouble. They would be unable to survive without their ancient tolerance mechanism, but they had eliminated that mechanism from their race. All the other animals would have no difficulty in adapting, but the Ganymeans were somewhat stuck.'

The full magnitude of the problem that had confronted the Ganymeans dawned on Hunt at last. They had bought a one-way ticket out of the hard-labor camp only to find that it led to the death cell.

'What could they do?' Danchekker asked, and then went on to answer the question for himself. 'First #151;use their technology to hold the CO2 level down by artificial means. They thought of that but their models couldn #146;t guarantee them a tight enough measure of control over the process. There was a high risk that they #146;d end up freezing the whole planet solid and, being the cautious breed that they were, they elected not to try it #151;at least not until it was a last-resort measure.

'Second #151;they could reduce the CO2 as before, but have ready at hand a method for warming up the Sun to compensate for the loss of the greenhouse effect if the atmospheric engineering got out of control. They tried that on Iscaris but it went wrong, as the scientists on Minerva learned when they received a message from the Shapieron that was sent just before the ship itself got away.'

Hunt made no move to interrupt, so Danchekker continued. 'Third #151;they could migrate to Earth. They tried doing so on a pilot scale, but that went wrong too.' Danchekker shrugged and held the posture, his arms extended to indicate that he had run out of possibilities. Hunt waited for a moment longer, but the professor evidently had nothing more to say.

'So what the devil did they do?' Hunt asked.

'I don #146;t know. The Ganymeans don #146;t know either, since whatever else may have been thought of was thought of after they had left Minerva. They are as curious as we are #151;more so I would imagine. It was their world.'

'But the animals from Earth,' Hunt insisted. 'They were all imported later on. Couldn #146;t they have had something to do with the solution?'

'They could have, certainly, but what exactly, I #146;ve no idea. Neither have the Ganymeans. We #146;re satisfied, though, that it would not have been anything to do with using a terrestrial type of ecology to absorb the CO2 . That simply wouldn #146;t have worked.'

'That idea #146;s gone right out the window, eh?'

'Right out,' Danchekker said decisively. 'Why they brought the animals there and whether or not it had anything to do with their atmospheric problem is still all a mystery. . . .' The professor paused and peered intently over the top of his spectacles. 'There #146;s another mystery too now #151;a new one #151;from what we #146;ve just been talking about.'

'Another one?' Hunt returned his stare curiously. 'What?'

'All the other Minervan animals,' Danchekker replied slowly. 'You see, if they all possessed a perfectly adequate mechanism for dealing with CO2 , it couldn #146;t have been the changing atmosphere of Minerva that wiped them all out after all. If that didn #146;t, then what did?'

Chapter Fourteen

The landscape was a featureless, undulating sheet of ice that extended in every direction to merge into the gloom of a perpetual night. Overhead a diminutive Sun, barely more than just a bright star among millions, sent down its feeble rays to paint an eerie and foreboding twilight on the scene.

The huge shadowy shape of the ship soared upward to lose itself in the blackness above; arc lights set high on its side cast down a brilliant cone of whiteness, etching out an enormous circle on the ice next to where the ship stood. Around the inside of the periphery of the pool of light, several hundred spacesuited, eight-foot-tall figures stood four deep in unmoving ranks, their heads bowed and their hands clasped loosely before them. The area within the circle was divided into a series of concentric rings and at regular intervals around each ring rectangular pits had been cut into the ice, each one aligned with the center. By the side of each of the pits lay a metallic, box-shaped container roughly nine feet long and four feet wide.

A small group of figures walked slowly to the center and began moving around the innermost ring, stopping at each pit in turn and watching in silence while the container was lowered before moving on to the next. A second small group followed, filling each of the pits with water from a heated hose; the water froze solid in seconds. When they had finished the first ring they moved out to begin on the second, and continued until they were back at the edge of the circle.

They stood gazing for a long time at the simple memorial that they had erected in the center of the circle #151;a golden obelisk with an inscription on each face, surmounted by a light that would burn for a hundred years. And as they gazed, their thoughts went back in time to friends and faces that they once had known, and who could never again be more than memories.

Then, when the time had come, they turned away and began filing slowly back toward their ship. When the arc lights were turned out, only the tiny glow of light around the obelisk remained to hold the night at bay.

They had honored the pledge that they had made and carried with them through all the years that had brought them here, from another place, from another time.

Beneath the ice field of Pluto lay the soil of Minerva.

The Giants had come home to lay their dead to rest.

Chapter Fifteen

The Shapieron reappeared out of space as suddenly as it had gone. The surveillance radars of Jupiter Five picked up an indistinct echo hurtling in from the void and rapidly consolidating itself as it shed speed at a phenomenal rate. By the time the optical scanners had been brought to