The average temperature at Saturn’s cloud tops is about -178 degrees Celsius. Saturn has no solid surface, so this temperature refers to the upper visible atmosphere rather than land or a conventional ground level.
Saturn’s cloud tops are extremely cold because the planet is nearly 1.4 billion kilometres from the Sun. Sunlight is much weaker there than at Earth, and the visible clouds lie high in a hydrogen- and helium-rich atmosphere. The upper clouds contain ammonia ice, while deeper layers are expected to include ammonium hydrosulfide and water clouds under far greater pressure.
Saturn also emits more energy than it receives from sunlight. Heat left over from the planet’s formation, combined with slow gravitational compression, contributes to this internal energy. That is why Saturn’s atmospheric temperature cannot be explained by sunlight alone. The cloud-top value is an average: temperatures vary with altitude, latitude, season, and atmospheric weather systems.