Effect of disk structure on the distribution of water in protoplanetary disks and planets

The composition of planets and their volatile contents are intimately connected to the structure and evolution of their parent protoplanetary disks. The transport of momentum and volatiles is often parameterized by a turbulent viscosity parameter $\alpha$, which is usually assumed to be spatially and temporally uniform across the disk. I show that variable $\alpha$(r,z) (where $r$ is radius, and $z$ is height from the midplane) attributable to angular momentum transport due to MRI can yield disks with significantly different structure, as mass piles up in the 1-10 AU region resulting in steep slopes of p $>$ 2 here (where p is the power law exponent in $\Sigma \propto r^{-p}$). I also show that the transition radius (where bulk mass flow switches from inward to outward) can move as close in as 3 AU; this effect (especially prominent in externally photoevaporated disks) may significantly influence the radial water content available during planet formation.

I then investigate the transport of water in disks with different variable α profiles. While radial temperature profile sets the location of the water snowline (i.e., inside of which water is present as vapor; outside of which, as ice on solids), it is the rates of diffusion and drift of small icy solids and diffusion of vapor across the snow line that determine the radial water distribution. All of these processes are highly sensitive to local $\alpha$. I calculate the effect of radially varying α on water transport, by tracking the abundance of vapor in the inner disk, and fraction of ice in particles and larger asteroids beyond the snow line. I find one α profile attributable to winds and hydrodynamical instabilities, and motivated by meteoritic constraints, to show considerable agreement with inferred water contents observed in solar system asteroids.

Finally, I calculate the timing of gap formation due to the formation of a planet in disks around different stars. Here, I assume that pebble accretion is the dominant mechanism for planetary growth and that the core of the first protoplanet forms at the water snow line. I discuss the dependence of gap timing to various stellar and disk properties.