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Searching For Planet X; New Podcast Features Astrophysicist Daniel Whitmire

Short Talks From The Hill, a podcast from the University of Arkansas, highlights research and scholarly work across the campus. Each segment features a university researcher discussing his or her work.

Bob Whitby: Hello and welcome to Short Talks from the Hill a podcast from the University of Arkansas. my name is Bob Whitby, a science writer at the university. On this episode, Daniel Whitmire, an instructor in the mathematics department and a retired astrophysicist, discusses his research on Planet X and his theory of how it causes mass extinctions. Thanks for joining us.

Daniel Whitmire: Sure, my pleasure.

BW: Daniel, can you tell us a little bit about what Planet X is?

DW: Planet X in general has a long history, over a hundred years, people proposing an unknown planet in addition to the known planets for various reasons. Our Planet X model is specific to an explanation for periodic mass extinctions like the one that wiped out the dinosaurs, the dinosaurs and three-fourths of all species, that occurred about 66 million years ago. There are other mass extinctions, and according to some paleontologists, these mass extinctions are not random but they occur at a regular rhythm of 27 million years. So the Planet X. Our Planet X model, with my collaborator John Matisse, was proposed in 1985 in order to explain the evidence for the periodic mass extinctions. Recently there’s been more evidence for the periodic mass extinction, so our model has come back en vogue, and I published a paper about a year ago updating the model with the new evidence from paleontology.

Daniel Whitmire

BW: How does it work? How does Planet X cause mass extinctions?

DW: Well, it causes… We took our cue from the dinosaur extinction that was known to have been caused by impact of a comet or asteroid in the Yucatan Peninsula. So in order to explain Period, explain how mass extinctions could be periodic, we needed a mechanism to cause impacts on the Earth every 27 million years. So in the Planet X model the orbit of Planet X rotates through a disk of comets that lies beyond Neptune called the Kuiper Belt of comets. So the orbital period of Planet X is only about a thousand years. It’s located about three times farther out than Neptune, but the entire orbit itself rotates slowly and makes a complete revolution every 54 million years. Well, twice during that 54-million-year period it passes through the belt of comets, the Kuiper belt of comets, scattering comets, gravitationally effecting comets, and after all the dust settles, some of the comets have orbits that bring them into the inner solar system. So it produces what’s called a comet shower every 27 million years.

BW: And the comets hit the Earth?

DW: They hit the Earth and that’s one mechanism. That’s certainly what happened with the dinosaur extinction, but in addition to that the comets, especially the larger comets can break up as they orbit close. Some of them have orbits taking them close to the Sun. They break up, produce a lot of dust in the inner solar system and so the dusk and block sunlight. So that’s an additional environmental effect that could also contribute to the mass extinction events.

BW: And this theory is consistent with the record that they’re finding, the paleontological record?

DW: Yes, very much so.

BW: And it lines up with the 26 to 27 million year time periods?

DW: Correct. The reason the orbit of Planet X rotates with a period of 54, twice the extinction period… The reason it does that is because of the gravitational effect of the known planets. So given that it’s out there it’s got no choice; it has to rotate. Now the model depends on the orbit being out of the plane of the comets and the planets. The comets are in the same plane as the planets and so the orbit of this planet, Planet X has to be, for the theory to work, it has to be tilted. That’s, to visual eyes, imagine it’s tilted at 90 degrees, but it doesn’t have to be 90 degrees. It could be something more like 30 to 45 degrees.

Short Talks From The Hill features research and scholarly work across campus. Each segment features a university researcher discussing his or her work.

BW: Your theory is Planet X, but there’s also another theory out there called Planet 9.

DW: That’s correct.

BW: Which was recently in the news for being a ninth planet, Pluto no longer being a planet, so this would be the ninth planet. How is your theory different?

DW: My theory, the Planet X theory, is a smaller planet and it’s closer. So, the Planet 9 is out much farther, seven times farther than the Planet X theory, and it’s also much more massive. The mass of the Planet 9, the predicted mass, of course it hasn’t been discovered yet, but the predicted mass is about ten Earth masses, and ours is one to five earth mass so it’s less massive, and it’s also closer. Our planet would be roughly 100 AU. An AU is the distance of the Earth from the Sun. Neptune is at 30 AU so ours is about three times farther out than Neptune. There’s the Planet 9 model, because the planets so much bigger has to be farther out, and it’s out at about 700 AU.

BW: Both of these are theories at this point. Neither of these planets have been discovered.

DW: That’s correct. And there’s good evidence for Planet 9, so I would say that most astronomers and the majority of astronomers believe that it’s there. So that’s not, the evidence for Planet 9 is based on the clustering together of the orbits of large bodies essentially big comets in the Kuiper belt region, so that clustering wouldn’t last over the age of the solar system unless there was something there causing it. So that kind of, that’s the evidence. So the evidence for Planet 9 has nothing to do with mass extinctions, and that evidence is very good.  Now in case, in addition to the mass extinction which was the original motivation for proposing our Planet X model, in addition to that, there’s a recent study from two astrophysicists at Harvard on the motion of Pluto. So they find evidence in the discrepancies in the motion of Pluto that can be explained not by Planet 9, but by a planet like our Planet X. So we do have some recent reason to be encouraged. So we’re not saying this is an addition to Planet 9. Planet 9 sort of stands alone, and Planet X stands alone. But to the extent that you have one planet out there like Planet 9, then it makes it a lot more plausible that there’s a second or even more planets out there. So but we’re not claiming it’s the same as Planet 9.

BW: If your theory proved to be true, what would be the ramifications? Where would we be on course for another mass extinction at some point?

DW: In 16 million years or so.

BW: So no need to worry right away.

DW: Not for us.

BW: There’s a long history of people looking for Planet X, Planet 9, planets beyond our solar system. Can you speak to that a little bit and how that’s controversial?

DW: There’s a cult out there that believes the end of the world is approaching due to a planet. They call it Nibiru, but sometimes they call it Planet X, and it gets confused with our stuff and they sometimes even cite our stuff. But of course our model is based on science and it’s speculative but at least it’s based on science and the prediction is although there could be massive extinction on the Earth, but it’s going to be in 16 million years if we’re correct. And not next April or whatever the latest prediction is. So there’s no connection between those people, and in a way it’s a sad situation because I get emails from people who are almost hysterical thinking the end of the world is coming. And they’ve seen my name someplace and they want me to confirm it, or tell them what’s going on and you know and of course I tell them it’s nothing, that there is no scientific basis for any of this, the conspiracy theories that they’re hearing out there. It’s not based on any science whatsoever. And so that’s why people… I mean it’s interesting. I guess if you didn’t have any, if you had some evidence… But there is no evidence for it. So everything they say that rogue planet can do violates you know all the known laws of physics as well as everything we know about the solar system. So they just assert it and unfortunately a lot of people are not critical in their thinking and believe it. But it has nothing to do with our science and the science either of Planet 9 or Planet X.

BW: Music for Short Talks from the hill was written and performed by Ben Harris, guitar instructor at the University of Arkansas. For more information and additional podcasts go to or, the home of research news at the University of Arkansas.

About The Author

A former newspaper reporter, Matt McGowan writes about research in the College of Engineering, Sam M. Walton College of Business, School of Law and other areas. He is the editor of Short Talks From the Hill, a podcast of the University of Arkansas. Reach him at 479-575-4246, or

The University Relations Science and Research Team

Camilla Shumaker
director of science and research communications

Matt McGowan
science and research writer

Robert Whitby
science and research writer

DeLani Bartlette
feature writer

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