If the object really is Planet Nine, it would be larger than Neptune and exist 700 times further from the sun than Earth.

Science textbooks may be in for another revision. Our solar system shrank from nine planets to eight after the International ...

Our solar system may have a ninth planet after all, following the declassification of Pluto nearly two decades ago, ...

The presence of another planet in the solar system could explain the odd movements of some of the bodies in the Kuiper Belt.

Astronomers searching for a ninth planet in our solar system say they've found a "good" candidate far beyond Neptune, according to a new preprint study. This could be humanity's first glimpse at the ...

Astronomers have long speculated about an unseen planet lurking in the solar system's outer edge. This hypothetical world, dubbed Planet Nine, could explain the unusual clustering ...

The hunt for Planet Nine—the solar system’s ghostly gravitational troll—is longstanding, and is based on the peculiar clustering of rocky bodies in the Kuiper Belt beyond the orbit of Neptune.

This week, an old astronomical controversy is renewed as researchers present new evidence for a hidden "Planet X" in our ...

A ninth planet the size of Neptune may be hidden in the far reaches of the solar system, but the evidence has left some experts skeptical.

Scientists may have just spotted Planet Nine — a massive object orbiting 700 AU from the Sun. Data from two space telescopes ...