Periodic mass extinctions on Earth, reflected in the global fossil record, could be linked to a possible ninth planet, according to a study published by a member of the Department of Mathematical Sciences at the University of Arkansas. Daniel Whitmire, a retired professor of astrophysics, is currently an instructor in mathematics. He published a paper in which he pointed out that the as-yet-undetected "Planet X" could cause comet showers associated with mass extinctions on Earth at intervals of about 27 million years.
Although scientists have been looking for a ninth (and sometimes tenth) planet for a hundred years, the possibility of its existence has been particularly highlighted recently, when scientists at the California Institute of Technology have suggested its existence based on orbital anomalies of objects in the Kuiper belt, a disk-shaped region inhabited by comets and other large bodies outside of Neptune. If Caltech scientists are not wrong, the ninth planet should be 10 times heavier than Earth and 1000 times farther from the Sun.
Whitmire and his colleague John Matese first published a study of the link between an unknown planet and mass extinctions in Nature in 1985 while working as astrophysicists at the University of Louisiana at Lafayette. Their work appeared on the cover of Time magazine in 1985 with a loud headline: “Did comets kill dinosaurs? A bold new theory of mass extinctions."
At that time, there were three explanations that could explain the regular streams of comets: Planet X, the existence of a sister star of the Sun and vertical oscillations of the Sun as it orbital wander through the galaxy. The latter two ideas were subsequently ruled out as irrelevant to the fossil record. Only planet X remained a viable theory, and now interest in it has flared up many times.
Whitmire and Matese's theory is that as planet X rotates around the sun, its tilted orbit rotates slowly and planet X passes through the Kuiper belt with comets every 27 million years, pushing comets into the inner solar system. The downed comets not only crash into the Earth, but also disintegrate in the inner solar system, as approaching the Sun reduces the amount of sunlight reaching the Earth.
In 1984, a study of paleontological records supported the idea of regular cometary streams over 250 million years. New research extends this period to 500 million years.
Whitmire and Matese published their own estimates of the size and orbit of planet X in the original study. They believe that the planet should be between one and five Earth masses and 100 times farther from the Sun, which is much less than the estimates of the Caltech scientists. Matese has since retired and has never been published again. Whitmire left the University of Louisiana at Lafayette in 2012 and began teaching at the University of Arkansas in 2013.
He says that it is especially interesting that a distant planet could seriously affect the evolution of life on Earth.
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