Sydney PhD Student Maps Martian Soils to Guide Future Mars Exploration

Daniel Irving, a PhD student at the University of Sydney, has completed the first systematic classification of Martian soils—a framework that could reshape how scientists approach future exploration and habitation on the Red Planet. The work, published in the soil science journal Catena, organizes nearly 800 million locations across Mars into a hierarchy of 2000 distinct soil classes, each mapped to specific regions of the planet's surface.

The classification system, called the Provisional Polythetic Areth Classification System (PPACS), groups Martian soils into 10 major realms, 100 assemblages, and 2000 detailed forms. The term "areth" derives from Ares, the Greek god of war and namesake of Mars. Irving and his team built the system by analyzing orbital observations and models, examining properties including texture, mineralogy, pH, and profile thickness. The resulting map covers 92 percent of the Martian surface, giving researchers a visual reference for where different soil types occur and how they relate to one another.

What makes this work significant is its scope and integration. Scientists have previously mapped Mars' geology, mineralogy, and chemistry in isolation, but Irving's system brings these properties together into a single framework. As Irving explained, this allows researchers to understand how different Martian soils connect and where they're distributed—knowledge that becomes practical when planning future missions. His supervisor, Professor Alex McBratney, noted that a future greenhouse on Mars would need more than air, water, and light; builders would need to understand what lies beneath the surface to identify the best starting points for growing plants.

The researchers tested all 2000 soil classes against characteristics important to plant production: water-holding capacity, pH, profile thickness, clay content, and gravel content. One class, Nohibareth, emerged as the most promising candidate, scoring 0.93 on a zero-to-one grading scale. Nohibareth soils have a modeled average pH of 6.8, 72 percent clay content, minimal sand or gravel, and an estimated water-holding capacity of 202 millimeters per meter. The map places these soils primarily in Mars' mid-latitudes, around Tharsis, central Arabia Terra, and Elysium Planitia, where they cover 0.14 percent of the planet's surface. However, the researchers were careful to emphasize that these areas are candidates for closer investigation, not selected greenhouse sites. Water-holding capacity emerged as the limiting factor in 73 percent of the soil forms studied, with classes in the Fareth and Mareth realms scoring below 0.3 in the assessment.

The team stressed that crops could not be grown directly in Martian soil as it exists. Future habitats would still require controlled environments, supplemental water, added nutrients, and treatment of potentially harmful substances. The next phase of research will unfold on Earth. Scientists plan to create or obtain Mars-like substrate mixtures representing the mapped classes, then test them in controlled growing spaces with actual crops, added nutrients, and managed water. These experiments could reveal how plants respond to each mixture, how much water they require, and what treatment would be necessary to make each substrate safe for cultivation.

Over time, rover measurements and samples collected directly from Mars could verify whether the promising mapped classes are actually present where the models predict them. The current map does not account for factors such as perchlorate toxicity or nitrogen availability, and many input properties are inferred from orbital data and terrestrial relationships rather than direct measurement. As new data arrives from Mars missions, the classification system will need revision and refinement.

The research may also offer insights for Earth scientists studying some of the planet's most challenging landscapes—the Atacama Desert, the Pilbara region, and various polar zones. McBratney noted that while people often assume soil requires substantial organic matter to function, certain Earth soils, particularly in arid regions, contain very little organic matter. The Martian research, paradoxically, may help scientists think more deeply about how such soils work and what might be done with them. Irving concluded that as rover missions continue to collect data about Mars, scientists need consistent frameworks to organize and compare that knowledge. This classification system provides that framework, one designed to grow and evolve as new information becomes available.