"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.