While the jury is still out on whether or not an undiscovered ninth planet is lurking on the outer edge of our Solar System, a new hypothesis suggests that this potential extra planet could be responsible for mass extinctions here on Earth - including the one that wiped out most of the dinosaurs.
Though Planet Nine has seen a resurgence in the media recently, researchers have actually been looking for a ninth planet in the Solar System for over 100 years. In fact, Daniel Whitmire, a maths instructor from the University of Arkansas, first published a paper in Nature on his own version of a ninth planet called Planet X, back in 1985, and has now suggested that the hypothetical planet could be responsible for catastrophic comet showers all the way over here on Earth.
So how does a planet that's hundreds of billions of kilometres away rain down death on Earth?
According to Whitmire's hypothesis, it's a rather simple process. Basically, Planet X orbits the Sun like everything else in the Solar System. But every 27 million years, he says, it passes through the Kuiper belt, and dislodges a bunch of comets that come flying toward the Sun. Earth gets caught in this crossfire and, bam, mass extinction.
Whitmire points to the fossil record, which shows some evidence that comet showers on Earth happen about every 26-27 million years. "In 1985, a look at the palaeontological record supported the idea of regular comet showers dating back 250 million years," the University of Arkansas explains. "Newer research shows evidence of such events dating as far back as 500 million years."
Not only would these comets hit Earth right in the face, they'd also burn up the closer they got to the Sun, therefore reducing the amount of light we receive.
Back in 1985, a bunch of researchers were trying to understand why mass extinctions happen, with three separate hypotheses leading the way: the existence of a ninth planet; the existence of a sister Sun; or the vertical oscillations of the Sun were to blame. Over the past three decades, the latter two hypotheses have been disproven, while the search for Planet Nine has only gained momentum.
Now, while the hypothesis makes sense on the face of things, we should point out that it has not been published, so it's more of a neat little concept that needs a whole lot of proper investigation. And, rather crucially, there is debate over how long the ninth planet's hypothetical orbit around the Sun actually is - which is at the very crux of Whitmire's argument.
As astronomer Mike Brown from the California Institute of Technology (Caltech), who is leading the new charge to find Planet Nine, told Discovery News, there's been debate over what the undiscovered, unproven ninth planet in our Solar System could actually be like.
Most significantly, while Whitmire's hypothetical Planet X has an orbit of 27 million years, the Planet Nine Brown and his colleagues are currently hunting down is much closer (relatively) to Earth, and has an orbit of 15,000 years.
"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 says. "While that idea may or may not make sense, 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."
"The evidence for Planet Nine says nothing about whether or not there is a more distant Planet X," he adds.
So before we can even begin to start blaming a ninth planet for our Earthly catastrophes, researchers actually need to prove its existence. But hopefully, as more and more institutions start searching for it, we will one day have definitive answer about the mysterious planet that may or may not be lingering just out of sight and ready to assault us with comets.
If supported by the evidence, Whitmire's hypothesis could provide a greater insight into how other planets in our Solar System affect evolution here on Earth.