This video explains why planets in our solar system orbit in nearly the same plane, tracing their origins back to a rotating ...

Is there a massive undiscovered planet on the outer reaches of the solar system? The idea has been around since before the discovery of Pluto in the 1930s. Labeled as planet X, prominent astronomers ...

A new study suggests yet another theory for a possible extra planet in our solar system, likely of a size between Mercury and ...

Our solar system is a smashing success. A new study suggests that from its earliest period—even before the last of its ...