Abstract
Context.Pressure maxima are regions in protoplanetary disks in which pebbles can be trapped because the regions have no local pressure gradient. These regions could be ideal places in which planetesimals might be formed or to isotopic reservoirs might be isolated. Observations of protoplanetary disks show that dusty ring structures are common, and pressure maxima are sometimes invoked as a possible explanation. In our Solar System, pressure bumps have been suggested as a possible mechanism for separating reservoirs with different nucleosynthetic compositions that are identified among chondrites and iron meteorites. In this paper, we detail a mechanism by which pressure maxima form just inward of the snow line in stratified disks (with a dead zone and an active layer). This mechanism does not require the presence of a planet.Aims.We investigate the conditions for the formation of pressure maxima using a vertically averagedαviscosity model and release of water vapor at the snow line.Methods.We considered a 1Dαdisk model. Using a combination of analytical and numerical investigations, we explored the range of conditions for a pressure maximum to form inside the dead zone and just inward of the snow line.Results.When the vertically averagedαis a decreasing function of the surface density, then the release of water vapor at the snow line decreases the sound velocity, and a pressure bump appears in turn. This requires a constant inflow of icy pebbles with a ratio of the pebble influx to gas influx >0.6 for a power-law disk with a 1% ice-to-gas ratio, and >1.8 for a disk with an ice-to-gas ratio ~0.3%. If these conditions are met, then a pressure maximum appears just inward of the snow line due to a process that couples the dead and active layers at the evaporation front. The pressure bump survives as long as the icy pebble flux is high enough. The formation of the pressure bump is triggered by the decrease in sound velocity inward of the snow line through the release of water vapor.Conclusions.This mechanism is promising for isolating early reservoirs carrying different isotopic signatures in the Solar System and for promoting dry planetesimal formation inward of the snow line, provided the vertically averaged description of a dead zone is valid.
Highlights
Formation of pressure maxima in protoplanetary disks is an active topic of research because these maxima are seen as ideal places in which pebbles might accumulate efficiently and subsequently form planetesimals through the so-called streaming instability process, for example (Johansen et al 2007; Pinilla et al 2012; Drazkowska & Dullemond 2014; Drazkowska & Alibert 2017; Charnoz et al 2019)
This results in a quiet ‘dead’ midplane with equivalent α in the range 10−5 to 10−3 depending on local hydrodynamic turbulence (Bai & Stone 2013; Turner et al 2014; Gressel et al 2015; Kadam et al 2019). It is topped by an active layer with a high accretion 100–1000 kg m−2 rate but (Turner low column density (Σa) in the range et al 2014), and it may have a low level of turbulence (Béthune et al 2017) despite the high accretion rate
Criterion in terms of the mass flux of icy pebbles The criterion derived in Eq (12) does not allow predicting the range of pebble and gas flux for which a pressure bump may form inside a dead zone
Summary
Formation of pressure maxima in protoplanetary disks is an active topic of research because these maxima are seen as ideal places in which pebbles might accumulate efficiently and subsequently form planetesimals through the so-called streaming instability process, for example (Johansen et al 2007; Pinilla et al 2012; Drazkowska & Dullemond 2014; Drazkowska & Alibert 2017; Charnoz et al 2019). For a pressure minimum, drifting pebbles will move away from the minimum For these reasons, a pressure maximum is invoked as a possible dynamical barrier that could be at the origin of a major isotopic heterogeneity observed in Solar System meteorites: Meteorites can be divided into two broad groups because the variations in their stable isotopes do not depend on mass (Trinquier et al 2008; Kruijer et al 2017, 2020; Kleine et al 2020). The very early model age for the accretion of the parent bodies of NC iron meteorites (
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