New evidence suggests a ninth planet lurking at the edge of the solar system

Astronomers at the California Institute of Technology announced Wednesday that they have found new evidence of a giant icy planet lurking in the darkness of our solar system far beyond the orbit of Pluto. They are calling it "Planet Nine." Their paper, published in the Astronomical Journal, estimates the planet's mass as five to 10 times that of the Earth. But the authors, astronomers Michael Brown and Konstantin Batygin, have not observed the planet directly. NASA's director of planetary science, Jim Green, cautioned Wednesday that there could be other explanations for the observed motion of the small bodies in the outer solar system. He referenced the famous dictum from Carl Sagan that "extraordinary claims require extraordinary evidence. The Sagan Rule applies. If it's there, find it. I challenge you. Somebody out there oughta find it," Green said.