Researchers link mass extinctions to 'Planet X'
A study by retired astrophysics professor Daniel Whitmire linked mass extinctions on Earth to the undiscovered 'Planet X', which is believed to be the solar system's ninth planet living beyond Neptune. According to the theory, 'Planet X' passes through a belt of comets present beyond Neptune every 27 million years, hammering comets into the inner solar system, causing mass extinctions.