Scientists have fiercely debated the existence of ‘Planet 9’ for a decade. Some say evidence is piling up

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Our solar system used to have nine planets. Astronomer Mike Brown, also known as “the man who killed Pluto,” said he got hate mail from kids and obscene calls at 3 a.m. for years after his most famous finding helped change that.

Brown, a professor of planetary astronomy at Caltech, discovered another small world called Eris in the Kuiper Belt — a vast ring of icy objects beyond Neptune’s orbit that also happens to be the former ninth planet’s neighborhood. The 2005 revelation set off a chain of events that led to Pluto’s still-controversial demotion from planet status the following year.

But now, just as the Kuiper Belt effectively took a ninth planet away, Brown and other scientists believe it could give one back.

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