A fresh study of the Kuiper Belt’s structure has revived that far-out question, pointing to a possible Earth-sized ...

The search for an unknown planet in our solar system has inspired astronomers for more than a century. Now, a recent study suggests a potential new candidate, which the paper’s authors have dubbed ...

On August 24, 2006, our solar system lost a planet. It wasn't by cataclysmic destruction, but rather by the vote of the International Astronomical Union, which declared that Pluto, considered the ...

If the solar system does have a Planet Nine, it is a world that was bullied by its larger siblings, exiled to the far reaches of space and only rescued from oblivion thanks to the intervention of ...

Our solar system now, once again, officially consists of only eight planets. Although largely debunked, speculation continued ...

A jealous Planet Nine may have shoved its siblings for attention. If a massive ninth planet exists in our solar system, it might explain why the planets are out of line with the sun. The eight major ...

A new study suggests yet another theory for a possible extra planet in our solar system, likely of a size between Mercury and ...