Free Astronomy Magazine

or non-existence is not provable. (In a high- ly developed civilization it should not be necessary to prove the non-existence of something whose existence has not been demonstrated, but evidently our civiliza- tion is not sufficiently advanced.) The open discussions about Planet X ended (in the scientific world) when, from the data col- lected by Voyager 2, astronomers realized that Neptune’s mass was different from that previously estimated and that the new value measured by the probe no longer required the existence of a large planet beyond Pluto to account for the sup- posed residual in- consistencies on the mo- tions of Ur a - nus and Nep- tune. As often hap- pens when the truth is disappointing, many devotees of mat- ters not strictly scien- tific have however continued to be- lieve in the ex i s t ence of Planet X, match that predicted by the astronomers’ calculations. The dis- crepancy between the theoretical and the ob- served positions, led to assume that there might be an additional outer plan- et which, due to its mass and thus its gravitational force, was responsible for the inconsistencies found. The extensive searches for that object re- sulted in the almost accidental discovery in 1930 of Pluto, a planet whose mass soon proved to be largely insufficient to justify such discrepancy. Planet X started from that point on to become a real challenge, but the instruments, methods and amount of time available to astronomers in the half century following Pluto’s discovery were insufficient to verify the existence of orbiting objects at such great distances from the Sun, and this helped to transform that hypothetical presence in a topic on which to speculate freely, just like with everything else whose existence MAY-JUNE 2014 PLANETOLOGY 30