A PhD student at the University of Sydney has created the first comprehensive classification system for Martian soils, mapping 2000 distinct soil types across 92% of Mars’ surface to aid future exploration and potential agriculture.
Daniel Irving, a PhD candidate at the University of Sydney’s Sydney Institute of Agriculture, has developed the Provisional Polythetic Areth Classification System (PPACS), the first framework to categorize Martian soils into 10 major “realms,” 100 “assemblages,” and 2000 detailed “forms” based on properties like texture, pH, and profile thickness. Published in the journal Catena, the research uses orbital data to map nearly 800 million locations, offering a tool for scientists to compare Martian landscapes and identify promising areas for future habitation or crop growth.
Mapping Martian Soils for Future Missions
The PPACS system, described as the first time a classification system of this scale has been developed for Martian soils,
integrates multiple properties into a single framework. “Scientists have mapped Mars’ geology, mineralogy, and chemistry before, but our system brings together multiple properties into a single framework, helping us understand how different Martian soils relate to one another and where they’re found,” Irving said. The classification is accompanied by a map covering 92 percent of the Martian surface.
Nohibareth: A Top Soil Candidate
Among the 2000 soil classes, Nohibareth emerged as the most promising, scoring 0.93 on the study’s zero-to-one grading scale. Modeled after data from the mid-latitudes of Mars, including regions like Tharsis and Elysium Planitia, Nohibareth has a pH of 6.8, 72 percent clay, and an estimated water holding capacity of 202 millimetres per metre. However, researchers stress that this does not mean crops could be grown directly in Martian soil. Future habitats would still require controlled environments, water, nutrients and treatment of potentially harmful substances.
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,
said Irving’s supervisor, Professor Alex McBratney. The study highlights that water holding capacity was the limiting factor in 73 percent of forms studied, with classes in the Fareth to Mareth regions all scoring below 0.3 in this initial test.
Insights for Earth’s Harsh Regions
The research may also help soil scientists better understand some of Earth’s most challenging landscapes such as Atacama Desert, the Pilbara region and various polar regions. People often think soil needs lots of organic matter to function, but there are soil types on Earth, particularly in arid regions, that contain very little organic matter,
McBratney said. The findings could inform strategies for managing challenging terrestrial landscapes.
Irving emphasized that the classification system is designed to evolve with new data. Every rover mission collects valuable information about Mars, but scientists need consistent ways to organise and compare that knowledge,
he said. Future work may involve testing Mars-like soil mixtures on Earth and verifying mapped classes through rover measurements and samples.
The study’s framework could also aid in selecting landing sites for future missions. While Nohibareth soils are found on 0.14 percent of Mars’ surface, their distribution in mid-latitude regions makes them candidates for closer investigation. However, the research does not address factors such as perchlorate toxicity, nitrogen availability or depth profiles.