Astronomers Mike Brown and Konstantin Batygin post updates on their search for a hypothesized ninth planet in the outer solar system.
HN commenters recommend it as the place to follow the search and quote the authors on why the orbital clustering puzzled them.
I haven't seen the original research myself to judge, but it sounds like they're being careful about these effects. Looking at their discussion on the main page of http://www.findplanetnine.com/, the claim seems to be that this isn't "we spotted six out of the solar system's zillions of objects that formed a cluster" but rather "the unique six known objects within a certain range of orbital parameters all form a cluster in a different parameter".
More specifically, quoting from that page, "all Kuiper belt objects with orbits that do not veer into inter-planetary space and spend longer than approximately 2000 years to complete a single revolution around the Sun... trace out elliptical paths that point into approximately the same direction in physical space, and lie in approximately the same plane."
That could be just an observational coincidence, and that's where they claim the statistical figure that you've cited. I have no idea to what extent those figures account for the multiple comparisons issue, but the range of orbital parameters that I've quoted here doesn't look very fine-tuned to me. (The upper bound certainly isn't, anyway!) So it's just a question of how the lower bound was chosen. And on some level, I'm not even sure that that's an issue: an observation that's based on "the longest N bound orbits all show this pattern" feels meaningful to me even if I'm not sure in advance how big N is going to be.
The authors are not relying just on the improbability of that arrangement, but also on its stability. From one of the authors, on http://www.findplanetnine.com/:
"Mike and I were genuinely perplexed. Could the confinement of the orbits be due to an observational bias or a mere coincidence (after all, we are talking about six objects here - not exactly “big data”)? Thankfully, the probability of the observed alignment being fortuitous can be assessed in a statistically rigorous manner, and clocks in at right around 0.007%. Not a great gamble. Moreover, application of simple perturbation theory (or direct numerical integration) demonstrates that if allowed to evolve under the gravitational influence of Jupiter, Saturn, Uranus and Neptune, the orbits would become randomly oriented on timescales much shorter than than the multi-billion year lifetime of the solar system. So the dynamical origin of the peculiar structure of the Kuiper belt cannot be outsourced to the distant past - something is holding the orbits together right now."
Their site at http://www.findplanetnine.com/p/blog-page.html addresses the areas the Tyche survey and other surveys cover.
My TLDR:
* The WISE survey might only find Planet X at it's nearest approach. Kevin Luhman has redone the survey using the most sensitive WISE bands that only cover a narrow area of the sky and hasn't found Planet X.
* They reviewed the Catalina Sky Survey and eliminated most of the areas they'd expect Planet X.
* The Pan STARRS site survey didn't find Planet X.
Conclusion: Planet X is at aphelion, difficult to find with the Milky Way as a (stunning) backdrop.
I just found their paper: http://iopscience.iop.org/article/10.3847/0004-6256/151/2/22
I wonder how their conclusions match with David Nesvorny's paper predicting a 5th planet having been ejected from the Solar System: http://arxiv.org/pdf/1109.2949v1.pdf
I would love an update on efforts to find planet 9, unfortunately this article is from January 2016.
See [1] for a Hacker News thread from Jan on Planet 9, and [2] for a blog from Batygin and Brown.
[1] https://news.ycombinator.com/item?id=10939306https://news.ycombinator.com/item?id=10939306
[2] http://www.findplanetnine.com/
If this topic interests you, check out the really awesome lecture by one of the original paper authors. It's both informative and very well done.
https://www.youtube.com/watch?v=CMCwezegPNg
Forbes does mention the blog, and that's worth following directly too:
http://www.findplanetnine.com/
This article doesn't seem to contain much new. If you read Batygin and Brown's blog, though, you can read more about to what extent they've been able to pin down Planet Nine's location: http://www.findplanetnine.com/2017/09/planet-nine-where-are-you-part-1.html