We review the standard model of planetary system formation and then compare the theoretical model with recent observations of protoplanetary disks. According to the standard model, planetary formation begins with dust particle settling to the central plane of a protoplanetary disk to form a thin dust layer around the central plane. Soon the dust layer fragments into a number of planetesimals owing to gravitational instability. After that, those planetesimals coalesce to form terrestrial planets and cores of Jovian planets. Of these processes, particle settling can now be observable. Dust particles around the disk surface absorb the central star radiation and heat up the disk. If particle settling begins, the absorption surface of central star radiation becomes lower than the gaseous disk surface itself, and it affects heating rate and hence temperature distribution in the disk. As a result, the spectrum of thermal emission from the disk is also affected. We theoretically calculate temperature distributions in the disks and spectra of thermal emission from those disks at several stages of particle settling and compare the theoretical spectra with observed ones. From the comparison, we will see that particle settling predicted by the standard mode really occur in many observed protoplanetary disks.
IAU Joint Discussion
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