No one's actually seen this mysterious ninth planet, but a preprint published on arXiv has significantly narrowed the search field and explains that Planet Nine existing is still the researchers' preferred hypothesis.
While it may seem small, that trimming of space represents a trimming of potential objects that could be Planet Nine from 1.2 billion to 244 million, with researchers hesitant to trim the fat further. While searching for Planet Nine through this large data set remains a formidable task, we could find no additional filters that appeared to safely further reduce the data set, the preprint authors write. Any one of these cuts in the data has the possibility of removing real detections of Planet Nine. Our calibration method must by necessity take this possibility into account.
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