Free Astronomy Magazine March-April 2016

PLANETOLOGY by a very wide orbit, comparable to that of the famous dwarf planet Sedna for the fact of having a perihelion very external to the orbits of major planets, such as not to be affected by the gravitational influence of Neptune, to which are instead subject a number of other Edgeworth-Kuiper belt objects (known as KBOs). 2012 VP 113 , Sedna and a handful of others similar to them are considered the brightest and closest mem- bers of a population of KBOs orbiting in the outer-belt regions. The discoverers of 2012 VP 113 , Chadwick Trujillo (Gemini Observatory) and Scott Sheppard (Carnegie Institution for Science), noticed immediately that the final orbit of the new object has in common with Sedna a very revealing parameter, the argument of perihelion ( ω ), whose value, close to 300 degrees indicates that both KBOs reach peri- helion and cross the ecliptic plane (south to north) on the same side with respect to the Sun. Intrigued by this coincidence, Tru- jillo and Sheppard started to examine more in detail the orbits of the two unusual ob- jects, along with those of about ten other very distant KBOs. In so doing, they dis- covered that they all share (with some de- gree of approximation) similar ω values. Subsequently, the two researchers publish- ed the results of their study, suggesting that the curious crowding of the perihelia close to the ecliptic could be caused and maintained by the orbiting around the Sun of a distant planet yet unknown. Towards the end of 2014, such conclusions aroused the interest of two other researchers, Kon- stantin Batygin and Mike Brown of the Cal- ifornia Institute of Technology (Caltech) in Pasadena; the first has an in-depth know- ledge of orbital dynamics and numerical sim- ulations; the second is a planetary science professor, co-discoverer of numerous trans- Neptunian objects, including Eris and Sedna, and promoter of the downgrading of Pluto to the status of dwarf planet, occurred 10 years ago. In short, not just two ordinary researchers! By carefully re-examining the is- sue, Batygin and Brown realized that there had to be more be- hind these strange “coinciden- ces”. In fact, they soon discov- ered that the perihelia of that small population of KBOs were not only on the same side of the P ercival Lowell, a wealthy as- tronomer of whom this year marks the cente- nary of his death, was the first to assiduously de- vote himself to the search for a large trans-Nep- tunian planet. [Lowell Obs.] Left, a video pro- viding an over- view of the likely existence of Plan- et Nine. [Science AAAS]