Planet 9 hypothesis gets a boost (earthsky.org)

[eppur_se_muova]

By Paul Scott Anderson in Space | March 3, 2019

Does a large Planet 9 – a hypothesized planet several times the mass of Earth in the distant outer reaches of the solar system – really exist? That question is still a topic of heated debate among astronomers. Some think a large Planet 9 can explain the weird orbits of some of the smaller known bodies in the Kuiper Belt. Others think that those orbits might be caused by multiple unknown smaller bodies instead.

Several astronomers recently reviewed the evidence for Planet 9 in an article published in February 2019 by Physics Reports. This peer-reviewed journal aims to publish long and deep reviews – more extensive than just literature surveys – on timely topics in physics. The article is called The planet nine hypothesis, and the astronomers who wrote it are still very optimistic that Planet 9 will eventually be found and confirmed. According to co-author Fred Adams at the University of Michigan:

The strongest argument in favor of Planet 9 is that independent lines of evidence can all be explained by a proposed new planet with the same properties. In other words, there are multiple reasons to believe that Planet 9 is real, not just one.

From the review article in Physics Reports:

Over the course of the past two decades, observational surveys have unveiled the intricate orbital structure of the Kuiper Belt, a field of icy bodies orbiting the sun beyond Neptune. In addition to a host of readily-predictable orbital behavior, the emerging census of trans-Neptunian objects displays dynamical phenomena that cannot be accounted for by interactions with the known eight-planet solar system alone.

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more: https://earthsky.org/space/review-paper-physics-reports-planet-9-feb-2019
https://www.sciencedirect.com/science/article/abs/pii/S037015731930047X (free abstract, full article behind paywall)