A distant planet may lurk far beyond Neptune
![An artist's illustration of Planet X](https://www.sciencenews.org/sites/default/files/styles/article-main-image-large/public/main/articles/planetx_feat_free.jpg?itok=ZqQ_VQBV)
Out beyond Neptune, the solar system resembles the deep ocean: dark, remote and largely unexplored. To an Earth-bound observer, even the brightest objects, such as Pluto, are 4,000 times as faint as what the human eye can see. An undiscovered planet could easily lurk out there unnoticed, a possible fo
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