"Oldest of all the eight worlds of this solar system, indeed, is our world of Neptune. This you must know, indeed, if your scientists know aught of the formation of the sun's planets. For those eight planets were formed unthinkable eons ago, out of the fiery sun itself. Up to that time the sun had moved through space entirely without planets, one of the countless stars of this galaxy of stars, all moving through the void in differing directions. One of these other stars chanced to be moving in the general direction of our own star, our own sun, and their mutual attraction for each other drew them closer together, until at last they passed each other closely, perhaps even touched each other, their nearness to each other causing by gravitational attraction huge masses of the flaming gaseous substance of each to break loose. Thus the space between the two passing suns was filled with those great flaming masses, and as they separated, each by its gravitational power drew a share of those fiery masses with it on its path through the void.
"Thus when the two suns receded from each other once more, each carried with it a rough half of the fiery masses that had been torn from each. As the sun moved on through space with these fiery masses about it, the greater part of them dropped back into the sun. The flaming masses that remained, however, had been thrown by the cataclysm into a swift motion, which by the sun's attraction had been converted in the case of each flaming mass into a circular or elliptical orbit around the sun. And since the speed of each flaming mass just balanced with its centrifugal force the pull of the sun inward, they continued in those orbits for age on age without perceptible change. The solar system, then, had become stable.
"Thus the sun was moving out through space with eight great flaming masses of matter revolving around it, in addition to a number of great clouds or aggregations of smaller fragments. These eight flaming masses became in time the sun's eight worlds, a solid crust forming first on one and then on another of them. The outermost of these great fiery masses was that which in time was to become the planet Neptune. It had been one of the first of the great fragments of the two suns torn loose by their encounter, and being one of the first had been hurled out to a greater distance than any of the others. And being the first, too, it had had more time to cool, its solid crust had formed earlier on it, and thus Neptune was in fact the oldest of the sun's planets to form as a solid-surfaced world. Neptune, too, is composed of much lighter materials than the denser inner planets, and the reason for that is, that it was the lighter matter of the two suns that had naturally been sent flying forth from them in their encounter; and thus the outer planets, the four great outer worlds, being of the sun's lighter matter, are all much less in density than the four smaller inner worlds, which were thrown forth later from the sun's heavier matter, and thus in smaller masses.
"So out of the great irregular-shaped outermost mass of flaming gases had been formed the great planet Neptune and its smaller moon of Triton. And as Neptune's surface solidified, as the great masses of water-vapor and air that made up its dense and immense atmosphere ensheathed it, it became a habitable world, one fit for life and the continuation of life. For though small heat came to distant Neptune across the great void of almost three billion miles that separated it from the sun, the sun giving it indeed a heat hardly perceptible, yet there was heat enough for the great world in its own fiery interior. For so great in size was Neptune that, though a solid crust had formed upon it, there still lay beneath that crust the vast raging fires of its interior, and those fires' heat was so great that they kept the surface of Neptune and the dense atmosphere above that surface warmed constantly. And Triton had an atmosphere also and interior warming fires.
"Thus great Neptune, though farthest of all planets from the sun, became habitable the earliest of all. And since, wherever a world is found on which life is possible, life sooner or later will arise, so it arose on Neptune. Race upon race of living creatures rose upon it, and race after race vanished, annihilated by changing conditions on its surface which they could not withstand. It was not until we disk-bodied Neptunians evolved upon the great world's surface, indeed, that there came a permanent form of life upon it. For we, whose disk-bodies owed their squat, flat shapes to the gravitational power of Neptune, so much greater than that of your inner worlds, had in larger measure that spark of intelligence which the other creatures had lacked. And with that gleam of mind, of intelligence, we were able to withstand the changing conditions on Neptune's surface by adapting ourselves to those conditions, growing ever in numbers and spreading out over our world's surface, until at last we swarmed in millions upon it and were rising into greater and greater comprehension of the universe about us, into greater and greater intelligence and power.
"Great buildings we built upon Neptune's surface, and deep we tunnelled below its surface, also. Through breaks in the great cloud-screen about our world we looked forth and saw with our instruments the other planets that moved about our sun, and looked forth also into space and saw the hosts of other suns that moved at vast distances from our own. Our eyes were accustomed to the dim Neptunian day, our bodies to its great gravitational power, and it was our home-world. Yet by this time so vast had become our numbers that millions of us were crowded too closely together, and desired to migrate to Triton, our moon, and settle there. And though we had never yet been able to sally forth from the surface of our own great world of Neptune, we found the way to do so then.
"That way was given to us by the discovery by our scientists of a new force-vibration, one that lay in wavelength between the light vibrations and the higher electrical vibrations. This force-vibration, they found, exerted a definite pressure or force upon any object struck by its waves, just as the light rays themselves exert a definite, though far smaller, pressure upon whatever matter they strike. With this new force-ray, therefore, we planned to propel vehicles through space, and we constructed great cylindrical vehicles which were to hurtle out into space by generating inside them a great force-ray which would be shot back against a world and thus propel them by repulsion away from that world. These cylinders were made and tested, and since they worked perfectly, we constructed many of them, enough to take out all the millions of our surplus population to Triton. And so in those cylinders those millions of Neptunians went hurtling out to Triton.
"They found, as our observations had shown us, that Triton had a good atmosphere, and that it was swarming already with many forms of life, some of them unutterably grotesque, and none of more than the lowest intelligence. Using weapons of concentrated force-rays, which clove through all they touched, our millions of Neptunians proceeded to annihilate all life upon Triton, and with that accomplished, proceeded to build for themselves structures and cities like those on Neptune. They found that Triton was a perfectly habitable world for them save for two considerations. One of these was the lesser gravitational power of it, which made it extremely inconvenient for them to move on it with their Neptunian muscles. They solved this problem by attaching to their limbs small and unobtrusive disks of an extremely heavy metal which we could make by the artificial massing of atom-protons without electrons. These disks increased their weight to such a point that they could move as freely and conveniently on Triton as on Neptune.
"The other problem facing them on Triton was the fact that it turned one face always toward the sun. Its rotation on its axis, indeed, was of just enough speed to counteract its revolution around Neptune and Neptune's own revolution around the sun, the sum total of its movements resulting in this keeping of one side always toward the sun, with that side always palely lit by the sun and the other always in darkness. Even when Triton was behind Neptune, invisible perhaps from your own world by reason of the edge of Neptune's great atmosphere projecting up to hide it somewhat, Triton's orbit was so slanted or inclined toward the plane of the solar system that the sun was always in sight of its sunward side, though dimmed a little when the edge of Neptune's atmosphere was between them. The Neptunians who had gone to Triton were accustomed to Neptune's alternating day and night, of approximately ten hours each, and so they solved the problem by living upon the sunlit side of Triton for ten hours, for a day, and then passing to the dark side for ten hours of night.