Astronomers find evidence of a possible ninth planet beyond Neptune, reigniting the debate about the formation of the Solar ...

If you were born in the last century you might have memorized that there were nine planets in ... the summer of 2006, Pluto was demoted. This wasn't the first time such a debate happened.

To everyone who was happy about Pluto's planetary demotion, consider this: If Earth rode the same orbital highway as Pluto, it too would be a dwarf planet. In fact, we live on a geological body ...

A new dwarf planet, discovered beyond Neptune and described as Pluto's 'cousin,' could void the hypothesis of a Planet X in ...

A small team led by Sihao Cheng, Martin A. and Helen Chooljian Member in the Institute for Advanced Study's School of Natural ...

Astronomers have announced the discovery of a new dwarf planet in our solar system, named 2017 OF201. Located far beyond ...

(Correction: An earlier version of this story misstated how far Pluto is from the sun. The correct number is 3.7 billion miles.) What was discovered in Flagstaff, Arizona, and killed off in Prague?

Pluto has become a beloved object in our solar system ever since the International Astronomical Union (IAU) reclassified it from a planet to a dwarf planet back in 2006 – a decision which has ...