Habitable Zones
The Goldilocks Zone & Liquid-Water Worlds
Each panel uses its own scale — actual HZ distances span over 4,000× from M-dwarf to O-type. Red dashed ring = inner edge (runaway greenhouse). Blue dashed ring = outer edge (CO₂ glaciation).
The habitable zone is the orbital region where a rocky planet with an Earth-like atmosphere could maintain liquid water on its surface — too close and it boils, too far and it freezes.
The HZ scales with √(L/L☉) because flux falls off as 1/r² and equilibrium temperature scales as the fourth root of flux. A star ten thousand times more luminous pushes the HZ a hundred times further out.
G-type and K-type stars are the sweet spot — long-lived, stable HZs, and Earth-likes form here far more often than around M dwarfs.
In the system map, look for terrestrial bodies at distances roughly equal to the listed HZ range for the parent star's class. ELW, water world, and ammonia world cartographic credits all reward HZ-band finds.
Around binaries, the effective HZ is the combined flux from both stars — a circumbinary ELW must be far from both components.
| Class | Mass (M☉) | Lum. (L☉) | HZ Inner (AU) | HZ Outer (AU) | Year @ HZ | Note |
|---|---|---|---|---|---|---|
| O | ≥16 | 30,000 | 165 | 237 | ~600 yr | Massive, hot, brief — HZ planets are rare |
| B | 2–16 | 1,000 | 30 | 44 | ~70 yr | Hot blue-white, short MS lifetime |
| A | 1.4–2 | 25 | 4.7 | 6.85 | ~10 yr | Bright white; HZ at ~5–7 AU |
| F | 1–1.4 | 3 | 1.65 | 2.40 | ~2 yr | Slightly hotter than Sun, wider HZ |
| G | 0.8–1 | 1 | 0.95 | 1.37 | ~1 yr | Sun analogue — Earth at 1 AU |
| K | 0.45–0.8 | 0.15 | 0.37 | 0.53 | ~0.2 yr | Long-lived, stable HZ — best for life longevity |
| M | 0.08–0.45 | 0.01 | 0.05 | 0.20 | ~21 d | HZ planets often tidally locked; flare risk |