Evidence suggests huge ninth planet exists past Pluto at solar system's edge

Astronomers investigating the odd alignment of rocks beyond Pluto have concluded that an undetected icy planet four times the size of Earth must exist

As science often does, it began with a "huh?" Some distant objects far beyond Pluto were behaving very oddly. The orbits of a handful of space rocks had aligned for no apparent reason. Though stumped at first, astronomers now have an explanation: a huge ninth planet at the edge of the solar system.

If the researchers have their sums right, the mysterious new world is 10 times more massive than Earth and up to four times the size. Nicknamed Planet Nine, it moves on an extremely elongated orbit, and takes a staggering 10,000 to 20,000 years to swing once around the sun.