A1. Mars Planet Surface
Summary. Mars is a smaller world than Earth—about half Earth’s diameter—but because it lacks global oceans, its entire surface is land.
The result is a memorable rule of thumb: Mars’ total surface area (~145 million km²) is roughly equal to the area of all Earth’s continents combined (~149 million km²).
The Moon, by contrast, is far smaller, with only ~38 million km² of surface—about one-quarter of Mars.
Planetary dimensions at a glance
Mean radius (km): Earth 6,371 | Mars 3,390 | Moon 1,737.
Diameter (km): Earth 12,742 | Mars 6,779 | Moon 3,474.
Equatorial circumference (km, approx.): Earth 40,075 | Mars ~21,000 | Moon ~10,900.
Surface gravity (m·s⁻²): Earth 9.81 | Mars 3.71 | Moon 1.62.
Numbers from NASA fact pages and standard references.
What the size means in practice
Map scale & travel distance – A transcontinental trek on Earth (say, 5,000 km) corresponds to a similar long-haul traverse on Mars; planet-spanning missions there are genuinely intercontinental in scope. The equatorial lap of Mars is roughly ~21,000 km—a little over half of Earth’s—so great-circle trips are shorter, but still planetary in scale.
Horizon distance (human “feel”) – For an eye height ~1.7 m, the geometric horizon on Earth is ~4.7 km; on Mars it’s ~3.4 km (smaller radius curves away sooner), so the horizon feels closer, with landforms dropping below it more quickly.
Gravity context – Mars’ surface gravity is ~0.38 g (about ⅓ of Earth’s), while the Moon’s is ~0.17 g. This doesn’t change area, but it changes how terrain is experienced—from how far dust is lofted to how easily a rover (or person) can climb a slope.
Domain | Mars Reality | Primary Implications |
Air & Pressure | ~95% CO₂; 0.6–0.8 kPa lowlands; higher in deep basins | EVA is always pressurised; suit design favors dust sealing over wind load; boiling point constraints for fluids |
Light & Visibility | TOA ~590 W/m² (~43% Earth); τ 0.3→5+ governs ground light; blue sunsets, amber days | Power planning by τ; lighting as psychology and protocol; operations shift toward mornings/clear windows |
Wind & Abrasion | Gusts 25–30 m/s common aloft; low dynamic pressure; active sand saltation | Structural shove modest; abrasion/infiltration dominant; sacrificial skins, replaceable “eyebrows,” frequent cleaning |
Temperature & Thermal | Mean ~210 K; large diurnal swings; basins milder, plateaus harsher | Radiative & ground-coupled thermal design; trenching; radiator scheduling; heat treated as inventory |
Sound & Comms | ~240–250 m/s; frequency-dependent speeds; strong attenuation | Acoustic cues unreliable outdoors; visual & haptic signaling favored; door-tones and pressure chimes standard |
Weather & Storms | No rain; frost/CO₂ snow; local/regional storms; planet-encircling veils episodic | Convoy spacing by visibility; storm playbooks; storage and non-solar baseload mandatory |
Seasons & Pressure Tide | ~25–30% atmospheric CO₂ migrates poleward each winter | Barometric planning baked into rota; valve scheduling; calendar aligned to pressure reality |
Landscape & Mobility | Plains, canyonlands, crater floors, lava aprons, polar plateaus | Route grading; inversion hazards; dust pools; honest maps and conservative reach rings |
Dust & Cleanliness | Micron-scale fines; electrostatic adhesion; persistent lofting | Design for cleanability; filter life as KPI; coatings wear tracking; dust-lock etiquette as civic norm |