Why is earth sometimes called a goldilocks planet?

The term comes from the story of Goldilocks and the Three Bears in which she first tried porridge that was to hot, then too cold, then just the right temperature. Similarly, Earth is the right temperature to support life as we know it. All other other planets in the solar system and most planets in other solar systems are either too hot or too cold.

Because the conditions are "just right" - not too hot and not too cold.

From the Goldilocks and the three bears story.

See related question.

Because it is located in an orbit aorund our Sun that gives it the right temperature for liquid water and things to grow. It is not too hot and not to cold. Just right.

Of all the planets in our Solar System, only Earth has known life on it. That's because our planet orbits in what scientists call the Goldilocks Zone-the distance from the sun that creates temperatures that are not too hot or too cold to support life. The Earth has a breathable atmosphere, too. Everything is "just right." Scientists are looking around the galaxy for other planets in this zone-we might not be alone!