The outer planets of the solar system are swarmed by ice-wrapped moons. Some of these, such as Saturn's moon Enceladus, are ...

Astronomers recently detected a stray quasi-moon in our planet’s orbit, but it's hardly the first stowaway to hang out around ...

A new study has proposed the existence of Planet Y, an alternative Planet Nine candidate that is smaller and closer to Earth than the hypothetical Planet X, which astronomers have been hunting for ...

A strange tilt in the outer reaches of the Kuiper Belt has scientists wondering if the solar system is hiding another planet—a potential “Planet Y” that could soon join the family of known worlds. The ...

LONDON — 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 ...