Free Astronomy Magazine January-February 2015

PLANETOLOGY etary system, which are not yet fully clear. To date, the only attempt to realistically in- terpret HL Tauri puts in relation the rapid planetary formation process with the pres- ence of gas jets produced by a magnetic field and released along the rotation axes of the disk; jets that by colliding at hun- dreds of km/s with the interstellar dust and gas (with lower density) dispersed around the HL Tauri system form the Herbig-Haro object associated to that star (HH 150). But while we wait for more precise interpreta- tions, we can in the meantime admire the amazing im- age of that disk and re- flect on the s imi l a r i t i e s that it could have with the scenario that 4.6 bil- lion years ago heralded the birth of a planetary system parti- cularly fami- liar to us. around HL Tauri there are at least a couple of planets in an advanced stage of forma- tion –a process that must necessarily be un- derway for at least a few hundred thou- sand years. Since it is totally unexpected that processes of that type could start so early in relation to a star evolutionary times, it is fundamental to understand why this happened and if that earliness can re- present an exception or the rule. The an- swers to such questions will allow to more accurately understand also the timing and circumstances of the formation of our plan- C omparison between the size of HL Tauri’s disk and those of our solar system (up to Neptune’s orbit). Even though the Tau- rus young star has a mass close to half that of the Sun, the disk that surrounds it is awesome. Proba- bly our proto- planetary disk was even larger. [ALMA (ESO/ NAOJ/NRAO)] Below, instead, the original im- age is confronted with a hydrody- namic simulation. The similarity between the two is impressive. [Dept. of Physics, University of Milan, Italy] n