A powerful new tool comes online this year that could help astronomers locate the mysterious planet hiding somewhere beyond ...

The way people think of the Solar System has changed many times throughout history. Before the development of the telescope, these ideas were based on what could be seen with the naked eye.

The potential discovery of a large planet beyond Neptune’s orbit could change everything we know about the Solar System.

There may be an undiscovered planet in the outer solar system whose presence is revealed by the strange orbit of objects beyond the eighth planet Neptune. The tantalizing prospect of a ninth ...