Aside from the solar system once again having nine planets—which it had before Pluto’s demotion in 2006—the discovery of a distant Earth-mass planet would have profound implications for ...

The potential discovery of a large planet beyond Neptune’s orbit could change everything we know about the Solar System.

Astronomers are on the hunt for a mysterious ninth planet, known as Planet Nine, which could change our understanding of the solar system. Is this hidden world real, or just a myth?

A powerful new tool comes online this year that could help astronomers locate the mysterious planet hiding somewhere beyond ...

The concept of Planet X, or Planet Nine, has captivated astronomers for decades. This hypothetical planet, theorized to be ...

A few decades ago, the Solar System had nine planets, but in 2006 the International Astronomical Union reclassified Pluto as ...

If Brown’s hidden world is real, Rubin will almost certainly find it or strong indirect evidence that it exists. “In the ...

Known as Planet Nine or Planet X, it is a hypothetical planet that has long been rumoured to exist in the outer solar system. Although "several claims to have found an extra planet have been made ...

The newcomer replacing Pluto presently goes by “Planet Nine.” If and when it finally shows up, it will get the honor of a ...