Planet temperature

The temperature of a planet depends mostly on how much energy it receives from its star. This is influenced by the planet’s distance from the star, the star’s brightness, and the planet’s atmosphere, if it has one. A planet that orbits close to a hot star is usually much warmer than one farther away.

Astronomers often estimate a planet’s temperature using its orbital distance and the star’s luminosity. This calculation provides the equilibrium temperature — an estimate of how warm the planet would be without an atmosphere. However, the actual temperature can be higher or lower depending on factors like greenhouse effects, surface reflectivity (albedo), or geological activity.

In the Stellar Catalog, planet temperatures are displayed in both kelvins (K) and degrees Celsius (°C). For example, many hot exoplanets that orbit very close to their stars — such as ultra-short-period planets — can reach over 1,000 K (which is about 730 °C). Cooler planets farther from their stars may have freezing temperatures, well below 0 °C.

Temperature gives important clues about a planet’s habitability. Planets with surface temperatures of several hundred degrees Celsius are too hot to support life as we know it. Conditions suitable for life are more likely found within a temperature range that allows liquid water to exist.