Sydney PhD student sorts almost 800 million Martian locations into 2,000 soil classes
University of Sydney PhD student Daniel Irving classified almost 800 million Martian locations into 2,000 soil classes, called areths. The scheme is labelled provisional, and its plant-growth ranking still awaits tests on Earth and checks by rover.
The Scientist · Science desk
Nohibareth, the most promising candidate, scored 0.93 on the study's zero-to-one grading scale. Classes in the Fareth to Mareth realms all scored below 0.3 in the initial test. Nohibareth soils are found on 0.14% of Mars' surface.
| Figure | Value | Note | Claim |
|---|---|---|---|
| Nohibareth, most promising candidate, zero-to-one scale | 0.93 score | 8 | |
| Fareth to Mareth realm classes, all below | 0.3 score | initial test | 13 |
| Nohibareth soils on Mars | 0.14% of surface | 11 |
What happened
- The Provisional Polythetic Areth Classification System groups soils into 10 realms, 100 assemblages and 2,000 forms, using texture, mineralogy, pH and profile thickness.
- In a proof-of-concept test for plant production, the class Nohibareth scored highest, at 0.93 on the study's zero-to-one scale.
- Classes in the Fareth to Mareth realms all scored below 0.3 in the same test.
Why it matters
- Who has to decide decision Groups with growth chambers now have a list of classes to reproduce as Mars-like mixtures, and must choose which to build first and which comparisons to run.
- What it limits constraint Perchlorate toxicity, nitrogen availability and depth profiles are missing from the map, so that evidence has to come from elsewhere before any class can be judged usable.
- Who's exposed exposure The placements are model outputs. Only rover measurements or returned samples could confirm that a promising class sits where the map puts it.
The classes are built from orbital observations and models [2]. To show what the scheme can do, the team scored all 2,000 forms on five properties that matter for plant production: water-holding capacity, pH, profile thickness, clay content and gravel content [7]. The top mark is a score on those five properties, on the study's own scale.
The leading class, Nohibareth, has a modeled average profile that is 72% clay with little sand or gravel, a pH of 6.8 and an estimated 202 millimeters per meter of water-holding capacity [9]. The map puts it in the midlatitudes, around Tharsis, central Arabia Terra and Elysium Planitia [10]. It covers 0.14% of the surface [11]. The researchers call these areas candidates for closer investigation, not selected greenhouse sites [18].
Water is the usual weak point. Water-holding capacity was the limiting factor in 73% of forms studied [12]. Across all 2,000 assessed forms, that is about 1,460 [19].
The thing this score doesn't tell you is whether a soil could be farmed as it lies. The researchers stress that it does not mean crops could be grown directly in Martian soil [14]. Future habitats would still need controlled environments, water, nutrients and treatment of potentially harmful substances [15].
"This is the first time a classification system of this scale has been developed for Martian soils," Irving said [20]. "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," he said [21]. His supervisor, professor Alex McBratney, said, "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." [6]
In our view the hierarchy is the durable part of the work and the ranking the perishable part, because a class can be rescored when better inputs arrive. The study notes that many of its inputs are estimated from orbital data and from relationships established on Earth, and that the classification will have to be revised as direct measurements get better [17].
What to watch
- Earth-based growth trials on Mars-like mixtures built from the mapped classes, and whether Nohibareth-type mixtures hold up on plant growth and water use.
- A revised map that adds perchlorate toxicity, nitrogen availability and depth profiles, and whether Nohibareth's 0.93 survives the extra properties.
- Rover measurements or samples from the Tharsis, Arabia Terra and Elysium Planitia areas that test where the models place promising classes.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence50
- Adoption
- Not scored
- Hype gap+20
- Incentives
- Not scored
- Confidence55
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
Daniel Irving, a PhD student at the University of Sydney, led research published in the journal CATENA that classifies almost 800 million locations across Mars into a hierarchy of 2,000 soil classes.
- [2]
The classification uses orbital observations and models.
- [3]
The research proposes the term 'areths', derived from Ares, the Greek name for Mars, for Martian soil classes.
- [4]
The Provisional Polythetic Areth Classification System (PPACS) groups Martian soils into 10 major realms, 100 assemblages and 2,000 detailed forms, based on properties including texture, mineralogy, pH and profile thickness.
- [5]
The classification is accompanied by a map covering 92% of the Martian surface.
- [6]
Irving's supervisor, professor Alex McBratney, said, "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."
- [7]
As a proof of concept, the researchers assessed all 2,000 soil classes for characteristics important to plant production: water-holding capacity, pH, profile thickness, clay content and gravel content.
- [8]
One soil class, Nohibareth, emerged as the most promising candidate, scoring 0.93 on the study's zero-to-one grading scale.
- [9]
Nohibareth's modeled average profile includes a pH of 6.8, 72% clay, minimal sand or gravel and an estimated water-holding capacity of 202 millimeters per meter.
- [10]
The map places Nohibareth particularly in the midlatitudes of Mars, around Tharsis, central Arabia Terra and Elysium Planitia.
- [11]
Nohibareth soils are found on 0.14% of Mars' surface.
- [12]
Among the assessed properties, water-holding capacity was the limiting factor in 73% of forms studied.
- [13]
Classes in the Fareth to Mareth realms all scored below 0.3 in the initial test, reflecting less favorable combinations of the properties considered.
- [14]
The researchers stress that the result does not mean crops could be grown directly in Martian soil.
- [15]
Future habitats would still require controlled environments, water, nutrients and treatment of potentially harmful substances.
- [16]
The current map does not include perchlorate toxicity, nitrogen availability or depth profiles.
- [17]
Many input properties are inferred from orbital data and terrestrial relationships, so the classification will need revision as direct measurements improve.
- [18]
The areas where Nohibareth occurs are candidates for closer investigation, not selected greenhouse sites.
- [19]
Water-holding capacity was the limiting factor in about 1,460 of the 2,000 assessed forms.
- [20]
"This is the first time a classification system of this scale has been developed for Martian soils," Irving said.
- [21]
"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.
- [22]
Next steps would be on Earth: scientists can make or obtain Mars-like substrate mixtures representing the mapped classes and test them in controlled growing spaces with crops, added nutrients and managed water, comparing plant growth, water use and the treatment needed to make each mixture safe.
- [23]
In time, rover measurements and samples from Mars could check whether the promising mapped classes are present where the models place them.
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Sources
1 independent publisher whose own reporting we read for this story.
- phys.orgFirst comprehensive Mars soil classification offers framework for exploration and future farming
1 article · October 16, 2026
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