Free Astronomy Magazine September-October 2014

light small inner portions of those disks, insufficient to accurately determine their orientation in space and rota- tional properties. Moreover, it does not suffice that only one of the two stars has a disk, but it is necessary that both possess it and that the two disks appear markedly misaligned. Only a scenario of this type can guarantee that at least one of the two disks is sufficiently inclined with respect to the orbital plane of the stars to be desta- bilized by the gravitational interaction of the companion star. As a result we will have planets characterized by “ir- regular” orbits. To understand whether bi- nary systems can actually be one of the causes (if not the sole cause) for the existence of planetary orbits very dis- similar from those found in our solar system was there- fore necessary to find an ideal subject to study, represented by a binary with two disks, both sufficiently bright to allow to highlight their orien- tation in three dimensions and their internal dynamics. Because protoplanetary disks are relatively cool structures, SEPTEMBER-OCTOBER 2014 PLANETOLOGY I n the video, a flight in the nebu- lar star-forming regions of Taurus, and as far as HK Tauri. [ESO/Digi- tized Sky Survey 2/N, Nick Risinger] In the wide-field image, a red arrow shows the position of the HK Tauri system, appearing here as a single star. [ESO/DSS2] Astronomers do not agree on the possi- ble causes of those “wild” orbits, but differ- ent models and subsequent simulations would invoke the presence of a companion star, located on an orbit significantly in- clined with respect to the orbital plane of the planets. To account for the many ob- served scenarios, the inclination required must reach at least a few tens of degrees –a value seemingly easy to verify. Unfortu- nately there are several intervening factors that complicate the researchers task, such as the general impossibility to accurately mea- sure the orbital orientation in three dimen- sions of extrasolar planets; the difficulty of determining in reasonably short times the orientation of the orbital plane of the bi- nary star system; or finally, the companion star could be so faint or so far from the pri- mary to have not yet been recognized. One method that allows to work around this obstacle is that to study not so much the dynamic properties of the already formed planets, but rather those of the environments in which they form; namely, the protoplanetary disks. These structures are far easier to observe than planets, since enormously larger, brighter and more straightforward to spectroscopically re- solve and analyze. Unfortunately, the observation of the rare gas and dust disks present in binary sys- tems composed of young stars (unavoid- ably young) has not in the past led to any significant results, as the instruments used (typically sensitive to the visible light and near-infrared spectrum) could only high-