Free Astronomy Magazine March-April 2016

PLANETOLOGY fully reproducing the orbital proper- ties of the consid- ered KBO sample. After computations lasting months, it emerged that the scenario more close- ly corresponding to the observational reality contempla- tes the existence of a planet with a mass between 10 and 15 Earth mas- ses (and a diameter from 2 to 4 times that of the Earth), located on a rather elongated orbit (ec- centricity of about 0.6), which brings it to a distance from the Sun from a min- imum of 200-300 AU to a maximum of 1200 AU (7 light-days), with period of rev- olution between 10,000 and 20,000 years. Contrary to what suggested by Trujillo and Sheppard, Batygin's models indicate that the orbit of the hypothetical planet would extend in the opposite direction to those of the KBOs that it keeps confined. The orbits of the latter would cross that of the planet, but without any risk of colli- sion, since orbital resonances (fixed rela- tionships between periods of revolution) would have over time been established, preventing the KBOs coming face to face with the planet. The overall orbital config- uration of the objects taken as sample would therefore be stable and governed by the gravitational influence of the hypo- thetical planet. The two Caltech researchers calculated that there is only one chance in about 15,000 that this clustering is emerging just by chance precisely in this period. All plane- tary orbits do, in fact, ro- tate very slowly around the Sun and their axes gradu- ally point in different di- rections. (It is the so-called “precession of the perihe- lion”, which for Earth has a period of about 112,000 years.) Without a dynamic mecha- nism hindering that move- ment, the ω values would not remain clustered for long. The numerical simu- lations of Batygin were T he two bril- liant re- searchers who re- proposed the ex- istence of a large trans-Neptunian planet: Mike Brown (left) and Konstantin Baty- gin. [Damian Do- varganes, Asso- ciated Press] In the side video, Brown and Baty- gin describe their point of view. [Caltech]