From the coldest planets to spacecraft that have exited the Solar System, these little-known facts stump even many professional astronomers.

KEY TAKEAWAYS

Earth doesn’t have the most water in the Solar System, the farthest planet from the Sun isn’t the coldest, and the only planet made mostly of metal isn’t the densest.

Forget those shallow arguments about whether Pluto should be classified as a planet, and instead consider why non-planetary bodies that are actually larger than Mercury aren’t afforded more attention?

Very few people, even among professional astronomers, can answer all seven of these questions with factually correct answers. Are you one of the rare ones who can?