Stellar Habitable Zone Calculator
Calculate the inner and outer edges of a star's habitable zone — where liquid water can exist on a planet's surface.
Enter luminosity or radius and temperature.
The habitable zone (HZ) — sometimes called the Goldilocks zone — is the range of orbital distances around a star where liquid water could exist on a rocky planet’s surface, given sufficient atmospheric pressure.
Conservative habitable zone boundaries:
Inner edge: r_inner = √(L / 1.1) AU
Outer edge: r_outer = √(L / 0.53) AU
Where L is the stellar luminosity in solar units (L☉).
Optimistic boundaries extend this slightly:
r_inner (optimistic) = √(L / 1.776) AU
r_outer (optimistic) = √(L / 0.32) AU
These are based on the Kopparapu et al. (2013) model.
For our Solar System:
- Sun (1 L☉): conservative HZ from 0.95 to 1.37 AU
- Earth (1.0 AU) sits comfortably inside
- Mars (1.52 AU) is just outside the conservative but inside the optimistic HZ
From luminosity using radius and temperature: If you know radius R (in R☉) and temperature T (in K):
L = (R/R☉)² × (T/5778)⁴
Important caveats: The habitable zone is not a guarantee of habitability. Mars is in the optimistic HZ but lacks a thick atmosphere. Venus is just inside the inner edge but has a runaway greenhouse. Factors like magnetic field, tidal locking, stellar activity, and atmospheric composition all matter. Moons of giant planets (like Jupiter’s Europa) could also harbor liquid water outside the traditional HZ.