Planet Nine Hypothesis Takes a Major Hit in New Study

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It used to be easy to know how many planets there were: nine. It had been nine planets for an entire generation before scientists started rethinking what counts as a planet. Pluto is out, but some astronomers believe there’s a real ninth planet lurking out there. Others aren’t convinced, and the debate is starting to shift in favor of the planet nine skeptics. 

To be clear, there have been crackpots who, at various times, have claimed that a tenth (or ninth) planet was going to collide with Earth. The scientific debate over Planet Nine focuses on a 2016 study penned by astronomers Michael Brown and Konstantin Batygin. In it, the pair shows how the unusual orbits of numerous extreme trans-Neptunian objects (ETNO) could be the result of a massive, undiscovered object in the outer solar system. 

Other scientists were understandably skeptical of these claims, but the evidence presented by Brown and Batygin wasn’t as easy to dismiss as conspiracy theories about Planet X. The orbits cited in the study are odd, and they do support the idea there’s a massive something out there. We don’t know it’s a planet, though, and the math suggests it should be substantially larger than Earth. So where is it?! Some scientists have speculated that Planet Nine may actually be a small black hole — after all, the only evidence we have for Planet Nine is gravity. 

A new pre-print study led by the University of Michigan’s Kevin Napier posits an alternative explanation. Perhaps, the team says, the supposed clustering of ETNO orbits in the outer solar system is an illusion caused by biased data. According to Napier, it’s very hard to spot the tiny ETNOs at such great distances. So, astronomers have to adjust their telescopes to focus on specific parts of the sky, taking note of both the time of day and year. The result is allegedly an incomplete view of ETNOs. So, the clustering isn’t really clustering — those are just the objects Brown and Batygin happened to catalog. 

Planet Nine may be the cause of the clustering of ETNO orbits.

The team went a step further by checking in on 14 ETNOs that were not included in the initial Planet Nine paper. They found no indication these objects were being affected by the supposed Planet Nine. 

This study still needs to be peer-reviewed, but the team seems confident. Some of them are even out there talking smack on Twitter. Time will tell who’s right about this, but the Planet Nine supporters are going to need some new evidence to keep up the fight.

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