The Solar System is more than the backdrop to humanity’s successive civilizations: its fuel supplies shape political power, its planets become objects of exploration and settlement, and changes in the Sun and planetary orbits ultimately force humanity to seek a new home. Across the book, the same system shifts from an apparently inexhaustible storehouse to a fragile habitat whose survival depends on both human decisions and forces beyond human control.

An arena of rivalry and dependence

In the earlier history, struggles within the Solar System’s human societies are tied to resources distributed across the planet. Russia’s industrial development depends increasingly on American finance, while Germany and the United States compete for access to Russian oil. Because oil is becoming more valuable as a source of power, and supplies are limited, control of the remaining fields becomes a cause of political friction and war. The planetary setting is already an interconnected economic system: financial influence and the pursuit of fuel link distant regions, even as governments cast their conflicts in national or ideological terms.

This entanglement persists as the political order changes. After the Anglo-French War, European nations form a confederacy and pool their armaments, but Russia remains outside it; the United States interprets the arrangement as directed against itself and withdraws from the League of Nations, while China stays within. Later, control of fuel becomes a further test of international cooperation. The League imposes cosmopolitan oversight on oil and coal, but new fuel deposits in Antarctica fall outside the World Fuel Control Board’s jurisdiction. The United States moves to exploit them, while China calls for the deposits to be brought under shared control. The Solar System’s resources, in these episodes, are not just things to be extracted: where they lie, who can claim them, and which institutions govern them help determine whether political unity holds.

Energy and the limits of civilization

The First World State inherits a civilization powered largely by coal. After its founding, a new oil supply is exhausted in less than three centuries, requiring aircraft to run on electricity generated from coal. The resulting awareness of scarcity encourages conservation and experiments with wind, water, volcanic heat, and subterranean heat. These alternatives supplement the coal rather than replace it; the civilization’s power system remains dependent on Antarctic seams whose apparent abundance encourages a false confidence in their permanence.

That confidence breaks when even the deepest borings fail to reveal further deposits. The First World State’s collapse follows the sudden failure of coal supplies that had sustained it for thousands of years. The crisis is not simply a shortage of energy: the society’s religious commitment to ritual flight makes it politically difficult to cut a major drain on power, while its ruling flying aristocracy has reason to resist doing so. A resource limit that might have prompted a change in priorities instead exposes how thoroughly custom and authority have come to govern the use of the Solar System’s remaining fuel.

A later civilization discovers another way to release energy. After roughly five hundred years of intermittent research, Patagonian scientists learn to annihilate the positive and negative charges in a particular, uncommon kind of atom, using a large initial expenditure of energy. The resulting source is described as inexhaustible, readily controlled, and nevertheless not foolproof. The danger of its misuse gives the discovery a political and ethical consequence beyond its technical achievement. In a later scientific meeting, a young Chinese scientist demonstrates a rifle-like instrument that can initiate matter annihilation at a distance and in a precise direction, as well as inhibit the process. The scientists unanimously order the instrument and all accounts of its operation destroyed. Their decision makes the Solar System’s future hinge not only on what energy can do, but on whether those who possess its means can be trusted to use it.

From planetary home to navigable space

For the Fifth Men, abundant power transforms everyday life and makes travel through space increasingly practicable. Their material economy is run by mechanisms and self-regulating machinery; once routine labor is removed, research, invention, and design occupy human attention. Individual mobility extends beyond flight through the atmosphere: people can travel in wingless aerial boats or flight overalls, and the wider ambition is to adapt humanity to another world or adapt another world to humanity.

Early voyages show how difficult that ambition is. A pioneer vessel sent toward the Moon is lost after its messages cease and observers detect a flash along its course, leading people on the Terrestrial homeworld to suspect a meteor collision. Other trial craft fail in different ways: some lose control, one crashes during a lunar landing and loses its air, and crews endure suffocation or the effects of confinement. Later, as accidents become rarer, voyages through space turn into a popular amusement. Travellers pass close to the visible remains of civilization on Mars, search through Venus’s clouds for islands in its almost coastless ocean, and attempt journeys toward Mercury and beyond. Navigation itself becomes possible, but inhabiting another planet remains the harder problem.

The dark body and humanity’s departure

The Eighth Men detect signs that the Sun will eventually collapse into a White Dwarf and estimate that the process will begin in twenty thousand years. They plan to migrate to Mercury, which is expected to become less intolerably hot, and to prepare it with an atmosphere and a species able to adapt to extreme cold. Before that project can solve the danger, astronomers detect a non-luminous body of gas approaching the Solar System on a course that will intersect the Sun. Their calculations predict that the Sun will flare and expand so greatly that life will be impossible on nearly all the planets; Neptune may be the best remaining possibility, but it is cold, has unsuitable atmospheric conditions, and imposes an intolerable gravitational burden on human bodies.

The Eighth Men nevertheless prepare a successor species for Neptune. Specially designed vegetation is sent ahead to make a warm region more suitable for human use, and the Ninth Men are transported there, since the giant Eighth Men cannot endure Neptune’s pressure and gravity outside their ether-ships except briefly in steel diving suits. The wider catastrophe then transforms the planetary system: after the dark body narrowly misses Neptune, it engulfs Saturn with its rings and satellites, tangles planetary orbits, catches the Terrestrial homeworld and Venus in its blazing wake, and finally leaps at the Sun. The system’s center becomes a star nearly as wide as Mercury’s former orbit.

A setting that changes the meaning of home

The Solar System’s history links apparently separate kinds of crisis. Competition over oil and coal makes planetary geography a source of political power; technological abundance expands movement beyond the homeworld; and astronomical upheaval makes even successful settlement precarious. The migration to Neptune does not end that vulnerability, but marks humanity’s attempt to carry life and civilization through a transformed system. In this long perspective, the planets are neither fixed territories nor interchangeable destinations: each offers particular possibilities and limits, and each new home must be judged against the changing conditions of the whole system.