Free Astronomy Magazine September-October 2014

41 PLANETOLOGY SEPTEMBER-OCTOBER 2014 A large number of stars, perhaps more than half the existing ones, belongs to binary systems, and contrary to what believed in the past they too can host planets. Now it has been shown that precisely those environments are at the origin of the most odd planetary orbits. d the weird rbits T he discovery of hundreds of planetary systems in our corner of the Milky Way, has helped us to understand, during the last two decades, that there may be very different scenarios from those that seemed obvious to us solely by observing our solar system. We did not believe, for example, that there could be plan- ets around the stars of a binary system, when, instead, those too exist. Additionally, it seemed reasonable to assume that also the other planetary systems were as ordered as ours, with circular or- bits more or less coplanar with the stellar equator. Contrarily, it turned out that there is a large number of exoplanets that have highly eccentric and inclined orbits, previously thought to be typ- ical only of comets. Since all protoplanetary disks have a toroidal shape that tends to flatten out (save for the different scale distin- guishing them), how come that planets can end up describing or- bits very different from those travelled by the material from which they formed; orbits which cannot be explained with the simple gravitational interaction between the planets themselves?