What is the Exoplanet Habitability Calculator?

Estimate whether an exoplanet could support liquid water with this free exoplanet habitability calculator. Enter stellar mass or luminosity, orbital distance, planet radius and mass, and albedo to get habitable zone bounds, stellar flux, equilibrium temperature, and Earth Similarity Index (ESI). Includes presets for Earth, Proxima Centauri b, Kepler-186f, and hot Jupiters. Runs entirely in your browser with no signup.

How to use the Exoplanet Habitability Calculator

Choose a star input mode: stellar mass (luminosity from L ∝ M^3.5) or direct luminosity in solar units.
Enter orbital distance in AU, planet radius and mass (Earth = 1), and Bond albedo (Earth ≈ 0.3).
Click Calculate to see conservative habitable zone inner/outer edges, received flux, equilibrium temperature, and ESI.
Try example presets such as Earth, Proxima Centauri b, or Kepler-186f to compare known worlds.
Use results to judge whether the planet sits in the liquid-water zone and how Earth-like it is on a 0–1 scale.

Common use cases

Screening exoplanet candidates for liquid-water potential in astronomy coursework
Comparing Proxima Centauri b or Kepler-186f to Earth using ESI and HZ placement
Estimating equilibrium temperature for a planet at a given AU from a Sun-like star
Teaching habitable zones and the difference between flux, temperature, and true habitability
Quick checks when reading NASA Exoplanet Archive or PHL data for new discoveries

Frequently asked questions

What is the habitable zone?: The habitable zone (HZ) is the range of orbital distances where a planet could sustain liquid water on the surface, given the star's luminosity. This tool uses a conservative HZ: inner edge at √(L/1.1) AU and outer edge at √(L/0.53) AU.
How is equilibrium temperature calculated?: T_eq ≈ 278 × L^0.25 / d^0.5 × (1 − A)^0.25 K, where L is stellar luminosity (solar), d is orbital distance (AU), and A is Bond albedo. This assumes zero greenhouse effect and rapid rotation.
What is the Earth Similarity Index (ESI)?: ESI is a 0–1 score comparing radius, mass, escape velocity, and equilibrium temperature to Earth using a geometric mean. Values above ~0.8 suggest a potentially Earth-like world; lower values indicate less similarity.
Does a planet in the HZ guarantee life?: No. Being in the habitable zone is necessary but not sufficient — atmosphere, magnetic field, tidal locking, stellar activity, and composition all matter. This calculator provides a first-order screening tool only.
Why use stellar mass instead of luminosity?: Mass is often reported for exoplanet host stars. For main-sequence stars, luminosity scales roughly as M^3.5, which this tool uses when you enter mass in solar units.

More Scientific Tools

What is the Exoplanet Habitability Calculator?

How to use the Exoplanet Habitability Calculator

Choose a star input mode: stellar mass (luminosity from L ∝ M^3.5) or direct luminosity in solar units.

Enter orbital distance in AU, planet radius and mass (Earth = 1), and Bond albedo (Earth ≈ 0.3).

Click Calculate to see conservative habitable zone inner/outer edges, received flux, equilibrium temperature, and ESI.

Try example presets such as Earth, Proxima Centauri b, or Kepler-186f to compare known worlds.

Use results to judge whether the planet sits in the liquid-water zone and how Earth-like it is on a 0–1 scale.

Common use cases

Screening exoplanet candidates for liquid-water potential in astronomy coursework

Comparing Proxima Centauri b or Kepler-186f to Earth using ESI and HZ placement

Estimating equilibrium temperature for a planet at a given AU from a Sun-like star

Teaching habitable zones and the difference between flux, temperature, and true habitability

Quick checks when reading NASA Exoplanet Archive or PHL data for new discoveries

Frequently asked questions

What is the habitable zone?

The habitable zone (HZ) is the range of orbital distances where a planet could sustain liquid water on the surface, given the star's luminosity. This tool uses a conservative HZ: inner edge at √(L/1.1) AU and outer edge at √(L/0.53) AU.

How is equilibrium temperature calculated?

T_eq ≈ 278 × L^0.25 / d^0.5 × (1 − A)^0.25 K, where L is stellar luminosity (solar), d is orbital distance (AU), and A is Bond albedo. This assumes zero greenhouse effect and rapid rotation.

What is the Earth Similarity Index (ESI)?

ESI is a 0–1 score comparing radius, mass, escape velocity, and equilibrium temperature to Earth using a geometric mean. Values above ~0.8 suggest a potentially Earth-like world; lower values indicate less similarity.

Does a planet in the HZ guarantee life?

No. Being in the habitable zone is necessary but not sufficient — atmosphere, magnetic field, tidal locking, stellar activity, and composition all matter. This calculator provides a first-order screening tool only.

Why use stellar mass instead of luminosity?

Mass is often reported for exoplanet host stars. For main-sequence stars, luminosity scales roughly as M^3.5, which this tool uses when you enter mass in solar units.