Earlier this year, scientists at Caltech offered the most convincing evidence yet of a ninth planet, Planet X. Now, a retired astrophysicist suggests the hidden planet is responsible for Earth’s periodic mass extinctions — like the disappearance of the dinosaurs. In a new study published in the journal Monthly Notices of the Royal Astronomical Society, Daniel Whitmire argues that an undiscovered ninth planet triggers disruptive comet showers every 27 million years.

It’s not the first time Whitmire — now a math teacher at the University of Arkansas — has made such a claim in a major scientific journal. In 1985, he offered a similar explanation for mass extinctions in the journal Nature — then an astrophysicist at the University of Louisiana at Lafayette. Whitmire and his research partner John Matese pointed to evidence of periodic comet showers in the fossil record dating back some 500 million years. FULL REPORT