* Distance from the Sun: The closer a planet is to the Sun, the more solar radiation it receives and the hotter it gets. This is why Mercury, the closest planet, is extremely hot, while Neptune, the farthest, is incredibly cold.

* Atmospheric Composition: Planets with thick atmospheres can trap heat from the Sun through the greenhouse effect. Venus, for example, has a thick atmosphere of carbon dioxide that makes it incredibly hot, even though it's farther from the Sun than Mercury.

* Rotation and Axial Tilt: A planet's rotation and axial tilt affect how solar radiation is distributed across its surface. This can lead to significant temperature variations between different regions. For example, Earth's tilted axis causes seasons.

* Internal Heat: Some planets, like Jupiter and Saturn, generate significant internal heat due to their gravitational pull and composition. This heat can contribute to their overall temperature, even if they are far from the Sun.

So, while the Sun is the primary source of heat for most planets, the amount of heat they receive and their overall temperature is influenced by a combination of factors.