Sydney researcher creates first comprehensive map of Martian soils

Daniel Irving, a PhD student at the University of Sydney, has completed the first systematic classification of Martian soils—a framework that organizes nearly 800 million locations across the Red Planet into a coherent structure that scientists can use to compare landscapes, plan exploration routes, and eventually identify where humans might grow food.

The work, published in the soil science journal Catena, introduces a new vocabulary for talking about Martian earth. Irving and his team call these soil types "areths," borrowing from Ares, the Greek god of war and namesake of Mars. The Provisional Polythetic Areth Classification System, or PPACS, arranges Martian soils into a hierarchy: 10 major realms at the broadest level, 100 assemblages in the middle tier, and 2000 distinct forms at the most detailed scale. Each classification rests on measurable properties—texture, mineralogy, pH, and the thickness of soil layers—derived from orbital observations and computational models. A global map accompanies the system, covering 92 percent of the Martian surface and showing where each soil class occurs.

"This is the first time a classification system of this scale has been developed for Martian soils," Irving said. Scientists have previously mapped Mars' geology, its mineral composition, and its chemical makeup, but this work stitches those separate threads into a single framework, allowing researchers to see how different Martian soils relate to one another and where they cluster geographically. The practical payoff is immediate: if humans ever establish a greenhouse on Mars, they will need to know what lies beneath the glass. As Irving's supervisor, Professor Alex McBratney, noted, builders would need more than air, water, and light—they would need to understand the ground itself as a starting point for growing plants.

To test whether the classification system could identify promising candidates for agriculture, the researchers evaluated all 2000 soil forms against criteria that matter for plant production: water-holding capacity, pH level, soil thickness, clay content, and gravel content. One soil class, designated Nohibareth, emerged as the strongest prospect, scoring 0.93 on a scale from zero to one. Nohibareth soils have a modeled average pH of 6.8, contain 72 percent clay, include minimal sand or gravel, and hold an estimated 202 millimeters of water per meter of depth. The map places these soils primarily in Mars' mid-latitudes, particularly around Tharsis, central Arabia Terra, and Elysium Planitia. Nohibareth soils cover only 0.14 percent of the Martian surface, but they represent the most favorable combination of properties the analysis found. Water-holding capacity proved to be the limiting factor for 73 percent of all soil forms studied; soils in the Fareth and Mareth realms all scored below 0.3, reflecting less advantageous combinations of the measured properties.

The researchers are careful to note that this does not mean crops could be planted directly into Martian soil. Any future habitat would still require controlled environments, added water, supplemental nutrients, and treatment to neutralize potentially toxic substances. The next phase of work must happen on Earth. Scientists can create or obtain Mars-like soil mixtures that match the mapped classes, then test them in controlled growing chambers with actual crops, added nutrients, and managed water supplies. Those experiments would reveal how plants actually perform in each mixture, how much water they consume, and what treatment would be necessary to make each one safe for cultivation. Eventually, rover measurements and physical samples collected from Mars could verify whether the soil classes the models predict are actually present in the locations the maps indicate.

The current classification system has acknowledged gaps. It does not yet account for perchlorate toxicity, nitrogen availability, or detailed depth profiles. Many of the input properties are inferred from orbital data and relationships observed on Earth, so the system will require revision as direct measurements from Mars improve. Yet the framework itself offers something scientists have lacked: a consistent way to organize and compare the knowledge that each rover mission collects. As Irving observed, every mission adds valuable information, but without a shared language and structure, that knowledge remains scattered. This system provides a foundation that can grow and evolve as new data arrives.

The work may also illuminate some of Earth's most difficult landscapes. Soils in the Atacama Desert, the Pilbara region of Australia, and various polar zones contain very little organic matter, yet they function as soil. McBratney noted that many people assume soil requires abundant organic matter to work, but Martian research—which deals with soil that contains no organic matter at all—prompts scientists to reconsider what soil fundamentally is and how to work with Earth's own sparse, challenging landscapes.