Beyond Neptune lies the Kuiper Belt, a vast expanse of icy bodies that may hold clues to the solar system’s formation. These ...

Scientists work to define a “habitable zone,” which means that if it’s too close to a star, the water heats and evaporates, and too far, it freezes. Also, the atmospheric conditions need to be just ...

The number of planets that orbit the sun depends on what you mean by “planet,” and that’s not so easy to define ...