The debate over Pluto’s planetary status has been ongoing since its reclassification as a “dwarf planet” in 2006 by the ...

Astronomers propose a new hypothetical planet, Planet Y, beyond Neptune, based on observed orbital anomalies in the Kuiper ...

A new study suggests the existence of Planet Y. This hidden planet may be affecting the Kuiper Belt. The gravity of Planet Y ...

After a decade of research, the discovery of a second dwarflike planet beyond Pluto was announced this week. For now, the planet is named 2012 VP113 after Vice President Joe Biden.

Pluto follows a path with an angle 17 degrees above the plane of the solar system's planets. This bizarre and distant Earth-like planet, though, isn’t the first hidden world to be proposed.

In fact, icy moons and dwarf planets in the outer Solar System appear to have liquid oceans below layers of thick ice. Recent research suggests there could even be oceans inside bodies beyond Pluto.

Based on the third requirement, the committee declared that Pluto no longer qualified as a planet because of its position in the cluttered Kuiper Belt, where thousands of objects sit beyond the ...

Out beyond Pluto, a large, massive world has been found that may be our Solar System's newest dwarf planet. But its large eccentricity might mean something more.

Pluto was now a double planet: Pluto itself measures about 1,485 miles (2,390 kilometers) across, Charon some 700 miles (1,127 km) across. Like Earth’s Moon, Charon has a large diameter relative ...

The hidden world -- thought to be much bigger than Pluto based on the model -- could explain unusual features of the Kuiper Belt, a region of space beyond Neptune littered with icy and rocky bodies.

It's a little pink ball of ice that's far beyond Pluto. There's a framed photo of the dwarf planet hanging on the wall of Sheppard's office; if he has his way, there soon will be more photos up there.

There might be a 9th planet even larger than Earth out beyond the orbit of Pluto. But there probably isn't, and here's why.