Beyond Neptune, a celestial object puzzles astronomers with its synchronized motion with the giant planet. Its inclined orbit ...

Is there a massive undiscovered planet on the outer reaches of the solar system? The idea has been around since before the ...

An icy object in perfect sync with Neptune reveals new details about planetary migration and unseen bodies far beyond the Kuiper Belt.

Early observations of the planets revealed worlds far different from Earth, demonstrating that the universe was far more ...

The celestial body's unusual orbit “implies that something extraordinary occurred" in the early days of the solar system—and ...

Astronomers have discovered "Ammonite," a mysterious object on the solar system’s edge whose unusual orbit challenges current ...

Typically, telescopes are synonymous with bringing far-off objects close, but the newest member of the solar system was ...

Theories about Planet Nine have been swirling for years, but this newly discovery planet might put those theories to bed for good.

In the dark, icy outskirts of our solar system—far beyond Neptune's orbit—astronomers have discovered a cosmic oddball that ...

A newly found icy object, Ammonite, may be a 4-billion-year-old fossil from the Solar System’s edge—and it’s casting doubt on the Planet Nine theory.