With sapphire waterfalls, lava rain and orbits around dead stars, these distant worlds push the limits of what’s possible.

Sedna is drifting into a part of its path where human technology can finally contemplate catching up, and that window will ...

For the first time since Pluto was demoted, the idea of a true ninth planet is edging from speculation toward something ...

The newly identified cluster of Kuiper Belt objects lies about 4 billion miles from the Sun, offering fresh clues about how ...