Exoplanet Discovery Calculator

An exoplanet is any planet that orbits a star outside our solar system. As of 2024, over 5,600 confirmed exoplanets have been discovered across thousands of stellar systems. They vary enormously — from scorching hot Jupiters orbiting closer than Mercury to Earth-sized worlds in habitable zones.

When a planet passes in front of its host star from our viewpoint, it blocks a small fraction of the star's light. This fractional dimming — the transit depth δ — equals the square of the ratio of planet radius to star radius (δ = (Rp/R★)²). Measuring δ and knowing R★ lets astronomers calculate the planet's size.

The radial velocity (Doppler wobble) method detects the gravitational tug a planet exerts on its star, causing the star to move slightly toward and away from Earth. This motion produces measurable Doppler shifts in the star's light. Michel Mayor and Didier Queloz used this technique to discover 51 Pegasi b in 1995 — the first confirmed exoplanet orbiting a Sun-like star — earning the 2019 Nobel Prize in Physics.

Equilibrium temperature estimates the surface temperature a planet would reach if it absorbed and re-radiated all incoming stellar energy, assuming no greenhouse effect. It depends on the star's luminosity, the planet's orbital distance, and its Bond Albedo. A planet's equilibrium temperature falling between roughly 200–320 K suggests it could potentially host liquid water.

Bond Albedo (A) is the fraction of total incoming starlight that a planet reflects across all wavelengths. A value of 0 means the planet absorbs all light (maximum heating); a value of 1 means it reflects everything (no heating). Earth's albedo is about 0.3, Venus is around 0.77. Higher albedo planets are cooler; lower albedo planets are warmer.

Orbital eccentricity (e) measures how elliptical an orbit is. A circular orbit has e = 0; an eccentricity near 1 is highly elongated. Eccentricity affects both the radial velocity signal shape and the planet's temperature variations over its orbit. The radial velocity semi-amplitude is scaled by the factor 1/√(1 − e²), so more eccentric orbits produce larger detectable signals.

Radial velocity measures only the component of the star's motion along our line of sight. If the orbit is viewed edge-on (inclination i = 90°), we see the full Doppler signal. At lower inclinations, we only observe a fraction (sin i) of the true stellar velocity. This means radial velocity gives a minimum planet mass (Mp × sin i) unless the inclination is independently known from transit observations.

Over 5,600 confirmed exoplanets have been found as of 2024. The transit method (primarily via NASA's Kepler and TESS missions) accounts for roughly 75% of discoveries. Radial velocity found another ~20%, with direct imaging, gravitational microlensing, and astrometry accounting for the remainder. Most known exoplanets were found by combining multiple methods.