Colonizing Mars

Colonizing Mars is the near-term project of putting permanent, self-sustaining human settlements on the Martian surface — distinct from the centuries-long dream of terraforming the whole planet. The terraformer asks how to make Mars Earth-like; the colonist asks something smaller and far more urgent: can a few hundred people, in pressurized habitats on a lethal world, stay alive and keep building after the ships from Earth stop coming?

The plan, in two versions

The maximalist version is Elon Musk's. SpaceX designed Starship — a fully reusable heavy-lift vehicle — explicitly to move cargo and people to Mars at a cadence and cost no prior rocket approached, with the stated long-range goal of a self-sustaining city of roughly a million people. The rationale is insurance: a second, independent home for humanity as a hedge against any single-planet catastrophe.

The frugal version came first. Engineer Robert Zubrin's Mars Direct (1990, with David Baker; expanded in his 1996 book The Case for Mars) argued that a crewed program was affordable decades ago if you stopped hauling everything from Earth. Its key move is in-situ resource utilization (ISRU): land a chemical plant ahead of the crew and run the Sabatier reaction, combining hydrogen with carbon dioxide drawn straight from Mars's thin CO2 atmosphere to manufacture methane and water — fuel for the trip home and oxygen to breathe, made on arrival rather than carried.

The environment is trying to kill you

None of this is gentle. Mars has no global magnetic field and almost no atmosphere, so the surface absorbs both galactic cosmic rays and solar storms; settlers would likely live under metres of regolith, in buried structures, or inside lava tubes for shielding. The soil is laced with perchlorates — chlorine salts that are toxic to the human thyroid and must be scrubbed from any soil used for farming or construction. And Martian gravity is 0.38g: we have decades of data on muscle and bone loss in zero-g aboard the ISS, but essentially none on what a third of Earth's gravity does to a developing fetus, a child's skeleton, or a body over a lifetime. That last unknown sits underneath every claim about permanence.

The "survive if resupply stops" test

The honest threshold for a colony — as opposed to a very remote research base — is whether it can survive being cut off. A base resupplied from Earth every 26 months (when the launch windows align) is an outpost, dependent and provisional. A colony has to manufacture its own air, water, food, energy, spare parts, and eventually the machines that make those things, using local materials, with no shipment coming. Closed-loop life support at that scale has never been demonstrated anywhere, including on Earth. It is the difference between visiting and staying, and nothing yet built clears it.

Habitats versus planets

Mars colonization is one side of a real argument about where a spacefaring civilization should actually live. The other side — associated with Gerard O'Neill and Jeff Bezos — holds that planets are a trap: deep gravity wells, fixed conditions, limited surface area. Their alternative is to skip Mars and build free-flying rotating habitats with engineered gravity and tunable climates, which could in principle house far more people than any planetary surface. The Mars camp counters that a planet supplies what an empty habitat cannot: a gravity well that catches resources, a real atmosphere, raw material underfoot, and a destination with its own meaning. The disagreement is genuine, and neither side has won it.

The ethics of contamination

There is also a quieter question. Mars may host life, or may once have, and the planetary protection norms maintained through COSPAR (the international Committee on Space Research) exist to keep Earth microbes from contaminating sites before we can study them. Crewed settlement makes strict protection effectively impossible — a human body is an ecosystem — which forces a hard trade-off between the scientific value of a pristine Mars and the ambition to inhabit it. Settling Mars may mean deciding, irreversibly, that we will never know whether it was already inhabited.

Related concepts

Colonizing and Terraforming Mars

O'Neill Colonies

Settling Space

The Great Filter

Appears in

The Shape of an Ordinary Day: Life from the Age of Agents to the Far Side of the Singularity