Exoplanet Habitability Score

Calculate the Earth Similarity Index (ESI) for an exoplanet based on radius, density, escape velocity, and surface temperature relative to Earth.

Inputs

Planet Radius

R⊕

Planet Density

ρ⊕

Escape Velocity

V⊕

Surface Temperature

Tab to move between fields

Results

Earth Similarity Index

Classification

Earth-like

Interior ESI1

Surface ESI1

Surface Gravity1 g⊕

Surface Temperature14.9 °C

Water StateLiquid (possible)

How to Use This Calculator

Enter Planet Radius (R⊕) relative to Earth — values near 1.0 indicate a rocky, Earth-sized world.
Enter Planet Density (ρ⊕) relative to Earth's 5,515 kg/m³ to characterize interior composition.
Enter Escape Velocity (V⊕) relative to Earth's 11.2 km/s — this determines ability to retain an atmosphere.
Enter Surface Temperature (K): Earth is 288 K; values between 273 K and 373 K allow liquid water.
Read the Earth Similarity Index (ESI) from 0 to 1 — values above 0.8 are considered Earth-like, and check Water State for habitability clues.

How the result changes with Surface Temperature

Surface Temperature	Earth Similarity Index	Classification
209	0.8852	Earth-like
707	0.6804	Potentially Habitable
1,304	0.4886	Marginally Habitable
1,801	0.4035	Marginally Habitable

What each input means

Planet Radius: Planet radius in Earth radii (Earth = 1, Mars = 0.53, Jupiter = 11.2)
Planet Density: Bulk density relative to Earth (Earth = 1 = 5,515 kg/m³, Mars = 0.71)
Escape Velocity: Escape velocity relative to Earth (Earth = 1 = 11.2 km/s, Mars = 0.45)
Surface Temperature: Estimated equilibrium surface temperature in Kelvin (Earth = 288 K, Mars = 210 K)

How this is calculated

Formula

ESI = ∏(1 - |xᵢ - xᵢ₀| / (xᵢ + xᵢ₀))^(wᵢ/n)

Worked example, using the default values

Identify Input Parameters
4 parameters
Planet Radius = 1, Planet Density = 1, Escape Velocity = 1, Surface Temperature = 288 = 4 input(s) provided
Calculate Earth Similarity Index
Earth Similarity Index
1 = 1
Calculate Classification
Earth-like = Earth-like
Calculate Interior ESI
Interior ESI
1 = 1
Calculate Surface ESI
Surface ESI
1 = 1

Engine last updated July 21, 2026. Checked against 2 independently-derived tests — how we verify calculators.

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