Free Astronomy Magazine

PLANETOLOGY Jupiter could be re- sponsible for the lack of homoge- neity within the cloud and, conse- quently, of the pref- erential paths fol- lowed by the com- ets. Also in this case no direct evidence was found, but it was nonetheless de- cided to give a use- less name to the hypothetical plan- et, Tyche, the Greek goddess of fortune. In short, on several occasions and for various reasons it had been necessary to hypothesize the presence of a giant planet or a stellar body, positioned somewhere between Pluto’s orbit and the Oort Cloud, with a sufficiently eccentric orbit to bring it to directly or indirectly interact with other bodies of our solar system. In some cases it has perhaps been more an attempt to try to lend substance to a myth than to propose a viable solution to unsolved prob- lems, given that for these same problems were later found much more simple and convincing explanations. In not being how- ever possible to consider the Planet X issue conclusively settled without at the same time also remove any slightest doubt, astronomers have been waiting for indis- putable proof before putting an end to this centuries-old myth. These proofs have emerged from the data- base of the second all-sky survey perform- ed by the WISE satellite (Wide-field Infra- red Survey Explorer), released by NASA last November and immediately examined by researchers who were eagerly waiting to compare its astrometric data with that of S ummary table of the outer so- lar system show- ing groups of Centaurs, Pluti- nos and objects of the Kuiper belt. Much more further away known objects are at present a small number. Below: the orbit of Tyche, the hy- pothetical Planet X whose exis- tence was predict- ed in the late ‘90s.