Daniel Whitmire, a retired astrophysics professor, believes that the mysterious Planet X (sometimes known as Planet Nine) has caused extinction-level events on Earth and will do so again. Even more frightening is the idea that it could happen at any time. Who is Whitmire and what exactly did he say?

Here’s what you need to know.

1. Whitmire Believes a Distant Planet Causes Mass Extinctions on Earth And Could Do So Again

Whitmire published findings earlier this year connecting the undiscovered Planet X to mass extinctions on Earth, according to Phys.org. The research was published in the Monthly Notices of the Royal Astronomical Society. The theory is that an undiscovered planet triggers comet showers that are tied to multiple mass extinction events in Earth’s history. Every 27 million years, this planet passes through a distant Kuiper belt of comets, knocking comets into our solar system. These comets then smash into the Earth and, the ones that don’t, disintegrate as they get near the sun, blocking some sunlight from reaching our planet.

Whitmire first published research on the idea of connecting Planet X to mass extinctions in 1985 in the journal Nature. He and colleague John Matese published the idea while working as astrophysicists with the University of Louisiana at Lafayette. Their research was even published on the cover of Time. The title of the then-shocking article was: “Did Comets Kill the Dinosaurs? A Bold New Theory About Mass Extinctions.” His theory is supported by a fossil record that points to comet showers happening every 26 to 27 million years.

2. Orbital Anomalies in a Comet Belt Indicate the Presence of an Unknown, Large Planet

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Whitmire’s theory got a boost earlier this year when Caltch researchers found orbital anomalies in the Kuiper Belt, which Whitmire proposes is the source of the mass extinction comet showers. The anomaly points to the presence of an undiscovered large planet that is 10 times the mass of the Earth and also 1,000 times more distant from the sun.

Mike Brown and Konstantin Batygin, both from Caltech, analyzed the motion of a group of small objects in the outer parts of our solar system and found that an unseen body must be influencing them — likely a massive planet. The objects are clustered in the Kuiper Belt, far, far away from Earth. The Kuiper Belt is beyond Neptune, a field of icy objects and debris.

OK, OK, I am now willing to admit: I DO believe that the solar system has nine planets. — Mike Brown (@plutokiller) January 20, 2016

The evidence was published in The Astronomical Journal. You can read the study at this link. According to the study, the unusual orbits of the objects in the Kuiper Belt can be accounted for by a massive planet whose orbit is in the same plane. Planet Nine is estimated to have a mass that’s about 10 times that of Earth and an orbit that is 20 times farther from the sun on average than Neptune’s, according to Caltech.

3. But Some Scientists Say Planet Nine is Not the Same as Whitmire’s Planet X

Brown doesn’t think Whitmire’s planet matches the Planet Nine that he’s seeing evidence for.

“Whitmire has been speculating for decades about a very distant very massive planet pushing comets around. It has to have an orbital period of something like 27 million years,” Brown said to Discovery. “…It definitely has nothing to do with Planet Nine, which is much closer to the Sun and thus ‘only’ takes 15,000 years to go around.”

He said the evidence for Planet Nine says nothing about whether Planet X could or could not exist.

However, Whitmire has said that although he knows the current evidence for Planet Nine doesn’t fit his Planet X ideas, precisely, he’s still enthusiasitc about the connection, Metro reported.

“I feel very positive about the new evidence though the current estimates are not completely consistent with our Planet X model.” He added that it is possible that a smaller, closer planet could explain the Kuiper belt anomalies.

4. Whitmire Is a Retired Astrophysics Professor, Currently Teaching Math at the University of Arkanasas

Es aproximadamente 4 veces mayor q Júpiter. (John J. Matese and Daniel P. Whitmire – Cornell University 4 -26- 2010) pic.twitter.com/j82UTYyN6N — Daniel G. Urbina M. (@DanielUrbina56) March 19, 2015

Whitmire is retired from the University of Louisiana at Lafayette. He retired in 2012. In 2013, he began teaching math at the University of Arkansas.

Whitmire’s Rate My Professor rating at Arkansas is varied. Some students complained that he wasn’t familiar with current tech like Blackboard. Others said he is a great professor, easy to talk to, and always willing to lend extra help if needed.

5. Planet X and Planet Nine Are Tied to End-of-the-World Mythology

The idea of a planet causing worldwide destruction is also tied to mythology and doomsday predictions. A number of myths and conspiracy theories exist that a mysterious ninth planet lurks out in the shadows of our solar system and is responsible for hurtling asteroids toward Earth and causing past extinction events. This mysterious planet has been called by many names, from Planet X to Nibiru and more.

One doomsday theory is about Nemesis, a companion star to our sun, or a gas giant that may have a planet that orbits it. The general theory is that Nemesis is tied to extinction events on Earth. The idea was first presented in 1984 by scientists from the University of California in Berkeley and Princeton University, according to an AP story published at that time. They believed a dim dwarf star might periodically cause immense comet showers that killed up to 70 percent of life on Earth.

There have also been many claims that the ancient Sumerians somehow knew about an extra planet that was beyond Pluto in our solar system. They site photos, such as the one above, as evidence that the Sumerians knew of an extra planet. The photo is of an image on an ancient Sumerian cylinder seal showing planets orbiting the sun, which some say includes an extra, mysterious planet. Zechariah Sitchin, labeled a “pseudo-scientist,” claims in his books that this is an example of Sumerians’ knowledge of a cataclysmic planet.

There’s also the Nibiru myth, which is the idea that a large planet will come close to or collide with Earth in the 21st century and create a doomsday event. The planet is typically called Nibiru or Planet X. Scientists reject the theory. It was first proposed by Nancy Lieder in 1995.