A New World's Extraordinary Orbit Points to Planet Nine (wired.com)

In early 2016, two planetary scientists declared that a ghost planet is hiding in the depths of the solar system, well beyond the orbit of Pluto. Their claim, which they made based on the curious orbits of distant icy worlds, quickly sparked a race to find this so-called Planet Nine -- a planet that is estimated to be about 10 times the mass of Earth. From a report: Now, astronomers are reporting that they have spotted another distant world -- perhaps as large as a dwarf planet -- whose orbit is so odd that it is likely to have been shepherded by Planet Nine. The object confirms a specific prediction made by Konstantin Batygin and Michael Brown, the astronomers at the California Institute of Technology who first argued for Planet Nine's existence. "It's not proof that Planet Nine exists," said David Gerdes, an astronomer at the University of Michigan and a co-author on the new paper. "But I would say the presence of an object like this in our solar system bolsters the case for Planet Nine."

Gerdes and his colleagues spotted the new object in data from the Dark Energy Survey, a project that probes the acceleration in the expansion of the universe by surveying a region well above the plane of the solar system. This makes it an unlikely tool for finding objects inside the solar system, since they mostly orbit within the plane. But that is exactly what makes the new object unique: Its orbit is tilted 54 degrees with respect to the plane of the solar system. It's something Gerdes did not expect to see. Batygin and Brown, however, predicted it. The rocky body is being described as 2015 BP519. Quanta magazine has more details.

Comments

9th planet = Pluto

[_Sharp'r_]

Yes, Pluto is still a planet.

Re:9th planet = Pluto

[knorthern knight]

This is not a recent development. Pluto's claim to planetary status has been doubtful since shortly after its discovery. Here's an article from 1934 http://blog.modernmechanix.com... that ends with the quote...
> So that Pluto ranks as the largest asteroid, rather than the smallest
> planet; and it may be necessary to look farther for unknown planets.

In a way, it's very similar to the story of Ceres. A pint-sized "planet" was discovered, and proclaimed to be a planet. Then another one, and another one, etc etc. Eventually it became ridiculous According to Wikipedia https://en.wikipedia.org/wiki/...
> As of 20 September 2013, the LINEAR system alone has discovered 138,393 asteroids.

Asteroids long ago stopped being called "planets".

Similarly, when Pluto was first discovered, it was called a "planet", but https://en.wikipedia.org/wiki/...
> In 1992, Albion was discovered, the first Kuiper belt object (KBO)
> since Pluto and Charon. Since its discovery, the number of known
> KBOs has increased to over a thousand, and more than 100,000
> KBOs over 100 km (62 mi) in diameter are thought to exist.

Again, you're looking at a gazillion "pint-size-planets" in similar orbits. You don't really expect kids to memorize a thousand plus planets in science class. And if you insist on forcing Pluto in, why not Eris https://en.wikipedia.org/wiki/... which is more massive than Pluto, even though Pluto is larger in size? And if you include Eris, then what about the slightly smaller ones like Quaoar and Sedna? And slightly smaller ones than them? You have to "draw a line in the sand" somewhere, or else you'll be calling every pea-sized fragement in orbit around the sun, a "planet".