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

When astronomers found a large world farther out than Pluto, it became one of the final nails in the coffin of our ninth ...

Pluto is a dwarf planet; humans declared it to be one in 2006 since it is so small. It has little “ice mountains” on the surface. Scientists think the inside is actually water. Pluto’s ...

Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more. For decades ...

On Feb. 18, the sun will make its official debut in mystical Pisces, setting the stage for introspection, surrender and spiritual growth. This is followed by a perplexing square between Mercury in ...

Charon is large in size relative to Pluto, and is locked in a tight orbit with the dwarf planet. A new simulation suggests how it ended up there. By Jonathan O’Callaghan Some 4.5 billion years ...

What’s unique about the separation is that Pluto and Charon still share the same orbit. This new discovery is helping researchers better understand how planets form and evolve, especially icy worlds.

Rachel Feltman: For Scientific American’s Science Quickly, I’m Rachel Feltman. Unless you’re really on the low end of our listener age bell curve, chances are you grew up learning about our ...