Distance from star

The distance between an exoplanet and its star is one of the most important factors in understanding the planet’s environment. It affects the planet’s temperature, the amount of radiation it receives, and whether it might be habitable. Astronomers often calculate this distance using the planet’s orbital period (how long it takes to complete one orbit) and the mass of the star. With these values, they can apply Kepler’s laws to estimate how far the planet is from its star.

In the Stellar Catalog, this distance is shown in astronomical units (AU). One AU is the average distance between Earth and the Sun — about 150 million kilometers (93 million miles).

Most of the exoplanets discovered so far orbit closer to their stars than Earth — at less than 1 AU. These close-in planets are easier to detect with current methods like the transit and radial velocity. However, many of them are too hot or receive too much radiation to support life as we know it. Some orbit so close to their stars that they become tidally locked, meaning one side always faces the star while the other remains in darkness.

Astronomers also calculate a star's habitable zone — the range of distances where conditions might allow liquid water to exist on a planet’s surface. A planet within this zone is more likely to have temperatures suitable for life. The size and location of the habitable zone depend on the star’s temperature and brightness.