How doe one determine the temperatures of the other planets of our solar system?

In the case of Mars and Venus, there've been probes landed on the surface; I remember reading about the 'forecast on Mars' via the Viking landers "with over-night lows into the negative 100's..."

For the other planets, how much heat they receive from the sun can be calculated by how far they are, and we can detect the amount of thermal radiation they emit from orbiting infrared satellites, giving us an idea of how cold/hot they actually are. Jupiter actually emits more heat than it receives from the sun, indicating that it generates thermal energy within all that mass.

Thermal radiation. The hotter an object is, the more thermal radiation it emits. This is usually in the infrared range but can be in other parts of the electromagnetic spectrum.

Wiki each one