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Architecture

System Overview

The Moon is a differentiated silicate body with a layered internal structure, asymmetric crust, and minimal active geology. It operates as a tidally locked satellite in a stable Earth orbit.

Internal Structure

┌─────────────────────────────────────────┐
│           Crust (60–100 km)             │  ← Anorthosite (highlands) / Basalt (maria)
│         ┌─────────────────┐             │
│         │   Near Side     │  ~30 km     │  ← Thinner, more mare flooding
│         │   Far Side      │  ~60 km     │  ← Thicker, fewer maria
│         └─────────────────┘             │
├─────────────────────────────────────────┤
│         Mantle (~1,000 km)              │  ← Olivine, pyroxene cumulates
│  ┌─────────────────────────────────┐    │
│  │   Partial Melt Zones (legacy)   │    │  ← Rare, localized (v2.2.x patches)
│  └─────────────────────────────────┘    │
├─────────────────────────────────────────┤
│         Core (~350 km radius)           │  ← Partially molten? Fe-rich
│         ┌─────────────────┐             │
│         │  Solid Inner?   │  (debated)  │
│         │  Liquid Outer?  │  (debated)  │
│         └─────────────────┘             │
└─────────────────────────────────────────┘

Crust Layer

  • Highlands: Anorthosite (90%+ plagioclase), bright, heavily cratered. Formed via magma ocean flotation (v0.3.0-beta).
  • Maria: Basaltic, dark, iron-rich. Formed via mantle partial melting and flood volcanism (v1.1.0–v1.4.0).
  • Asymmetry: Far side crust is ~2× thicker than near side. Possible causes:
    1. Second Moon Impact: A smaller companion moon may have collided with the far side early in history (v0.3.x). Note: GRAIL data has challenged some aspects of this model.
    2. Tidal Effects: Near side experienced stronger tidal forces from Earth, thinning the crust.
    3. PKT Enrichment: Procellarum KREEP Terrane on near side concentrated heat-producing elements, promoting volcanism and crustal modification.

Mantle Layer

  • Upper Mantle: Olivine-pyroxene cumulates from magma ocean crystallization.
  • Lower Mantle: Dense ilmenite-rich cumulates. May have sunk during mantle overturn (v1.0.0 era).
  • Partial Melt: Rare in modern era. Chang'e 5 samples (v3.0.2) prove mantle was still capable of melting at ~1.2–2.0 Ga. Irregular Mare Patches (v2.2.3) suggest melting as recent as 100 Ma.

Core Layer

  • Radius: ~350 km (20% of lunar radius).
  • State: Likely partially molten. Evidence from magnetic induction and seismic data.
  • Magnetic Field: No active dynamo. Weak crustal magnetic anomalies remain from ancient dynamo (~4.2–3.5 Ga).

Surface Architecture

Regolith

  • Thickness: 5–10 meters (maria vs. highlands).
  • Composition: Impact-generated rubble, rock fragments, glass beads, agglutinates.
  • Properties: Extremely abrasive, poor heat conductivity, high porosity.
  • Challenges: Electrostatic levitation, dust adhesion, thermal cycling damage.

Impact Craters

The primary surface modification process in the modern era.

Type Diameter Characteristics
Simple < 15 km Bowl-shaped, raised rim
Complex 15–300 km Central peak, terraced walls
Peak-Ring > 100 km Inner ring of peaks
Multi-Ring > 300 km Multiple concentric rings (basins)

Tectonic Features

  • Lobate Scarps: Reverse faults from global contraction. Thousands identified, many recently discovered (2026).
  • Rilles: Sinuous (lava channels), arcuate (basin edge), straight (graben).
  • Graben: Tensional features, often near basin margins.

Thermal Evolution

Time (Ga)    Temperature    State
─────────────────────────────────────────
4.51         > 2,000 K      Magma ocean
4.50         ~1,800 K       Rapid crystallization
4.46         ~1,500 K       First crust
4.4          < 1,200 K      Solid crust stable
3.9          ~1,400 K       Mare volcanism peak
3.2          < 1,200 K      Major volcanism ends
2.0          ~1,100 K       Localized melting (Chang'e 5)
0.1          ~1,000 K       Irregular Mare Patches
Now          ~900 K         Cooling, contracting

Data Flow

Sunlight → Lunar Surface → Reflected Light → Earth Observers
                    ↓
              Absorbed Heat → IR Emission
                    ↓
              Thermal Cycling → Mechanical Stress → Moonquakes
                    ↓
              Solar Wind → Sputtering → Exosphere (trace)

Known Design Decisions

  1. No Atmosphere: Intentional. Lunar escape velocity (2.38 km/s) is too low to retain gases at surface temperature. Also, atmosphere would obscure impact record.
  2. Tidal Lock: System requirement. Conserves angular momentum in Earth-Moon system. Enables stable long-term orbit.
  3. Synchronous Rotation: Side effect of tidal lock. One face always toward Earth. Enables continuous Earth communication from near side.
  4. Regolith Preservation: Trade-off. No erosion means 4.5 billion year impact record is preserved, but surface is hazardous to machinery.

Performance Characteristics

  • Orbital Period: 27.32 days (sidereal), 29.53 days (synodic)
  • Rotation Period: 27.32 days (synchronous)
  • Surface Temperature Range: -173°C to 127°C
  • Seismic Activity: ~600 moonquakes/year (detectable by Apollo network)
  • Impact Rate: ~1 ton/day of micrometeoroids
  • Mass Loss: Negligible (no atmosphere to escape, no volcanic outgassing)
  • Orbital Evolution: +3.8 cm/year semi-major axis increase; orbital period +0.00000002 days/year

For API documentation, see API.md.