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Caltech astronomers, Konstantin Batygin and Mike Brown, proposed the presence of a new planet on the periphery of the solar system in 2016 to explain the complex orbital structure of the Kuiper Belt, a field of icy bodies gravitating around the Sun beyond Neptune. Since then, astronomers have been busy collecting evidence of its existence. Now, Batygin, Brown, and two University of Michigan astronomers, Juliette Becker and Fred Adams, have reviewed this evidence in two papers.
Artist's impression of the planet Nine. Image credit: Tom Ruen / ESO.
Planet Nine's hypothesis is based on evidence suggesting that the grouping of Kuiper Belt objects is influenced by the gravitational tugs of the invisible planet.
The question of whether this clustering actually exists or whether it is an artifact resulting from a bias in how and where objects of the Kuiper belt are observed is an open question.
To determine if the apparent cluster is at the origin of an observation bias, Professor Brown and Dr. Batygin have developed a method to quantify the magnitude of bias in each individual observation and then calculated the probability that the clustering is parasitic.
The researchers found that this probability is about one in 500. The results were published in an article by Astronomical Journal.
"Although this analysis does not say anything directly about the presence of Planet Nine, it nonetheless indicates that the hypothesis rests on a solid foundation," said Professor Brown.
Orbits of the Kuiper Belt and the distant Nine Planet: the orbits in purple are mainly controlled by the gravity of the planet Nine and have a narrow orbital clustering; Green orbits, on the other hand, are strongly coupled to Neptune and have a wider orbital dispersion; The updated orbital calculations suggest that Planet Nine is a planet of 5 to 10 Earth mass that resides in a slightly eccentric orbit with a period of about 10,000 years. Image credit: James Tuttle Keane / Caltech.
The second article, published in the journal Physics reports, provides thousands of new computer models of the dynamic evolution of the remote solar system and offers an updated overview of the nature of Planet Nine, including an estimate that it is smaller and closer to the sun than it is. we did not think so before.
On the basis of the new models, Dr. Batygin and Professor Brown – as well as Becker and Professor Adams – concluded that Planet Nine had a mass between 5 and 10 times that of Earth and an orbital semi-major axis in the vicinity of 400 AU smaller and closer to the Sun than previously thought – and potentially brighter.
"With five land masses, the planet Nine will probably look a lot like a typical extrasolar super-Earth," said Dr. Batygin.
"This is the missing link in the solar system for the formation of the planet. Over the past decade, investigations of exoplanets have revealed that planets of similar size were very common around other Sun-like stars. Planet Nine will be the closest thing we can find in a window on the properties of a typical planet in our galaxy. "
"The strongest argument in favor of Planet Nine is that independent data sources can all be explained by a proposed new planet having the same properties," said Professor Adams.
"In other words, there are many reasons to believe that Planet Nine is real, not just one."
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Michael E. Brown and Konstantin Batygin. 2019. Orbital grouping in the remote solar system. A J 157, 62; doi: 10.3847 / 1538-3881 / aaf051
Konstantin Batygin et al. The hypothesis of the new planet. Physics reports, published online February 10, 2019; doi: 10.1016 / j.physrep.2019.01.009
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