Martian Regolith from Hellas Basin – A Tree-First Simulant for Large-Scale Greenhouses

“If we ever cover Mars in orchards, the first saplings will have cut their roots in a bucket here on Earth.”

Why Hellas Basin?

Highest natural pressure on Mars – the basin floor sits ~7 km below datum. Wintertime surface pressure reaches ≈ 11–12 mbar, about 2 × the planetary average.
Megadome advantage – for a 200 mbar interior (enough for many temperate trees under high-O₂, low-N₂ mixes) the stress on walls in Hellas is ~5 % lower than at datum and ~10 % lower than on high plateaus. Spread over hundreds of hectares, that translates into thousands of tonnes of saved steel or polymer.
Target crops – not quick leafy greens but full forests and orchards: apple, poplar, birch, pine… Species that lock carbon, build soil, and last decades.

Hence this simulant is tuned first for woody perennials—deep roots, long lifespans—and then for annuals.

Basalt backbone – crush volcanic gravel/“lava rock” to a dust-to-sand mix (< 0.1 mm – 2 mm).
Quartz filler – equal volume of washed quartz sand.
Iron oxide – ~10 % red Fe₂O₃ pigment for chemistry and colour.
Alkalinity buffers – CaCO₃ powder (garden lime, chalk) + a pinch of Mg-sulfate (Epsom salt) to push pH ≈ 8–9.
Clay fraction – 20–30 % bentonite (cheap clumping cat-litter) to boost water-holding capacity for trees.
Trace salts – 1 tsp NaCl + 1–2 Tbsp gypsum per 5 L batch.
Mix, lightly mist to keep dust down, then bake at 120–150 °C for 2–3 h to sterilise.

Safety note – wear a dust mask & gloves when handling fine powders.

Initial test species: dwarf apple (Malus ‘M9’), Scots pine seedlings, Lombardy poplar cuttings.
Log pH, EC, Ca/Mg leaching and root tensile strength.

Region / Use-case	Basaltic Lava Rock (%)	Quartz Sand (%)	Fe₂O₃ Pigment (%)	CaCO₃ (%)	Bentonite Clay (%)	Sulfate Salts (%)	Target pH	Texture / Notes
Arcadia Planitia – fast greens	50	25	10	5	2	5	8.3	Coarse, sand-dominated; drainage > water retention
Hellas Basin – tree orchards	35	20	8	10	15	10	7.5	Finer, clay-rich; mimics aqueous alteration, holds moisture for deep roots

Ingredient	Readily-available products	DIY sourcing
Basaltic Lava Rock	Landscaping mulch, aquarium lava, BBQ stones	Ball-mill basalt driveway gravel
Quartz Sand	Children’s play-sand, pool-filter media	Wash & sieve beach sand
Fe₂O₃ Pigment	Concrete colourant, artists’ red iron oxide	Make rust: soak steel wool in vinegar, dry & grind
CaCO₃	Garden lime, chalk powder	Bake & grind seashells
Bentonite Clay	Unscented clumping cat-litter	Disintegrate pellets, sieve fines
MgSO₄ / CaSO₄	Epsom salt, gypsum plaster	Evaporate bath-grade Epsom, bake drywall scraps
NaCl	Table or sea salt	Solar-evaporate seawater