Why is Neptune the coldest planet, even though it has stars close to it?

Neptune is the coldest planet within our Solar System because it is the furthest planet from the Sun.

The Sun is the ultimate source of energy for the Solar System. The temperature of a planet is affected by its distance from the Sun. Radiation from the Sun is lost to its surroundings as it travels through space. Thus, the closer a planet it is to the Sun, the warmer the planet is likely to be. Likewise, the further a planet is from the Sun, the cooler the planet is likely to be. This trend holds true for all planets except Venus.

Starting from the center of the Solar System that is closest to the Sun, the order of the planets is: Mars, Venus, Earth, Jupiter, Saturn, Uranus, and Neptune. The saying “my very educated mother just served us nachos” is often used to remember this order of the planets. Again, since Neptune is the furthest planet from the Sun, it is also the coldest.