49th Meeting of the AAS DPS

So how has the evidence for the proposed Planet Nine held up over the course of the past year? The jury is still out, actually (though the opposing sides in the debate would probably be ready to argue that with me). At the 49th meeting of the AAS DPS (referred to as DPS49 from now on), leading solar system astronomers gathered after several months of back-and-forth debate. I want to highlight two especially notable talks at DPS49. The talks summarized two studies from Summer 2017 that reached completely opposite conclusions regarding the overall importance of observational bias on the observed grouping of distant TNOs. One, conducted by the Outer Solar System Origins Survey (OSSOS), concluded that the observed grouping is due entirely to observational bias. The other, conducted by Dr. Mike Brown (an original proposer of Planet Nine, together with Dr. Konstantin Batygin), concluded that the observed grouping cannot be explained by observational bias. Well now, that’s confusing. Does observational bias completely explain the observed grouping of the most distant TNOs, or does it not? The truth is that we don’t know (again, cue up the arguments by both sides of this debate). We simply don’t have enough data yet!

Further complicating the debate, a number of other studies examining additional possible evidence for or against Planet Nine (aside from the grouping of the most distant TNOs) were presented at DPS49. One particularly interesting study conducted by Juliette Becker of the University of Michigan analyzed the gravitational sculpting effects of Planet Nine on the most distant TNOs over timescales comparable to the age of the solar system. The study found that many of these objects would crash into the Sun or be ejected from the solar system completely if a solar system containing only the known planets is considered. How, then, are we able to observe them today with our telescopes? If Planet Nine is added to the solar system, it can actually help offset gravitational interactions that might otherwise lead to the unfortunate demise of the TNO. The help from Planet Nine would allow these objects to “live” longer in the solar system, such that they might still be around after 4.5 billion years (i.e. the present day) to be observed with our telescopes!

The glaring problem with the study I just described is that it assumes Planet Nine exists. But again, we still don’t know whether it exists! There is some hope, though -- the proposal of a new planet in the Solar System sent astronomers to telescopes around the world in a mad dash to find it. In the process of searching for Planet Nine, they have discovered several more extremely distant TNOs that would be affected by Planet Nine’s gravity, if Planet Nine exists. So while there is no new planet to report, additional discoveries of extremely distant TNOs are the next best thing!