He called this hypothetical world "Planet X." "In some ways, Pluto's more of a planet than some of the other established ...

Almost 10 years ago, a NASA spacecraft was able to take several photos of Pluto, known for decades as a planet before it was ...

A powerful new observatory is the best hope yet for finding the elusive Planet 9, a large planet that some scientists say is ...

Not fulfilling the second criteria, Pluto went from being the ninth planet in our solar system to one of five dwarf planets, with the IAU stating that Pluto is "an important proto-type of a new ...

Nevertheless, because it orbited the Sun like a planet, it was classified as a planet and named Pluto, after the god of outer darkness in Roman mythology. So things stood for 65 years. Although ...

The relative quantities of volatile gases like methane and ethane can reveal key details about distant Kuiper Belt objects.

Venus may be far more geologically alive than anyone expected. New research suggests its outer crust could be churning with convection, a process that helps move heat and may explain the planet’s tens ...