Within a few hours more Mars was behind us, its red sphere fading rapidly into a crimson spot of light to the left and behind. The planet's two tiny moons, Phobos and Deimos, we had not yet seen despite our nearness to it, but it was with something of regret that we saw the crimson world and all the strange mysteries that we felt existed upon it, dropping behind us. Neptune alone, as Marlin had said, was our goal, and on toward its calm green light-dot we were rushing. I turned off our side-ray, therefore, which was no longer needed to counteract Mars's pull, and we gave all our attention to the panorama ahead. Save for Neptune's distant green dot, the only planets now visible amid the brilliant hosts of stars before us were Jupiter and Saturn. Saturn was shining ever more brightly to the left, its strange ring-formation already becoming visible to our eyes. But it was Jupiter that now dominated all the scene before us, his mighty sphere, its oblateness plainly visible, moving in majestic white splendor at the center of his four great moons. It was not the planets ahead that held my attention now, though, as our throbbing flier raced onward, Mars and its orbit dropping behind. "The asteroids!" I exclaimed. "We're almost into their region now--will be among them soon!" "And they're one of the greatest perils we'll encounter," Marlin said. "Hold ready to the controls, Hunt, for if we crash into one it means our end--the end of Earth's chance!" * * * * * I did not need his admonition, though, to make me tense my hands upon the control-switches, gazing intently forward. I knew we were now passing into one of the most dangerous regions of all the solar system--that great belt of whirling asteroids that lies between the orbits of Mars and Jupiter. More than a thousand in number, ranging from the great sphere of Ceres, 480 miles in diameter, down to the smallest asteroids of a few miles diameter only, they whirled there around the sun between the four inner and four outer planets, their orbits a maze of interwoven circles and ellipses. The greater part of them were so small, indeed, that at the tremendous speed with which our space-flier was flashing on they could be seen only in the moment that we rushed upon them. And yet in that moment we must whirl aside from any before us, since otherwise, pulled closer by the asteroid's own gravitational power, we would infallibly crash into it and meet our doom.