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Astronomer who killed Pluto says he’s discovered a new planet to make up for it.

R. Hurt/California Institute of Technology

Astronomer Michael Brown famously helped demote Pluto a decade ago. Now, together with his colleague Konstantin Batygin at the California Institute of Technology, he may rewrite science textbooks once again. In a paper published in the Astronomical Journal, the pair say they have found evidence of a new planet lurking far beyond Pluto. They’re calling it Planet Nine.”

The new planet, if it does exist, would be ten times as massive as Earth. Brown and Batygin have not observed it directly. Instead they inferred its existence from the motion of dwarf planets and other small objects that seem to have been influenced by the “massive perturber.”

“My daughter, she’s still kind of mad about Pluto being demoted, even though she was barely born at that time,” Brown told The Washington Post. “She suggested a few years ago that she’d forgive me if I found a new planet. So I guess I’ve been working on this for her.”