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stormwyrm writes:

Ethan Siegel at Starts With A Bang brings to attention the results of the Outer Solar System Origins Survey (OSSOS). The OSSOS project, which started in 2013 (before the Planet Nine hypothesis was proposed) to survey the minor planets of the outer Solar System, has discovered and determined the orbits of well over eight hundred trans-Neptunian objects (TNOs) in its operation. They have recently published a paper that basically puts the kibosh on the Planet Nine hypothesis. Planet Nine was initially proposed to explain an apparent anomalous clustering of orbits of TNOs consistent with them being perturbed by a large planet, but the OSSOS results have found no such anomalous clustering, and are rather seeing a distribution consistent with uniform randomness.

From Forbes' Javascript-required article:

It was perhaps the most exciting idea to come out of science last year: that an undiscovered, giant world exists in our Solar System, far beyond the orbit of Neptune. This wouldn't be some tiny, frozen world like Pluto or Eris, smaller even than Earth's Moon, but a monstrous super-Earth, perhaps ten times as massive as our own world and almost as large as Uranus or Neptune in radius. As the months passed since it was first proposed by Konstantin Batygin and Mike Brown, they compiled additional evidence for it, and things were looking rosy. But a new study by Shankman et al. has turned the evidence on its head, disfavoring the planet's existence and uncovering a bias in the data itself.

[...] what they found was entirely consistent with no Planet Nine, and that the overall case for Planet Nine's existence was substantially weakened by their study. In particular, the clustering in the orientation of each orbit in space (defined by multiple variables, ω and Ω) that earlier studies, like Batygin & Brown and Trujillo & Sheppard, previously noticed simply doesn't exist in this new, unbiased study.

We find no evidence in the OSSOS sample for the ω clustering that was the impetus for the current additional planet hypothesis.

The data from this new study is quite clear that the previously observed correlation, which was the impetus for hypothesizing Planet Nine, doesn't persist into the new sample.

OSSOS also has a Frequently Asked Questions page about these findings. They don't entirely rule out the existence of a substantial (perhaps Mars-sized) planet in the outer reaches of the Solar System, but their data makes it highly improbable that a super-Earth on the scale of Uranus or Neptune might be out there.

Additional reading:
https://www.sciencemag.org/news/2017/06/new-haul-distant-worlds-casts-doubt-planet-nine

Original Submission

takyon writes:

Medieval astronomical records, such as the Bayeux Tapestry, could help narrow down the location (or at least infer the existence) of the hypothetical Planet Nine:

Scientists suspect the existence of Planet Nine because it would explain some of the gravitational forces at play in the Kuiper Belt, a stretch of icy bodies beyond Neptune. But no one has been able to detect the planet yet, though astronomers are scanning the skies for it with tools such as the Subaru Telescope on Hawaii's Mauna Kea volcano.

Medieval records could provide another tool, said Pedro Lacerda, a Queen's University astronomer and the other leader of the project.

"We can take the orbits of comets currently known and use a computer to calculate the times when those comets would be visible in the skies during the Middle Ages," Lacerda told Live Science. "The precise times depend on whether our computer simulations include Planet Nine. So, in simple terms, we can use the medieval comet sightings to check which computer simulations work best: the ones that include Planet Nine or the ones that do not."

Also at Queen's University Belfast.

Related: "Planet Nine" Might Explain the Solar System's Tilt
Planet Nine's Existence Disfavoured by New Data
Study of ETNOs Supports Planet Nine's Existence
Passing Star Influenced Comet Orbits in Our Solar System 70,000 Years Ago

Original Submission