Free Astronomy Magazine

45 MAY-JUNE 2014 DWARF PLANETS of a planet of consider- able size, which in transit- ing in the Edgeworth-Kuiper belt would have perturbed the or- bits of countless icy bodies, driving them in the outer space. The ejected plan- et might have definitively abandoned the sphere of influence of the Sun, or it may have positioned itself in an extremely wide orbit, thus remaining invisible even in the most powerful instruments. The second model, instead, predicts that the inner Oort Cloud was formed by the dis- ruption caused by a s tar passing at a relative- ly close distance from the solar system. This would have happened within the first 10 million years of the system’s life, when the Sun was still in the company of its “sisters” birthed from a common molecular cloud. A variant of this second model presumes that objects like Sedna and 2012 VP 113 might have been ac- creted by planetesimals ripped away by the Sun from another star, also in this case when the two stars were still part of the same cluster. Given that at present the objects for sure belonging to the new population are only a couple, it is too early to say which model is applicable, but since the different scenarios presume different orbital configurations, it will be sufficient to wait for the discovery of other same-type objects to see which prediction is more realistic. While Trujillo and Sheppard do not exclude any hypothesis, they point out that the key to accurately defining the physical char- acteristics of the inner Oort Cloud may already exist. In fact, Sed- na and 2012 VP 113 have, more than anything else, similar values of argument of perihelion ( ω ): 311° for the first, 293° for the second – a mini- mum difference that made re- searchers s u s p i - cious. I n the back- ground: the ap- proximate posi- tions of 2012 VP 113 and Sedna on their orbits. In the box: the three images of the discovery combined in the colour version (RGB). [C. Trujillo and S. Sheppard]