Exoplanet Properties Calculator

The main detection methods are: transit photometry (the planet crosses the star's disk, dimming it slightly), radial velocity (the planet's gravity causes the star to wobble toward and away from us), direct imaging (photographing the planet separately from its star), gravitational microlensing, and astrometry (measuring the star's position wobble). The Kepler and TESS missions have discovered thousands of exoplanets via transits.

The equilibrium temperature is the temperature a planet would reach if it absorbed all incoming stellar radiation and re-emitted it as thermal blackbody radiation, assuming a Bond albedo (reflectivity). For Earth, this is about 255 K. The actual surface temperature is higher due to the greenhouse effect, which traps outgoing longwave radiation.

Many factors matter beyond orbital distance: atmospheric composition and pressure, presence of liquid water, the planet's mass (affects whether it can hold an atmosphere), plate tectonics (which recycles carbon and regulates long-term climate), magnetic field (which deflects cosmic rays and stellar wind), orbital eccentricity (which affects seasonal temperature swings), and the age and activity level of the host star.

Hot Jupiters are gas giant planets with masses comparable to Jupiter that orbit very close to their host stars — often within 0.1 AU — giving them orbital periods of just a few days. They were among the first exoplanets discovered by radial velocity surveys but are absent from our Solar System. Their origin is debated: they may have formed farther out and migrated inward due to gravitational interactions with the protoplanetary disk.

Statistical surveys of exoplanet sizes have revealed a gap in the distribution around 1.5-2 Earth radii. Planets below this size tend to be rocky super-Earths, while those above are gaseous mini-Neptunes. This radius gap, known as the Fulton gap, is thought to result from photoevaporation: intense stellar radiation strips the atmospheres of smaller planets, leaving bare rocky cores, while larger planets retain their gaseous envelopes.

Kepler's third law (P^2 = a^3 / M_star in solar units) allows astronomers to determine the semi-major axis directly from the measured orbital period and the host star's mass. Since the period is observable from transit timing and the stellar mass can be estimated from spectroscopy, the orbital distance follows immediately without needing to measure it directly.

Transit timing variations occur when a transiting planet's orbital period is not perfectly constant due to gravitational perturbations from other planets in the system. By measuring these variations, astronomers can infer the masses and orbits of non-transiting planets — even those too small to detect by other means. TTV analysis has revealed multi-planet systems and confirmed that many Kepler candidates are indeed planets.

As of 2026, candidates for the most Earth-like exoplanets include TRAPPIST-1e and 1f (rocky planets in the habitable zone of an M dwarf 39 light-years away), Kepler-442b (super-Earth in the habitable zone of a K star), and Proxima Centauri b (potentially rocky planet at 1.27 AU from our nearest stellar neighbor). None have confirmed atmospheres yet.

TRAPPIST-1 is a nearby ultra-cool red dwarf with seven known Earth-sized rocky planets, three of which (e, f, g) lie within or near the habitable zone. It demonstrated that compact multi-planet systems around M dwarfs are common. However, M dwarf habitability is controversial because these stars are very active, potentially bombarding their planets with flares and stellar wind that may erode atmospheres.