PDF link: <a href="https://arxiv.org/pdf/1902.10103" rel="nofollow">https://arxiv.org/pdf/1902.10103</a><p>From the abstract, "This paper reviews the observational motivation, dynamical constraints, and prospects for detection of this proposed object known as Planet Nine".<p>I decided to share this paper from M. Brown and K. Batygin as I know there are many, on HN, interested about Planet Nine, and this paper seems to be a great review from the authors of the original paper itself. For users interested in shorter posts, I recommend checking out Batygin's posts from findplanetnine.com