Building a city on Mars has long been a symbol of human ambition, but the practical reality behind it is much more complex than the dream suggests. A recent preprint study by Serena Soriano explores one of the biggest hidden challenges: where building materials will actually come from.
Mars has iron, but lacks many specialized elements needed for advanced manufacturing, such as boron and molybdenum. Without these elements, building a solid infrastructure becomes extremely difficult. Because of this limitation, researchers are increasingly looking beyond Mars itself and turning their attention to main belt asteroids as a potential source of supplies.
Why does Mars appear rich in resources but in reality it is not?
Mars often appears resource-rich when viewed from a distance, but its geological history tells a different story.
Unlike Earth, it has not experienced long-term tectonic activity capable of concentrating valuable minerals into accessible deposits. As a result, most of its minerals are widely dispersed rather than available in concentrated ore veins.Iron is abundant and gives the planet its distinctive red appearance. However, iron alone is not enough to build an effective industrial base. Advanced construction requires a set of alloying elements that are either rare or extremely difficult to extract on Mars.
Experts point out that while early settlements may have relied on local resources for basic survival, large-scale development would quickly face material shortages.This creates a fundamental bottleneck. A Mars colony may be able to sustain life, but not necessarily expand into a fully developed city without importing materials from elsewhere, according to the study published at Cornell University, titled “Asteroid Mining to Sustain a Mars Colony: A Logistical Perspective.”
How the asteroid belt could become a resource center for Mars missions
To address this gap, the study proposes a bold idea: using main belt asteroids as a source of industrial materials. These asteroids, located between Mars and Jupiter, contain bodies rich in metals and volatiles. Metallic asteroids can provide iron and nickel, while carbon-rich asteroids contain water and compounds that can be used to produce fuel.At first glance, this approach seems effective. In practice, it depends heavily on orbital mechanics, making the process much more complex than simply flying to a nearby space rock and returning with the payload.
Each flight requires precise alignment of planetary positions, fuel availability, and spacecraft capabilities.Researchers have reportedly identified a small number of asteroid pairs that could operate within realistic energy limits. However, the system will operate over very long time periods, with each supply cycle taking years rather than months.
How a Starship-like spacecraft could handle asteroid mining missions
The study designs its logistics around a spacecraft similar in capability to SpaceX’s Starship.
This theoretical vehicle has a large payload capacity but is still limited by missile laws. Much of their mass is devoted to fuel rather than charging, a limitation driven by the well-known rocket equation.Such a spacecraft, fully fueled, could achieve a delta speed of about 6.4 km/s. This is important, but not enough to complete the entire mining and return mission in one trip through the asteroid belt. Most livable roads require much more energy, often beyond what a single fuel load can support.For this reason, the study suggests a multiple stop regimen. The spacecraft will first travel to a metallic asteroid to collect materials. It will then move to a second asteroid rich in water and hydrocarbons, where it can refuel by producing propellants in space. Only after this second station will it return with its payload to Mars orbit.
The slow reality of fuel production in space
One of the most challenging aspects of this system is in situ propellant production, or ISPP.
This process involves extracting water from asteroids and turning it into usable fuel. Although this concept is well understood, the practical production rate is very slow. Some estimates indicate production rates that do not exceed a few kilograms per day under current assumptions. At this speed, it could take many years to fuel a large spacecraft.
In extreme cases, complete refueling cycles can extend into centuries if no improvements are made.This creates a major bottleneck in the system. Even if spacecraft and asteroid trajectories were viable, the refueling process alone could dominate mission timelines.
Why asteroid mining may take decades, not years
Despite the difficulties, the study does not reject the idea. Instead, it positions asteroid mining as physically possible but severely constrained by time, energy, and current technology levels. Over a long enough period of time, a single continuously operating spacecraft could deliver large amounts of material to Mars, perhaps about a few hundred tons over decades.There is also the possibility that future propulsion systems, such as solar electric motors or solar sails, will improve efficiency and reduce travel times. However, experts warn that these technologies are still evolving and may not be ready for large-scale interplanetary logistics in the near future.Ultimately, the vision that emerges is not one of rapid expansion, but one of slow accumulation. A Martian city, if it becomes a reality, might depend less on grandiose achievements and more on steady, patient supply chains stretching across the solar system.