Building cities on Mars has long been a symbol of human ambition, but the reality behind it is far more complex than the dream suggests. A recent preprint study led by Serena Suriano explores one of the biggest hidden challenges: the actual sources of building materials. Mars does contain iron, but it lacks many of the specialized elements needed for advanced manufacturing, such as boron and molybdenum. Without these, building durable infrastructure will be extremely difficult. Because of this limitation, researchers are increasingly looking beyond Mars itself and turning their attention to main-belt asteroids as possible sources of supply.

Why Mars looks rich in resources but isn’t

From a distance, Mars often appears rich in resources, but its geological history tells a different story. Unlike Earth, it does not experience long-term tectonic activity that could concentrate valuable minerals into mineable deposits. As a result, most of its metals are widely dispersed rather than concentrated in veins.Iron is abundant and gives the earth its unique red appearance. However, iron alone is not enough to build a functioning industrial base. Advanced construction requires a range of alloying elements that are either scarce or extremely difficult to extract on Mars. While early settlements may have relied on local resources for basic survival, large-scale development quickly ran into material shortages, experts say.This creates a fundamental bottleneck. According to a study published by Cornell University titled “Asteroid Mining to Sustain a Mars Colony: A Logistics 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. Located between Mars and Jupiter, these asteroids contain metals and volatile-rich objects. 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 to work. In reality, it depends heavily on orbital mechanics, making the process much more complex than simply flying to a nearby space rock and returning with cargo. Each journey requires careful adjustments to planetary position, fuel availability and spacecraft capabilities.Researchers have reportedly discovered a handful of asteroid pairs that can work within practical energy limits. Even so, the system will still operate over a long period of time, with each supply cycle taking years rather than months.

How a Starship-like spacecraft could handle asteroid mining missions

The study models the logistics of a spacecraft with capabilities similar to SpaceX’s Starship. This theoretical vehicle would have a large payload capacity, but would still be limited by the laws of rocketry. Most of its mass is devoted to fuel rather than cargo, a limitation driven by the well-known rocket equation.With sufficient fuel, such a spacecraft can reach a delta-v speed of about 6.4 km/s. That’s significant, but not enough to accomplish a complete mining and return mission in a single trip through the asteroid belt. Most feasible routes require considerable energy, often beyond what a single fuel load can support.Therefore, the study recommends a multi-station system. The spacecraft will first travel to a metallic asteroid to collect materials. It will then travel to a second asteroid rich in water and hydrocarbons, where it can refuel by producing propellant in space. Only after its second stop will it return to Mars orbit with its cargo.

The slow reality of producing fuel in space

One of the most challenging aspects of the system is in-situ propellant production (ISPP). The process involves extracting water from asteroids and converting it into usable fuel. While the concept is easy to understand, actual production is extremely slow. Some estimates suggest that production would be only a few kilograms per day under current assumptions. At this rate, refueling a large spacecraft could take many years. In extreme cases, without improvements, a complete refueling cycle could last for centuries.This creates a major bottleneck in the system. Even if a spacecraft and asteroid route were feasible, the refueling process alone would likely dominate the mission schedule.

Why asteroid mining may take decades, not years

Despite the difficulties, the study does not dismiss the idea. Instead, it contends that asteroid mining is physically feasible but severely limited 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 in the hundreds of tons over a few decades.Future propulsion systems, such as solar electric engines or solar sails, also have the potential to increase efficiency and reduce travel times. However, experts warn that these technologies are still under development and may not be used for large-scale interstellar logistics in the near future.The vision that emerged was not one of rapid expansion but of slow accumulation. Martian cities, if they become a reality, may rely less on giant breakthroughs and more on stable, patient supply chains spanning the solar system.