First map of Martian soils sorts the planet into 2,000 soil types
A University of Sydney PhD student classified almost 800 million points on Mars seen from orbit. The best-scoring soil for growing plants covers just 0.14% of the surface, and the authors stress these are areas to study, not chosen greenhouse sites.
Almost 800 million points on the surface of Mars, observed from orbit, have been sorted into 2,000 soil types. It is the first full system for classifying the red planet’s soils, and its map covers 92% of the surface.
The work, by soil scientist Alex McBratney and his PhD student Daniel Irving at the University of Sydney, was published on 7 October in the journal Catena. “This is the first time a classification system of this scale has been developed for Martian soils,” Irving said in the university’s release.
A new word: “areths”
On Earth, soils are classified mostly by their layers below ground, but there is no layer-by-layer data for Mars. So the team worked from surface properties and coined a new term, “areth”, from Ares, the Greek name for Mars. The system has three tiers: 10 realms, 100 assemblages and 2,000 forms.
One soil scores 0.93 out of 1
As a test, the researchers scored every class on how well it might grow plants: water-holding capacity, pH, thickness, clay and gravel. The best, called “Nohibareth”, scored 0.93 out of 1. It covers about 0.14% of the surface, mainly in mid-latitude regions such as Tharsis, central Arabia Terra and Elysium Planitia. In 73% of the forms assessed, water-holding capacity was the main limit.
What the map can’t see yet
The authors stress that these areas are candidates for closer study, not chosen greenhouse sites. The map does not yet account for toxic perchlorates, available nitrogen or how soils change with depth. “A future greenhouse on Mars would need more than air, water and light,” McBratney said.
Next, the team plans to test Mars-like substrate mixes in controlled experiments on Earth. They also expect the work to help explain low-organic soils here, such as those of the Atacama Desert and Australia’s Pilbara.
