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 ...

Growing up, I was taught that there were nine planets in the solar system. That all changed in 2006, when the International Astronomical Union voted to demote Pluto's status to that of dwarf planet.

Planet X, also called Planet Nine, is a hypothetical planetary body seven times the mass of Earth lurking behind Pluto. If found, this gassy, icy beast some 155 billion miles away from the sun ...

Although Seeing in the Dark doesn't directly discuss Pluto, it does celebrate the joy of observing planets. Viewers who watch the show may wonder what happened to Pluto in 2006 and whether any of ...

The same year that Pluto was ignominiously stripped of its status, a paper was published theorizing that there was another planet, a very big planet, beyond Neptune. The Planet Nine theory was ...

Known as Planet Nine or Planet X, it is a hypothetical planet ... For more than 70 years, Pluto was classed as the ninth planet but that changed in 2006, when the International Astronomical ...

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 ...

Rumya Sundaram, Citizen Scientist Coordinator for the Key Biscayne Community Foundation, will present this month’s Citizen ...

Charon is half the size of Pluto, “making it the largest known moon relative to its parent planet in our solar system,” NASA notes. So how did Pluto get its chonky companion? A new study ...

NASA launched the New Horizons probe which would provide never-before-seen images of the dwarf planet, its moons and other objects.