Free Astronomy Magazine September-October 2014

PLANETOLOGY lution and, hence, to conduct spectral anal- ysis on clearly distinct regions of the indi- vidual disks. Now Jensen and Akeson have filled that gap by observing the HK Tauri system with the ALMA telescope at fre- quencies of 230.5 GHz and 345.8 GHz, cov- ering continuum emission from dust and line emission from the carbon monoxide (CO). In this configuration ALMA has pro- vided better medium spatial resolutions of 1 arcsecond and medium spectral resolu- tions of about 1 km/s; in short, adequately sufficient to detect even modest velocities of the material in at least two opposite re- gions of each disk. The choice of frequen- cies to be investigated soon proved to be a wise one, since it is precisely the presence of carbon monoxide in the disks that al- lowed the two researchers to highlight the rotational motion of those structures around their respective stars. This obvi- ously through the redshifts and blueshifts of the line itself, depending on whether it was detected in that part of the disk mov- ing away from the observer or in that mov- ing toward the observer. The results of the observations, published in Nature on last 31 July, indicate that the orientations of the two disks are signifi- cantly different, since the projection of the major axis of the HK Tau A’s disk forms an apparent angle of about 45° with that of HK Tau B, and even ignoring the orien- tation of the orbital plane of the pair of stars, such angle tells us that at least one of the disks is not aligned with that plane. By taking into account the rotational prop- erties of the disks, Jensen and Akeson cal- culated that their actual misalignment should be between 60° and 68°, values which without a doubt have the effect of destabilizing the gravitational interaction of each star on the disk of the other. These findings are consistent with recent simulations of the formation of binary sys- tems, according to which the tendency of the disks is to not be at all aligned with the orbital plane of the stars, especially in sys- tems with semi-major axis greater than 100 AU –i.e., those in which the dissipation mechanisms are unable to quickly align the disks with the orbit. Jensen and Akeson have thus shown that binary star systems are environments that have an important place in the evolution of planetary orbits and can be at the root of the many unex- pected trajectories along which many extra- solar planets appear to be moving. n T his image taken by ALMA, shows the large-scale distribution of the velocities of gas and dust within the two HK Tauri disks. The blue repre- sents the mate- rial moving toward the ob- server and the red that moving away. By study- ing the internal dynamics of those structures, two researchers have shown that the disks are not aligned either with each anoth- er or with the orbital plane of their stars. [NASA/ JPL-Caltech/ R. Hurt (IPAC)]