Explaining transition disks without massive planets

Abstract

<p>Transition disks are one of the enigmas of the planet formation process: These objects typically feature wide gaps in the dust component, along with deficit of NIR emission corresponding to a lack of small grains in the inner regions, but simultaneously require a gas rich inner disk capable of sustaining high accretion rates, and a high content of pebble sized grains to explain the emission detected in the millimeter continuum. <br />Massive planets of several Jupiter masses have been long proposed as an explanation for these objects. However, despite the efforts to find these giants, only one or two disks have confirmed detections of a planetary companion. We propose a new hybrid model that easily explain the properties of transition disks, by combining the contributions made by different research groups over the last decade in photoevaporation, dead zones, and dust trapping. In our model photoevaporation takes care of opening a cavity in the gas and dust component, while dead zones in the inner regions lead to long lived-inner disk, capable of sustaining the observed accretion rates during the photoevaporative dispersal process. Finally, dust trapped in moderate substructures (such as the ones caused by small Saturn mass planets) can explain the emissions found in the millimeter continuum, without imposing strong constrains on the planet location. <br />With our model we show that instead of invoking massive fine-tuned planets to explain all the transition disk properties, the different processes that occur in protoplanetary disks complement each other and naturally reproduce the transition disk observations. Then, perhaps the reason of why we don't find more hidden massive planets is, simply, because they are not there.</p>