IISc and ISRO Create Sustainable Space Bricks from Martian Soil for Mars Colonization

Imagine standing on Mars, looking out over a small colony of dome-shaped homes—not made from concrete or metal, but from the very soil beneath your boots. Sounds like science fiction? Thanks to an incredible breakthrough from India, it’s inching closer to reality.

A research team from the Indian Institute of Science (IISc), in collaboration with ISRO, has developed an innovative way to make “space bricks” using Martian soil and a little help from microbes. Their goal? To build sustainable structures on Mars without relying on expensive shipments from Earth.

The secret lies in a clever natural process called Microbial-Induced Calcite Precipitation (MICP). The scientists used a special bacterium—Sporosarcina pasteurii—that can produce calcite, a binding material, when fed with urea and a bit of natural polymer. Mix that with Martian soil simulant, and voilà—you get strong, compact bricks, ready for construction.

What’s really fascinating is that this method doesn’t need heavy machinery or cement. The research used a Mars Soil Simulant (MSS) to test how well the bricks form, and trials were conducted in a specially designed MARS chamber—a setup that mimics Mars-like conditions. They even used lab-on-chip technology to monitor how the bacteria worked in extreme environments.

Why does this matter? Because for future human missions to Mars, bringing materials from Earth is not practical. The answer lies in In-Situ Resource Utilization (ISRU)—basically, using what’s already available on Mars to survive and build. These microbial space bricks fit perfectly into that vision.

In short, Indian scientists are showing us a future where our homes on Mars could be literally grown, not built—paving the way for greener, smarter, and more efficient extraterrestrial living.

Background and Objectives

Mars missions (by NASA, ESA, ISRO and others) recognize ISRU – using local materials – as key for sustainable habitats . Martian regolith is abundant but hostile; transporting Earth-made bricks is costly. The IISc–ISRO team’s solution: convert Mars “soil” into bricks using microbes. In their April 2022 PLOS ONE study, Dikshit et al. demonstrated that a slurry of Martian soil simulant, Sporosarcina Pasteurii, urea, nickel chloride, and guar gum consolidates into solid bricks over days . These space bricks could be molded into habitats on-site with an eco-friendly, low-energy process – essentially using bacterial “cement” instead of Portland cement.

Their goals included:

• Demonstrate feasibility of microbial cementation for Martian soil.
• Optimize materials (soil simulant, additives, microbes) for strength and density.
• Overcome Martian soil hazards (iron toxicity, salts).
• Test structures in Mars-like conditions (CO₂ atmosphere, low gravity).
• Assess ISRU implications for space colonization.

Materials

In their innovative approach to Martian construction, the IISc–ISRO team carefully selected and optimized materials for the Microbial-Induced Calcite Precipitation (MICP) process. The goal was to transform Martian soil simulant (MSS) into durable construction bricks using a microbial-based method. The components of the slurry are as follows:

• Martian Soil Simulant (MSS): The primary substrate for the biocementation process, MSS is a Mars-analog regolith sourced from the Class Exolith Lab (Florida). This soil simulant is chemically and physically analogous to Martian dust, with a composition that is iron-rich and fine-grained, closely resembling the real Martian soil found on the planet’s surface. The MSS serves as the primary building material, providing the necessary mineral base for the formation of calcium carbonate (CaCO₃) under microbial activity.
• Sporosarcina pasteurii (Urease-Producing Bacterium): Sporosarcina pasteurii is a urease-producing bacterium used to catalyze the hydrolysis of urea, resulting in the precipitation of calcium carbonate. The urease enzyme, secreted by the bacterium, facilitates the conversion of urea into ammonia and carbonate ions, which react with calcium present in the soil simulant to form CaCO₃. This process is central to the microbial cementation technique, acting as a natural binding agent to consolidate the soil particles into a rigid structure.
• Urea: A key reactant in the biocementation process, urea serves as a nitrogenous compound that provides carbonate ions essential for calcium carbonate formation. Urea is typically found in biological waste, including human urine, and in this study, it is utilized not only as a chemical feedstock but also as an example of a potential closed-loop resource for space missions. The use of urea in the Martian context underscores the feasibility of resource recycling and self-sufficiency in extraterrestrial habitats.
• Nickel Chloride (NiCl₂): The inclusion of Nickel Chloride in the slurry provides essential Ni²⁺ ions, which act as a cofactor for the urease enzyme. Nickel is crucial to activating the urease pathway, promoting the efficient conversion of urea into the necessary carbonate ions that drive the formation of calcium carbonate crystals. Without the presence of nickel, the urease enzyme would not function optimally, thereby hindering the cementation process.
• Guar Gum: A natural polymer derived from guar beans, guar gum serves as a thickening agent in the slurry, improving the rheological properties of the mixture. Its inclusion in the slurry also enhances the mechanical strength of the final bricks. Even in small quantities (approximately 1% by weight), guar gum significantly improves the cohesion and overall durability of the cemented structure, making the resulting bricks more resilient and capable of withstanding the harsh Martian environment.

The combination of these components creates a slurry that is poured into molds to form the desired brick shapes. After inoculating the slurry with Sporosarcina pasteurii, the mixture undergoes an incubation period during which the bacteria produce calcium carbonate, cementing the soil particles into a solid structure. The typical molds used in the IISc laboratory experiments were 1-2 inches in size, but the method is scalable to accommodate various sizes and shapes, making it adaptable for large-scale construction in future Martian habitats.

Methodology

The Microbial-Induced Calcite Precipitation (MICP) process is the cornerstone of the IISc–ISRO team’s approach to creating sustainable construction bricks on Mars. The core principle involves harnessing bacteria to convert urea into calcium carbonate (CaCO₃) crystals, which act as a binding agent for the Martian soil simulant (MSS). Here’s a detailed breakdown of the process:

Microbial Metabolism:

The process begins with the bacterium Sporosarcina pasteurii, which produces the enzyme urease. This enzyme catalyzes the hydrolysis of urea, leading to the release of ammonium (NH₄⁺) and carbonate ions (CO₃²⁻). The reaction can be described as follows:

CO(NH₂)₂ + 2H₂O→2NH₄⁺ + CO₃²⁻

The carbonate ions (CO₃²⁻) then combine with calcium ions (Ca²⁺) from the Martian soil simulant or added salts to precipitate calcium carbonate (CaCO₃). The CaCO₃ is primarily formed in the calcite or aragonite crystal forms. The process also raises the pH, which further promotes the formation of calcium carbonate crystals. These crystals, along with biofilms produced by the bacteria, fill the pore spaces within the soil, effectively “cementing” the soil particles together into a solid structure.

The precipitation of calcium carbonate not only binds the particles but also enhances the overall strength of the material, forming a durable, brick-like substance. As described, the bacteria convert the urea into CaCO₃ crystals, which, in combination with the biopolymers secreted by the microbes, bind the soil particles to form a cohesive material.

Slurry Casting Process:

To ensure repeatability and scalability, the IISc–ISRO team developed a slurry casting method, which involves several key steps:

1. Bacterial Culture:
   • Sporosarcina pasteurii is cultured in a synthetic broth containing urea and trace amounts of nickel chloride (NiCl₂). The Ni²⁺ ions from NiCl₂ are essential for activating the urease enzyme, enhancing the bacterial activity in the process. The culture is grown until it reaches an optical density (OD) of approximately 0.8.
2. Prepare Slurry:
   • The Martian Soil Simulant (MSS) is mixed with 1% guar gum (w/v), filter-sterilized urea, and 10 mM NiCl₂. The guar gum acts as a thickening agent, improving the consistency of the slurry and adding to the strength of the final product. The S. pasteurii inoculum is added to the mixture, creating a homogeneous slurry.
3. Casting:
   • The prepared slurry is poured into molds of various shapes, including cubes, cylinders, and hollow forms. The casting process is highly versatile, allowing the team to create complex shapes for potential Martian habitats and infrastructure.
4. Curing:
   • The molds are incubated at approximately 30°C for 15 to 20 days. During this incubation period, the bacteria actively precipitate calcium carbonate, which binds the soil particles and gradually strengthens the structure. Over time, the soil simulant undergoes a transformation, slowly turning into a solid brick-like form. The final drying process ensures that excess water is removed, solidifying the material further.

Testing and Equipment:

• The casting process and the final products are tested for strength using standard laboratory equipment. The samples are compression-tested on an Instron machine at a rate of 1 mm/min to assess the structural integrity of the bricks.
• To characterize the microstructure and mineralogy of the material, techniques such as Field Emission Scanning Electron Microscopy (FESEM) and X-ray Diffraction (XRD) are employed. These methods help to examine the crystal formation, material composition, and the overall durability of the biocemented bricks.

This methodology demonstrates a highly sustainable and low-energy approach to producing construction materials using locally available resources on Mars. The innovative use of microbial cementation not only offers a promising solution for In-Situ Resource Utilization (ISRU) on Mars but also highlights the potential for closed-loop systems that reduce the need for Earth-supplied materials in space missions.

Challenges and Solutions

Martian Soil Hazards:

One of the first challenges the team encountered was the toxicity of Martian soil to Earth microbes. The Martian Soil Simulant (MSS) used in their experiments contained approximately 6.9% iron by weight, primarily in the form of ferric oxide. Iron ions can act as a poison to Sporosarcina pasteurii, inhibiting its growth and the production of urease, an enzyme essential for the microbial cementation process. Early trials revealed that the bacteria failed to grow at all in plain MSS.

To overcome this, the team introduced nickel chloride (NiCl₂) into the mixture. Nickel ions (Ni²⁺) are crucial for activating the urease enzyme, effectively “kick-starting” the bacterial metabolism. With the addition of 10 mM NiCl₂ and 1% guar gum, the team was able to significantly improve the strength of the resulting bricks, achieving a compressive strength of approximately 3.3 MPa—roughly double the strength of bricks made without nickel.

Chemical Inhibitors:

Another significant challenge is the presence of perchlorates, sulfates, and other chaotropic salts in Mars’ soil. These compounds have been shown in previous studies to inhibit or prevent microbial metabolism. Given their potential to interfere with the microbial cementation process, the team initially worked with a simulant that was free of added perchlorates.

The IISc–ISRO team acknowledges the need to address this issue in future work. They plan to test Martian regolith simulants containing perchlorates and may incorporate perchlorate-reducing microbes into the system to mitigate any inhibitory effects. This adaptation will be crucial for ensuring that microbial cementation remains viable in the presence of these potentially harmful chemicals.

Thin CO₂ Atmosphere:

Mars’ thin atmosphere, which is composed of approximately 95% carbon dioxide (CO₂) and has a pressure of around 0.6% of Earth’s atmospheric pressure, presents another challenge. Such conditions may impact bacterial growth and the curing process of the microbial cement. To simulate these conditions, the IISc–ISRO team developed the MARS (Martian AtmospheRe Simulator)—a controlled chamber designed to replicate the atmospheric pressure and composition of Mars.

This MARS simulator allows the team to test how space bricks cure under Martian-like conditions, with a CO₂ pressure of 7 mbar. By understanding how the microbial cementation process behaves in a Martian environment, the team can optimize the process for future Mars missions.

Low Gravity:

Microgravity, which would be encountered on Mars or during space travel, presents another unknown factor that could influence the fluid flow, bacterial settling, and microbial metabolism during the cementation process. To better understand these effects, the team is developing a lab-on-chip device that can monitor the activity of Sporosarcina pasteurii in microgravity conditions.

These devices, which may be tested on India’s Gaganyaan mission, will help the team assess whether space bricks can be produced during space travel or in low-gravity environments. This research is essential for determining the feasibility of using microbial cementation in a variety of space habitats, whether on the Moon, Mars, or in interplanetary transit.

Results and Performance

The team’s experimentation with Microbial-Induced Calcite Precipitation (MICP) for creating Martian bricks yielded promising results in terms of both compressive strength and microstructural integrity.

Compressive Strength:

The bricks produced with 1% guar gum and 10 mM nickel chloride (NiCl₂) demonstrated a compressive strength of approximately 3.3 MPa when made with Martian Soil Simulant (MSS). This strength is about 10–15% of typical Earth concrete, which, although lower than Earth standards, is deemed adequate for building certain structures on Mars. As a point of comparison, bricks made from lunar simulant under similar conditions achieved a higher compressive strength of approximately 5.6 MPa.

• 1% guar gum alone yielded 1.1 MPa, while 10 mM NiCl₂ alone produced 2.7 MPa.
• The combination of both additives demonstrated synergistic effects, significantly enhancing the strength.
• However, increasing concentrations of NiCl₂ or guar gum beyond these levels led to diminishing returns, suggesting that these concentrations are optimal for maximizing strength without wasting resources.

Porosity Reduction:

The MICP process also showed notable reductions in porosity, as the bacteria and their biopolymers penetrated the pore spaces between the soil grains, binding them tightly. This result was reflected in the strengthening of the bricks due to the decreased void spaces.

• One report observed that “bacteria seep deep into the pore spaces,” effectively decreasing porosity and contributing to stronger bricks.
• The SEM images of the bricks confirmed that CaCO₃ crystals bridged the particles, solidifying the structure, while X-ray micro-CT (not included in the study) would likely show a dense microstructure.

Microstructure (SEM/XRD Analysis):

The SEM images revealed the presence of crystalline precipitates of calcium carbonate (CaCO₃) coating the Martian soil grains. The X-ray diffraction (XRD) analysis of the optimal brick composition, containing MSS, S. pasteurii, NiCl₂, and guar gum, showed distinct peaks for calcite (e.g., at 29.2° and 35.5° 2θ), with minor peaks for aragonite and vaterite phases.

• Control samples (without any additives) showed almost no CaCO₃ peaks, confirming that microbial treatment was responsible for generating the cementing minerals.
• Thermogravimetric analysis indicated that approximately 3% of the brick composition was CaCO₃, further validating the biomineralization process.

Durability:

In laboratory tests on Earth, the bricks showed promising durability. They remained intact under handling and modest loads, demonstrating sufficient strength for practical applications. Furthermore, the team applied the MICP slurry to repair cracks in high-strength sintered bricks designed for lunar applications. The repaired bricks successfully restored much of the lost strength, and were able to withstand temperatures ranging from 100°C to 175°C without failure. This suggests good thermal stability, which is particularly promising given the extreme day-night temperature variations on Mars.

• While Mars-specific tests have not yet been conducted under Martian conditions (e.g., in a Mars chamber), the researchers expect the results to be similar due to the robustness of the method.

Mars Condition Simulation:

To simulate Martian environmental conditions, the team has initiated trials using the MARS (Martian Atmosphere Simulator) chamber. These trials are designed to cure bricks under conditions of low-pressure CO₂—a condition similar to what would be encountered on Mars.

• Preliminary tests will evaluate whether the bacteria remain active in low-pressure CO₂ environments and whether CaCO₃ precipitation can occur as effectively as under Earth-like conditions.
• Additionally, microgravity experiments are being planned to assess how the bacteria and cementation process behave in space. The results of these experiments will determine whether space bricks can be produced during space missions or under low-gravity conditions, with viability and cementation rate being key focus areas.

Production Rate:

The casting process used to create the bricks is highly scalable, allowing for the production of multiple molds in parallel. This is a significant advantage over previous methods, such as those used for lunar brick production, which relied on packing techniques. With casting, the team can also produce hollow or interlocking shapes, which may be more suitable for designing complex structures.

• The ability to produce multiple bricks simultaneously, as well as to customize shapes, makes this method a scalable solution for Martian construction, paving the way for potential large-scale production in future space missions.

Discussion and Implications

The IISc–ISRO Mars brick project represents a groundbreaking development in extraterrestrial civil engineering, offering a potential solution for building habitats on Mars using local materials and Earth microbes. The research demonstrates a low-energy, sustainable approach that could revolutionize the way we think about construction beyond Earth.

In-Situ Resource Utilization (ISRU):

One of the key innovations of this research is the use of Martian regolith, or Mars soil, as a building material. This aligns with the ISRU strategy that NASA has emphasized, which focuses on using local resources for building structures and other necessities on Mars. By harnessing microbial cementation, the process effectively transforms Martian dust into strong, durable bricks. This method significantly reduces reliance on Earth-based supplies, which is crucial for long-term missions. As NASA notes, “the farther humans go… the more important it will be to generate products with local materials.” This project exemplifies how waste products (like urea) can be converted into valuable building assets, contributing to sustainable space exploration.

Self-Sufficiency:

This method’s potential to reduce supply needs is another major advantage. By utilizing urine (urea) as a feedstock, the process minimizes reliance on external resources for construction materials. Additionally, the robust bacterium used in the process can thrive in Martian conditions and self-heal structures over time. The low-energy curing process, which does not require high-temperature sintering, is particularly advantageous for remote colonies where energy resources will be scarce. Furthermore, guar gum—a key additive—can be transported as seeds or bioreactors to Mars, eliminating the need for complex supply chains for every component.

Versatility and Repair:

Beyond initial construction, this microbial cementation process offers long-term benefits through its self-healing properties. As demonstrated in recent experiments, the bacterial cementation can be used to repair cracks in existing structures, ensuring that habitats and other infrastructure can be rejuvenated and maintained in-situ, without needing to ship materials from Earth. This self-repairing capability greatly enhances the longevity of structures on Mars, making them more resilient to wear and environmental stressors like temperature fluctuations, dust storms, and radiation.

Integration with Other Technologies:

These bio-bricks could complement other technologies used in Martian construction. For example, 3D printing could be employed to create a basic framework for habitats, while bio-cemented bricks could be used to fill in the structure. Additionally, waste CO₂ from life support systems could potentially be used to carbonate the bricks, mimicking terrestrial CO₂ sequestration methods. This kind of integration could lead to modular, adaptable, and scalable solutions for building structures on Mars, allowing for more efficient use of resources.

Extraterrestrial Civil Engineering Field:

This project underscores the interdisciplinary nature of constructing habitats off Earth. It brings together civil engineers, microbiologists, and space scientists—a collaboration essential for tackling the complex challenges of building on Mars. Terminologies like “space bricks” and “microbial cementation” are entering the lexicon, reflecting this fusion of disciplines and highlighting the innovative approaches being developed for extraterrestrial construction.

Future Steps:

To advance this technology further, the team plans long-term testing under Martian conditions, including testing brick strength in a Mars chamber and assessing durability under extreme conditions such as freeze-thaw cycles and radiation exposure. The team also plans to scale up production with pilot-scale trials to determine the most effective mixing and curing techniques. Additionally, sensors integrated into the lab-on-chip devices and the use of autonomous robots for mixing and curing could streamline the process, allowing it to become a practical, scalable technology. Over time, this data will help establish design standards for brick strength, binder ratios, and other factors critical for mission planners and engineers working on Mars.