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.

In 1985, there were two alternative theories for what might trigger major comet showers -- a sister star to the sun, vertical oscillations of the sun as it orbits around the center of the Milky Way. Those theories have since been discredited, while the Planet X theory has acquired legitimacy.

The Caltech study estimated Planet X to be approximately 10 times the mass of Earth, big enough to throw comets into the inner solar system as its oblong orbit sends it closer to the Kuiper Belt every 27 million years.

The Kuiper Belt is a ring-shaped region of comets and other larger bodies circling the solar system just beyond Neptune. Caltech researchers inferred the existence and path of a ninth planet by studying anomalies in the orbits of several major Kuiper Belt objects.

Whitmire suggests -- as they did in 1985 -- that a periodic invasion of comets results in violent collisions. Those that miss Earth disintegrate in the inner solar system and dim the sun's solar energy, cooling Earth.

Whitmire is hopeful additional evidence of Planet X can offer more answers about the evolution of the solar system and life on Earth.

"I've been part of this story for 30 years," he said in a news release. "If there is ever a final answer I'd love to write a book about it."