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Overview

Mars is the fourth planet from the Sun and the homeworld of the Martian Congressional Republic (MCR), one of the three major powers in the solar system. With a population of roughly four billion people, Mars stands as the second most powerful political entity after Earth's United Nations. The planet is defined by two overriding priorities: its centuries-long terraforming project and its technologically superior military. In The Expanse: Osiris Reborn, Mars is a visitable location described by the developers as featuring "imperious political bastions" that reflect the planet's militaristic governance and its population's collective dedication to the terraforming dream.

Players who chose the Martian origin during character creation will feel a sense of homecoming when visiting Mars. Earthers and Belters, by contrast, encounter varying degrees of suspicion from the local population. The MCRN maintains a heavy presence throughout the areas the player can visit, and the contrast between Mars's ambitious vision of a green, habitable future and the current reality of a barren, domed world is a recurring theme.

Key Facts

The Martian Congressional Republic

The Martian Congressional Republic (MCR) is the sovereign government of Mars and all its settlements. It operates as a unitary parliamentary republic led by the Prime Minister, who is elected by and accountable to the Martian Congress. The Prime Minister also serves as commander-in-chief of both the MCRN and the Martian Marine Corps (MMC). While the MCR is nominally democratic, the military wields enormous political influence, and Martian society has a strongly authoritarian streak beneath its republican institutions.

The MCR is one of the two human superpowers, locked in a rivalry with the United Nations that governs Earth and Luna. Despite having a significantly smaller population than Earth, Mars has carved out strategic parity through technological superiority and the discipline of its people. The ruggedness that comes from surviving on a hostile world with sparse resources has produced a population that views itself as tougher and more purposeful than Earth's.

Government buildings are concentrated in Aterpol, the downtown district of Londres Nova. The capital also houses a major university with campuses in Breach Candy (one of the oldest complexes on the planet) and Salton.

The Terraforming Project

The Mars Terraforming Project is widely considered the greatest engineering undertaking in human history. Its goal is to transform Mars from a barren, radiation-blasted desert into a world with a breathable atmosphere, liquid water, and a self-sustaining biosphere. The project has been running for generations, involving most of the population either directly or indirectly. Tall terraformer towers dot the Martian surface, slowly processing the atmosphere and warming the planet.

Terraforming is not just an engineering project; it is the cultural and spiritual heart of Martian identity. Every Martian grows up understanding that they are working toward a future they themselves will never see. The dream of standing on Mars under an open sky, breathing real air, is passed down from parent to child. This generational sacrifice gives Martian society a sense of shared purpose that Earth, with its billions of unemployed citizens, lacks entirely.

The project also shapes Martian politics. Resources that could go toward improving daily life are instead funneled into the centuries-long effort. This tension is a source of internal debate, and younger generations of Martians have begun questioning whether the dream is worth the cost, particularly as they grow accustomed to life in domed settlements. In the game's timeline, the terraforming project remains an active and defining element of Martian civilization.

Cities and Infrastructure

Martian cities are built partly underground and partly within pressurized surface domes. The capital, Londres Nova, is located in the northern reach of the Aurorae Sinus region. Its layout consists of a webwork of tunnels carved under the Martian permafrost over generations, using the soil as insulation and radiation shielding in the absence of a planetary magnetosphere. Ten domes press out to the surface, with Salton located beneath the largest agricultural dome. Seven neighborhoods radiate outward below the surface.

An advanced mass transit network connects the city's districts, including cable cars that span canyons and underground metro systems. Residential areas feature modern amenities comparable to Earth cities, though adapted for Martian conditions. The living standards are generally high, reflecting a society that invests heavily in infrastructure and education rather than consumer luxury.

Other significant settlements exist across the planet, connected by surface transport and subterranean corridors. Military installations, research complexes, and terraforming facilities are scattered across the Martian surface. The distinction between civilian and military infrastructure is often blurred, as Mars's entire society is oriented toward collective goals.

MCRN Military

The Martian Congressional Republic Navy (MCRN) is the most important branch of Mars's military and the primary instrument of Martian power projection. Although smaller in total ship count than the United Nations Navy (UNN), the MCRN is more technologically advanced and is generally considered to be on par with or superior to its Earth counterpart in combat effectiveness.

The MCRN is organized into two major fleets. The Home Fleet is stationed at Mars, responsible for planetary defense and the security of Martian orbital assets. The Jupiter Fleet operates between Ceres and Ganymede, projecting Martian power into the Belt and the Jovian system. This forward deployment ensures that Mars can respond to threats across a vast stretch of the solar system.

Notable Ship Classes

Mars also fields the Martian Marine Corps (MMC), an elite ground and boarding force. Martian Marines are equipped with advanced power armor and are trained for operations in zero gravity, low gravity, and standard gravity environments. The combination of naval superiority and ground force capability makes the MCRN a formidable opponent for any faction in the solar system.

Martian Culture

Martian culture is defined by military discipline, engineering excellence, and a collective dedication to the terraforming project. All Martians are required to serve in the military beginning at age 18, and this compulsory service shapes the population's values from an early age. Duty, sacrifice, and loyalty to Mars are drilled into every citizen.

Unlike Earth, where billions live on Basic Assistance with no clear purpose, every Martian has a role. Engineers, scientists, soldiers, and farmers all contribute to the shared project of making Mars habitable. This sense of purpose creates a fiercely nationalistic population that looks down on what it sees as Earth's complacency and the Belt's lawlessness.

Education is highly valued. Londres Nova's university system is one of the oldest on Mars and produces the engineers and scientists who drive the terraforming effort. Martian technological innovation consistently outpaces Earth's, particularly in military applications, propulsion systems, and atmospheric processing.

The official Twitter/X account for The Expanse: Osiris Reborn highlighted this duality in Martian life: "Some Martians dedicate their lives to terraforming the red planet. Others join the Navy and train hard to protect the efforts of the former." This captures the two pillars of Martian society: the dream of a green Mars and the military strength required to protect it.

Role in The Expanse: Osiris Reborn

In The Expanse: Osiris Reborn, Mars is one of the major visitable locations alongside Eros Station, Ceres Station, Ganymede, and Lovell City on Luna. The Steam store description places Mars among "the imperious political bastions" that players will explore, positioning it as a location focused on political intrigue and military authority rather than the seedier commerce of Belt stations.

Mars functions as a social hub between missions. Players can interact with MCRN officials, explore military facilities and terraforming infrastructure, shop for equipment, and navigate the political dynamics of a society organized around collective discipline. The areas accessible to the player reflect the planet's authoritarian character: clean, orderly, and heavily patrolled.

Players who selected the Martian origin during character creation will experience unique dialogue options and NPC reactions on Mars. As a returning Martian, the player receives a more welcoming reception and may gain access to side content tied to their homeworld. Earthers and Belters face greater scrutiny and hostility from the local population, which mirrors the faction-based social dynamics seen on Ceres Station and other hubs.

The game's choices and consequences system tracks the player's relationship with Martian characters and institutions. Decisions made on Mars can shift the player's standing with the MCRN and influence how the broader political conflict between Earth, Mars, and the Belt plays out in the narrative.

Political Significance

Mars occupies a unique position in the solar system's political landscape. It is neither the oldest power (Earth holds that distinction) nor the most numerous (the Belt's scattered population is comparable in total), but it is arguably the most focused. Every aspect of Martian society, from education to economics to military spending, is directed toward two goals: completing the terraforming project and maintaining strategic independence from Earth.

The rivalry between Mars and Earth is the defining geopolitical axis of The Expanse setting. Earth views Mars as an upstart colony that grew too powerful; Mars views Earth as a bloated, decadent civilization resting on the laurels of having been born first. This mutual contempt drives an arms race that has produced some of the most advanced military technology in human history.

Both powers look down on the Belt and its inhabitants. Mars sees Belters as undisciplined and scattered, lacking the shared purpose that holds Martian society together. The OPA (Outer Planets Alliance) represents a growing threat to the inner-planet status quo, and Mars's response to Belt activism is shaped by the same military pragmatism that defines everything else about the planet.

In the context of the game's story, Mars is a major player in the conspiracy surrounding the protomolecule. The MCRN's interest in the alien technology, Protogen's connections to inner-planet power structures, and the fragile alliances between Earth, Mars, and the Belt all converge as the player uncovers the truth behind the events on Eros.