Daniel Whitmire, a retired astrophysicist and current faculty member in the Department of Mathematical Sciences, will discuss his research on the relationship between the "Planet X" and periodic mass extinctions on Earth in a colloquium scheduled for 4 p.m. today, Friday, Feb. 24, in room 133 of the Physics Building.

Whitmire published findings in the January 2016 issue of Monthly Notices of the Royal Astronomical Society indicating the as-yet-undiscovered "Planet X" triggers comet showers linked to mass extinctions on Earth at intervals of approximately 27 million years.

Though scientists have been looking for Planet X for 100 years, the possibility that it's real got a big boost recently when researchers from Caltech inferred its existence based on orbital anomalies seen in objects in the Kuiper Belt, a disc-shaped region of comets and other larger bodies beyond Neptune. If the Caltech researchers are correct, Planet X is about 10 times the mass of Earth and could currently be up to 1,000 times more distant from the sun.

Whitmire and his colleague, John Matese, first published research on the connection between Planet X and mass extinctions in the journal Nature in 1985 while working as astrophysicists at the University of Louisiana at Lafayette. Their work was featured in a 1985 Time magazine cover story titled, "Did Comets Kill the Dinosaurs? A Bold New Theory About Mass Extinctions."

Whitmire and Matese's theory is that as Planet X orbits the sun, its tilted orbit slowly rotates and Planet X passes through the Kuiper belt of comets every 27 million years, knocking comets into the inner solar system. The dislodged comets not only smash into the Earth, they also disintegrate in the inner solar system as they get nearer to the sun, reducing the amount of sunlight that reaches the Earth.