Veritasium did a video about Planet 9 [1] with one of the authors of this article, Konstantin Batygin. It also features David Jewitt with opposing arguments regarding the existence of Planet 9.
That seems like the most interesting sci-fi plot explanation. Two alternative explanations for why we can find Planet 9 could be: it is a tiny, hard to see rock very far away, or it doesn’t exist.
I'm going to assume both of these options have been considered and ruled out. Also, the article mentions that this Planet 9 explains the orbits of Kuiper belt objects as well.
It's nice to see this again. The revelation that space is so big and empty is one that more people need to see. I especially recommend finding and visiting one of the scale models of the Solar System. I visited and walked the one in Melbourne, Australia.
They are referenced in previous discussions of this particular item. Here are some:
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