Two years ago, two Caltech Professors -- Konstantin Batygin and Mike Brown -- kicked the news media into high gear by predicting the existence of Planet Nine, a new, but as-yet unseen planet in the outer solar system. Their trans-Neptunian world has an orbital period of about 20,000 years, and a super-Earth mass more than sufficient to bring the planet count back up to nine.
Batygin and Brown's paper, has been downloaded more than half a million times, and presents indirect dynamical evidence for Planet Nine. Its presence is inferred through the gravitational sculpting that it has produced in the trajectories of the most distant Pluto-like worlds that lie beyond Neptune's orbit.
Follow-up papers by a range of authors have added a mixture of credibility, detail, and skepticism to the Planet Nine hypothesis. During the past two years, Planet Nine has been invoked as an explanation for the generation of highly inclined Kuiper belt objects such as Drac and Niku, it has been shown that it can account for curious orbital commensurabilities among the most distant members of the Kuipier Belt, and it has been hypothesized that it can explain the 6-degree tilt of the planetary orbits relative to the Sun's equator. If it does exist, the most likely sky location for Planet Nine is roughly RA=2h, Dec=0 deg, near aphelion (although the uncertainty on this direction is substantial). The favored area of the sky is optimally visible during late autumn for a planet at opposition. At the most probable current location, the planet's current distance would be r~950 AU, and the expected V magnitude is 22.4. A number of groups have engaged in the hunt, and there is something of an emerging consensus that if the planet exists to be found, it'll be found sooner rather than later. As an example, Mike Brown gave sixteen months fifteen months ago. This fourth update to our original, now closed, Planet Nine question is thus in order:
Will the discovery by direct observation of a new solar system planet having characteristics substantially similar to those described in the Batygin-Brown paper, be announced in a peer-reviewed paper prior to July 1, 2019?
(For this question to resolve as "Yes", the new solar system planet should have an inferred radius larger than that of Earth, an orbital period greater than 5,000 years, and an orbital eccentricity e > 0.25).