A9. The Quads – South Mid Latitudes

Relief framework. The belt mixes highland plateaus (Noachis, Sirenum, Aonia) with giant basins (Hellas, Argyre). Basins create pressure bowls that influence local weather and sediment routing.

Climate tendency. Mars’ orbital eccentricity places southern summer near perihelion: summers are shorter and dustier; winters are longer/colder with widespread CO₂ frosts.

Common surface processes. Aeolian: dune fields in many crater floors; yardangs in weakly indurated deposits; dust mantles wax and wane with storms. Periglacial: mantles, polygonal ground, lobate debris aprons, and lineated valley fill—evidence for ground-ice-assisted creep. Mass wasting: landslides and gully activity on steep crater and basin rims.

Lighting & visibility. Haze and dust frequently mute contrasts; in basins (Hellas/Argyre) dust surges can dim midday almost to twilight, while clear spells yield stark, high-relief vistas.

⬛ Tau (τ) (30–72°S, 0–60°E)

Profile. Western Noachis Terra and parts of Terra Cimmeria: classic ancient highlands sloping toward the Hellas rim to the east. A showcase of heavily cratered uplands, dune-filled crater floors, and periglacial mantles.

Relief & elevation. Broad upland plateaus ~1–3 km above the areoid with kilometer-scale crater rims and intercrater benches; local relief subdued compared with canyon provinces but extensive in area.

Geology & landforms. Crater fields with lobate ejecta, pedestal craters, and interior landslides. Dune basins (e.g., Kaiser, Rabe) with extensive barchan/transverse dunes; dark sands sourced from basaltic units. Mantling deposits and polygonal ground indicative of ice-rich regolith at mid–high southern latitudes.

Surface texture. Mix of dust-mantled intercrater plains, yardang patches in weakly indurated layers, and dark dune seas in crater floors.

Temperature & “weather” feel. Large diurnal swings; frequent seasonal CO₂ frost on pole-facing slopes; dust hazes common but vary sol-to-sol.

Distinctives. Abundance of classic dune-filled craters in a highland setting; western approach to the Hellas rim system begins along Tau’s eastern longitudes.

⬛ Upsilon (υ) (30–72°S, 60–120°E)

Profile. The Hellas Planitia basin and surroundings: the deepest, broadest impact depression on Mars, ringed by rugged mountain chains (Hellespontus, Malea) and backed by Promethei Terra to the east.

Relief & elevation. Hellas floor drops to roughly −7 to −8 km relative to the datum; rim systems rise several kilometers above adjacent plains—among Mars’ strongest pressure/altitude contrasts over regional scales.

Geology & landforms. Multi-ring basin architecture with interior plains, wrinkle ridges, and dust/sand mantles. Alluvial fans, gullies, and mass-wasting aprons along steep rim slopes; abundant aeolian bedforms on the basin floor. Glacial/periglacial signatures on the southern/eastern flanks (mantled terrains, lineated valley fills).

Surface texture. Smooth to gently undulating basin plains with patchy dark sand sheets; rough, blocky rim uplands with talus and scarps.

Temperature & “weather” feel. Hellas’ higher ambient pressure and depth moderate extremes slightly; strong dust-storm activity can reduce daylight dramatically; nights often warmer during dusty spells due to IR back-radiation.

Distinctives. The pressure bowl of Hellas is unique, with climate and sediment systems strongly organized by the basin topography.

⬛ Phi (φ) (30–72°S, 120–180°E)

Profile. Eastern Terra Cimmeria merging into the western Phaethontis region: old cratered plateaus with widespread slope gullies, mantled terrains, and tectonic fabrics linking into Sirenum structures to the east.

Relief & elevation. Highlands ~1–3 km above datum with dissected crater fields; local escarpments and mesas give kilometer-scale relief.

Geology & landforms. Gully-rich slopes on mid-latitude crater walls (arcuate alcoves, incised channels, apron deposits). Lineated valley fill and lobate debris aprons consistent with ice-assisted creep. Faults/graben trending NW–SE in places, tying into broader Tharsis-related stresses.

Surface texture. Dust-mantled intercrater plains, rubble-covered slopes, and small dark-sand patches in basin lows.

Temperature & “weather” feel. Strong day–night thermal range; seasonal CO₂ frosting; frequent dust-devil tracks on smoother plains after storm seasons.

Distinctives. One of the canonical gully belts of Mars—dense examples on equator-facing and pole-facing crater walls across this longitude span.

⬛ Chi (χ) (30–72°S, 180–240°E)

Profile. Central Terra Sirenum: densely cratered Noachian crust with classic gully locales (e.g., Newton Crater sector), Sirenum Fossae extensional fabrics, and possible ancient basin remnants toward the Eridania province.

Relief & elevation. Plateau highs with broad uplands and deep craters; typical surfaces ~1–2+ km above the datum, stepping down toward older basin lows.

Geology & landforms. Newton Crater region: textbook gully systems, dune fields on floors, and mass-wasting scarps. Sirenum Fossae: long, narrow graben reflecting crustal extension. Eridania-margin terrain (north/east edge of quad): subdued basins and layered remnants interpreted as ancient, volatile-rich deposits.

Surface texture. Mixtures of smooth mantles, blocky ejecta aprons, and dark-sand sheets; polygonal ground common on gentle slopes.

Temperature & “weather” feel. Mid-latitude southern regime: pronounced seasonality (short, warm southern summers; long, cold winters) with dust activity peaking around perihelion seasons.

Distinctives. High concentration of slope gullies and tectonic lineations in a single quadrangle, useful for comparative geomorphology.

⬛ Psi (ψ) (30–72°S, 240–300°E)

Profile. Southern flank of Thaumasia into Aonia Terra and Icaria Planum: tectonized highlands south of Valles Marineris with corridors of chaos/tectonic troughs, cratered plateaus, and widespread aeolian veneers.

Relief & elevation. Uplands grading from the elevated Thaumasia rise to lower plateaus; canyon-adjacent scarps and benches introduce multi-kilometer local relief.

Geology & landforms. Fractured plateaus with graben and pit chains radiating from Tharsis stresses. Chaos and channel heads along the southern Valles Marineris periphery, transitioning to highland basins. Crater interiors with layered deposits and dune fields.

Surface texture. Rockier erosional benches near troughs; dust/sand mantles and megaripples across plains; yardangs in weakly indurated units.

Temperature & “weather” feel. Topographic channeling yields gusty afternoons; frequent dust hazes reduce contrast. Southern-summer perihelion boosts dust-storm probability.

Distinctives. A meeting ground of Tharsis-related tectonics, canyon-margin processes, and classic highland crater geomorphology.

⬛ Omega (ω) (30–72°S, 300–360°E)

Profile. Argyre Planitia and surrounds: a large, deep impact basin (second only to Hellas) encircled by rugged ranges (Nereidum, Charitum Montes) and draining toward Chryse via outflow systems to the north.

Relief & elevation. Argyre floor sits ~−5 to −6 km below the datum; encircling mountains rise several kilometers above the plains—steep rims, deep basins, and broad interior plains create dramatic relief.

Geology & landforms. Multi-ring basin architecture with interior plains, wrinkle ridges, and lobate deposits. Alluvial fans, gullies, and mass-wasting along the mountainous rim; periglacial mantles common at these latitudes. Nearby craters (e.g., Proctor, Galle) host extensive dune fields and layered intracrater deposits.

Surface texture. Smooth, low-albedo plains on the basin floor; blocky, talus-rich highlands around the rim; prominent dark-sand seas inside larger craters.

Temperature & “weather” feel. As with Hellas, the basin geometry affects local winds and pressure; dust activity can swing lighting from crisp to sepia-hazy over days. Winter brings recurring CO₂ frost on pole-facing slopes.

Distinctives. The “paired-basin” counterpart to Hellas: smaller and shallower, but equally instructive for basin-scale climate and sediment circulation at southern mid-latitudes.