Effect of Variable Turbulent Viscosity α and Planet-Induced Gaps on Disk structure, Evolution and the Transport of Water
Abstract
The composition of planets and their volatile contents are intimately connected to the structure and evolution of the parent protoplanetary disks from which they form. How disks evolve has long been a mystery. Its angular momentum transport is often parameterized by a turbulent viscosity parameter α, usually assumed to be spatially and temporally uniform across the disk. I show that variable α(r,z) (where r is radius, and z is height from the midplane) resulting from angular momentum transport due to MRI can yield disks with significantly different structure, with mass piling up in the 1-10 AU region resulting in steep slopes of p > 2 (where p is the power law exponent in Σ ∝ r-p) in these regions. I also show that the transition radius (where bulk mass flow switches from inward to outward) can move in as close 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 α. 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 of a disk likely evolving due to winds and hydrodynamical instabilities, and motivated by meteoritic constraints, that appears consistent with inferred water contents observed in asteroids. Finally, I consider water transport in pre-transition disks, i.e., with gaps carved out by proto-planets, around M, G and A stars. I test how the water content of terrestrial planets that form inward of this gap is affected and may vary in disks around different stars.
- Publication:
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American Astronomical Society Meeting Abstracts #233
- Pub Date:
- January 2019
- Bibcode:
- 2019AAS...23334004K