The Solar System is the central inhabited and contested space of the narrative: the human world that the Trisolarans can observe, the object of humanity’s military preparations, and the setting in which technological hope repeatedly collides with ecological and political catastrophe. Its planets, moons, asteroids, and outer reaches become not merely astronomical locations but components of a civilization-wide defense system whose construction changes human society as profoundly as the approaching enemy does.

A Transparent and Vulnerable World

The Solar System first appears as a place whose apparent vastness offers no protection from surveillance. As additional Sophons continually enter the Solar System and reach Earth, the Trisolarans can observe human activity with complete openness. Every meeting room, file cabinet, computer memory, plan, deployment, and communication is exposed to the enemy command four light-years away as soon as it takes shape. The Solar System is therefore not simply under observation; it has become an entirely transparent strategic environment in which conventional secrecy is impossible.

That transparency creates an unusual asymmetry. The Trisolarans communicate through direct, open thoughts and are consequently deficient in tricks, camouflage, and deception, while humanity retains an advantage in strategic concealment and indirect planning. This condition gives rise to the Wallfacer Project, whose plans must remain hidden inside human minds rather than in documents or communications. The Solar System thus becomes the physical stage for an information war in which location matters less than who can preserve an inner space inaccessible to the Sophons.

The vulnerability of the Solar System is also rendered on a human scale aboard Judgment Day. At night, Mike Evans stands on the bow while the Pacific slips past beneath the sky, using the Sophon’s text on his retinas to converse with the distant world. The scene joins the terrestrial sea to an interstellar exchange: the Solar System appears peaceful and open, yet its surface is already threaded by communication with an adversarial civilization. Evans’s twenty-second real-time conversation exposes a further difficulty: contact does not guarantee understanding, because the Trisolarans cannot comprehend a significant portion of humanity’s reference materials.

Mapping the Battlefield

As the crisis develops, the Solar System is converted into an object of exact military knowledge. Chang Weisi and Zhang Beihai study a one-to-one-trillion-scale chart whose radius reaches the middle of the Kuiper Belt. Viewed from fifty astronomical units above the ecliptic plane, the display marks the orbits of planets and satellites, records the conditions of known asteroids, and can produce a precise sectional layout for any point in the next millennium. Yet when the positional markings are switched off, the immense system becomes almost entirely dark: the Sun is a tiny yellow spot, Jupiter is barely visible, and the other seven major planets disappear.

The map’s scale produces a strategic and philosophical reversal. A system containing humanity’s entire world can be rendered as darkness surrounding a minute central star. Zhang Beihai’s observation that humanity faces major changes follows from this new military vision: the Solar System is no longer a settled cosmic neighborhood but a battle map whose bodies, distances, and trajectories must be interpreted as future positions in a war.

Humanity’s first advances are correspondingly modest. The completion of the space elevator and the breakthrough in controlled fusion encourage the world and reduce defeatist sentiment, but sober leaders compare the achievement to reaching a shore with tools while the shipyards have not yet been built. Spacecraft bodies are only one part of the task; weapons, recirculating ecosystems, and spaceports remain an unprecedented frontier, and establishing the foundations of a fleet may take a century. The Solar System imposes a material timetable that political urgency cannot simply abolish.

Planetary Defense and Technological Division

The space elevator enables large-scale exploration of the other planets, but these expeditions are practical rather than romantic. Manned landings on Mars and the moons of Jupiter are intended chiefly to establish bases for the defense of the Solar System. Strategic attention then turns inward, since the growing study of space warfare makes it increasingly difficult to ignore the value of Venus and Mercury. The PDC narrowly approves Rey Diaz’s proposal to test a Stellar Hydrogen Bomb on Mercury, marking the moment when another planet becomes a laboratory for humanity’s desperate military calculations.

The Mercury project reveals the physical resistance of the Solar System to easy engineering. Excavating a shaft through Mercury’s rock is humanity’s first large-scale construction project on another planet. Work can occur only during Mercury’s eighty-eight-Earth-day nights, so completion is expected to take three years. Even then, the shaft reaches only one-third of its projected depth before an unusually hard mixture of metal and rock makes further excavation too slow and costly. Testing at the existing depth would eject surrounding material into a crater and reduce the experiment to a weakened atmospheric test, while the crust would interfere with observation of the result.

The future fleet is shaped by an institutional dispute as much as by physics. If controlled nuclear fusion is achieved, spacecraft development divides between media-propelled vessels and non-media radiation-drive vessels. The aerospace faction favors the former, which are safer extensions of fusion-powered chemical rockets; the space force supports radiation drive because it appears to offer the only route to interstellar voyages. Media-propelled spacecraft would devote roughly two-thirds of their carrying capacity to propulsion media, consume it quickly, and require planetary bases for navigation. The competing choices therefore determine not only engineering priorities but the strategic geography of the Solar System: whether humanity remains dependent on a chain of planetary bases or seeks a more independent mode of movement.

The Trisolarans recognize the political consequences of this division. In the Three Body virtual world, Qin Shi Huang argues that nonintervention is correct because physics has been locked down by Sophon interference. Radiation-drive research, in his view, would become a nearly unsurpassable technological peak into which humanity could pour its time and resources without reaching interstellar power. The Solar System’s defense program can thus be encouraged precisely because it may trap humanity within a strategically limited technological path.

Social and Ecological Transformation

The defense of the Solar System consumes more than money and machinery. Leaders expect the space-defense system to absorb such enormous resources that the quality of life may fall back by a century. To prepare for the long war, Zhang Beihai is appointed commander of the Special Contingent of Future Reinforcements. He proposes that its officers spend at least a year training and working in space before entering hibernation, so that future political cadres will not be landlubbers when they are awakened to serve the space force. One month after the proposal is approved, he and the first contingent of thirty comrades depart for space.

The political order changes with the militarization of the Solar System. Later, Luo Ji learns that the old great powers have disappeared and that all countries have declined in political influence. The force that rises above them is a suprastate entity: the space fleet. The Solar System’s strategic demands therefore reorganize sovereignty itself. A planetary crisis that begins as an international emergency produces a new center of power whose authority derives from command of space rather than from the traditional nation-state.

The costs are environmental as well as political. As economic transition and the accelerated construction of space forces drive the growth of heavily polluting industry, environmental protection is treated as treasonous because many people believe that Earth will belong to the Trisolarans regardless. Environmental organizations are suppressed as though they were branches of the Earth-Trisolaris Organization. Greenhouse warming, climate anomalies, and desertification spread; agricultural production collapses, grain reserves are exhausted, and the Great Ravine follows. The Solar System defense effort therefore treats Earth as a resource base while helping damage the terrestrial environment it is meant to protect.

Catastrophe, Dust, and Persistence

The arrival of ten small Trisolaran probes demonstrates that humanity will encounter Trisolaran entities before the main fleet. The probes are expected to reach the Solar System roughly half a century earlier than the fleet, because they have been launched with even greater acceleration. This discovery compresses the strategic timetable again: the system is threatened not by one distant arrival but by successive waves of contact, each forcing humanity to revise its assumptions about time and preparedness.

After the annihilation of the combined human fleet, Escapism returns after two centuries of silence. The European Commonwealth proposes selecting one hundred thousand people for departure by nationwide drawing, and the plan passes a popular vote, but those not selected riot. After the Battle of Darkness among surviving warships, escape acquires an even darker meaning. The severing of spiritual bonds with Earth appears to produce total alienation, leading to the fear that a successful escape would preserve not human civilization but a hostile Negacivilization. As the droplet approaches Earth, crowds gather around spaceports and space-elevator bases to prevent any departure, armed with laser pistols that could become unstoppable when tens of thousands focus their beams on one point.

Even under this pressure, the Solar System remains a field for improvised engineering. The Snow Project proposes using Stellar Hydrogen Bombs and Neptune’s oil film to manufacture clouds of space dust that the droplets will leave tracks in as they pass. The project turns the Solar System’s planetary materials into an observational instrument: dust is not merely debris but a medium through which an otherwise nearly invisible enemy might be detected.

Five years later, the gravitational-wave antenna near northern China embodies a less destructive form of planetary engineering. The immense horizontal cylinder, one and a half kilometers long and fifty meters in diameter, hangs above the ground by antigravity. Its continuous, unmodulated emissions resemble the gravitational waves of supernovae, neutron stars, and black holes; the beam gathers water vapor, producing localized rain and creating a green meadow in the northern Chinese desert. The antenna makes the Solar System legible through a human-built signal while also altering its immediate climate. Beneath its mirrored surface, Luo Ji, Zhuang Yan, and their child encounter a structure that resembles the Sophons’ unfoldings and the droplet, a reminder that humanity’s attempts to understand the Trisolaran world inevitably reshape the world it inhabits.