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Corresponding with the three-year anniversary of their announcement hypothesizing the existence of a ninth planet in the solar system, Caltech's Mike Brown and Konstantin Batygin are publishing a pair of papers analyzing the evidence for Planet Nine's existence.
The papers offer new details about the suspected nature and location of the planet, which has been the subject of an intense international search ever since Batygin and Brown's 2016 announcement.
The first, titled "Orbital Clustering in the Distant Solar System," was published in The Astronomical Journal on January 22. The Planet Nine hypothesis is founded on evidence suggesting that the clustering of objects in the Kuiper Belt, a field of icy bodies that lies beyond Neptune, is influenced by the gravitational tugs of an unseen planet. It has been an open question as to whether that clustering is indeed occurring, or whether it is an artifact resulting from bias in how and where Kuiper Belt objects are observed.
To assess whether observational bias is behind the apparent clustering, Brown and Batygin developed a method to quantify the amount of bias in each individual observation, then calculated the probability that the clustering is spurious. That probability, they found, is around one in 500.
[...] The second paper is titled "The Planet Nine Hypothesis," and is an invited review that will be published in the next issue of Physics Reports. The paper provides thousands of new computer models of the dynamical evolution of the distant solar system and offers updated insight into the nature of Planet Nine, including an estimate that it is smaller and closer to the sun than previously suspected. Based on the new models, Batygin and Brown -- together with Fred Adams and Juliette Becker (BS '14) of the University of Michigan -- concluded that Planet Nine has a mass of about five times that of the earth and has an orbital semimajor axis in the neighborhood of 400 astronomical units (AU), making it smaller and closer to the sun than previously suspected -- and potentially brighter. Each astronomical unit is equivalent to the distance between the center of Earth and the center of the sun, or about 149.6 million kilometers.
-- submitted from IRC
The planet nine hypothesis (DOI: 10.1016/j.physrep.2019.01.009) (DX)
Orbital Clustering in the Distant Solar System (DOI: 10.3847/1538-3881/aaf051) (DX)
Previously: CU Boulder Researchers Say Collective Gravity, Not Planet Nine, Explains Orbits of Detached Objects
(Score: 4, Informative) by bzipitidoo on Saturday March 02 2019, @05:43AM
What definitions are the most useful? The distinctions between planet, dwarf planet, moon, and asteroid are to a large degree circumstantial and artificial.
Yes, I agree that from a standpoint of impartial objectivity, the timing of the most recent redefinition of planet was very poor. New Horizons was on the way to give us our first close view of Pluto. They could have and should have waited for that information. Clearly, other considerations were in play. Perhaps they wanted to generate publicity, and one of the best ways to do that is whip up some drama. The media would have loved it even more if the astronomers had gotten into a fist fight during their meeting. Another likely motive was to poke at the US. And what better way than to demote the only planet discovered by an American? Even better that it was done when an American probe was en route for the only look we are likely to have for decades. That appearance of petty spite was unworthy of scientists.
Another factor that causes controversy is the highly questionable criteria they adopted. People have somewhat gleefully pointed out serious problems, presenting situations in which the new definition does not work well. For instance, a body could change status between planet and moon once each orbit. Pluto and Charon are really a double planet, as their barycenter is in space, not within Pluto, yet everyone calls Charon a moon of Pluto. If Charon was in a highly elliptic orbit, the barycenter would move in and out of Pluto as Charon approached and then receded from perigee with Pluto. Even our own moon will eventually change status into a planet, when it has receded far enough to move the barycenter outside Earth. One of the big problems with gravitational dominance is that the further a body is from the star it orbits, the more massive it has to be to qualify as a planet.