A University of Sydney researcher has used Mars orbital and model data to create the world’s first map of Martian soil covering roughly 92% of the red planet’s surface.
The PhD student behind the first-of-its-kind Mars soil map said the work, which includes a soil-growing viability scoring system, could give future Martian colonists and research bases a list of the best locations for establishing greenhouses that take advantage of local resources.
“This is the first time a classification system of this scale has been developed for Martian soils,” explained Daniel Irving from the Sydney Institute of Agriculture and the Faculty of Science.
Martian Soil Separated into 2,000 Classes
To build his Martian soil map and grading system, Irving drew on a wide array of existing resources. This included orbital observations from Martian satellites and planetary models based on data gathered from rovers and other scientific studies of the red planet.
After combining the data, Irving classified 800 million individual locations across the Martian surface. This included separating the locations into 2,000 soil “classes” and marking where these soils are expected to be found.
Next, Irving and his supervisor, Professor Alex McBratney, evaluated each class’s properties, including texture, mineralogy, profile thickness, and pH level. This granular detail allowed them to group the soil classes into 10 major “realms,” 100 “assemblages,” and 2,000 “detailed forms,” resulting in what they called the Provisional Polythetic Areth Classification System, or PPACS.
According to a release announcing the work, the Sydney researcher and his supervisor proposed the term “areths,” which they derived from Ares, the Greek name for Mars, for these new Martian soil classes.
PPACS Scores Mark Best Locations for Future Mars Greenhouses
After classifying the 2,000 soil types on the PCCS, the Sydney team assessed each one for characteristics that are known to support plant production on Earth. These included the soil’s capacity for holding water and how much clay and gravel it contained.
“A future greenhouse on Mars would need more than air, water, and light. Its builders would also need to know what lies beneath to understand better starting points for growing plants,” Professor McBratney explained.
After examining the results, Irving and colleagues found one class, which they named Nohibareth, offered the best collection of plant growth-supporting properties. As a result, Nohibareth received a PCCS score of 0.93, ranking it at the top of the list.
“Nohibareth’s modeled average profile includes a pH of 6.8, 72 percent clay, minimal sand or gravel, and an estimated water-holding capacity of 202 millimeters per meter,” a statement announcing the research explained.
The Martian Soil map indicates that this preferred class is found around the planet’s middle latitudes, including around Tharsis, central Arabia Terra, and Elysium Planitia. However, this soil type is only found on 0.14 percent of the planet’s surface.
Although other soils showed some promise, the researchers found that 73 percent of the forms they evaluated had poor water retention properties, making them unlikely soil bases for plant growth. For example, the researchers noted that classes in the Fareth to Mareth realms all scored below 0.3 on the PCSS, “reflecting less favorable combinations of the properties considered.”
Candidates for Closer Investigation
When discussing the study’s results, Irving and colleagues cautioned that the highlighted Nohibareth sites are not already selected for future greenhouses. Instead, they said the areas on their map suggesting the best plant-growing Martian regolith represent “candidates for closer investigation.”
The Sydney team also warned that Martian soil contains no organic compounds and that their findings do not suggest crops can be grown even in the highest-scoring material. They also note that the map does not include factors that can affect plant growth, such as perchlorate toxicity, nitrogen availability, or depth profiles.
However, Irving and colleagues said the map and scoring system suggest that colonists could supplement the highest-scoring Martian soils and use them in controlled environments to potentially create self-sustaining greenhouses that don’t require regular supplies from Earth. Irving said their findings could also offer a new way to interpret the data scientists regularly receive from ongoing Mars missions.
“Every rover mission collects valuable information about Mars, but scientists need consistent ways to organize and compare that knowledge,” he explained. “This gives us a framework that can grow and evolve as new data becomes available.”
The study was published in the soil science journal Catena.
Christopher Plain has spent the last six years as Associate News Editor and Head Science Reporter at The Debrief. Follow and connect with him on X, learn about his novels at plainfiction.com, or email him at christopher@thedebrief.org.