Simulating Disk Dynamics and Investigating their Exoplanet Outcomes

Ellen M. Price

16 Sep 2020

Organization of this talk

  1. Protoplanetary disk projects
    1. Past: Chemistry Along Accretion Streams in a Viscously Evolving Protoplanetary Disk

Organization of this talk

  1. Protoplanetary disk projects
    1. Past: Chemistry Along Accretion Streams in a Viscously Evolving Protoplanetary Disk
    2. Present: Project Fruitypebbles

Organization of this talk

  1. Protoplanetary disk projects
    1. Past: Chemistry Along Accretion Streams in a Viscously Evolving Protoplanetary Disk
    2. Present: Project Fruitypebbles
    3. Future: Simulating Protoplanetary Disk Chemistry in the Presence of Dust Drift, Vortices, and Warps

Organization of this talk

  1. Protoplanetary disk projects
    1. Past: Chemistry Along Accretion Streams in a Viscously Evolving Protoplanetary Disk
    2. Present: Project Fruitypebbles
    3. Future: Simulating Protoplanetary Disk Chemistry in the Presence of Dust Drift, Vortices, and Warps
  2. Exoplanets projects
    1. Past: Tidally Distorted, Iron-enhanced Exoplanets Closely Orbiting Their Stars

Organization of this talk

  1. Protoplanetary disk projects
    1. Past: Chemistry Along Accretion Streams in a Viscously Evolving Protoplanetary Disk
    2. Present: Project Fruitypebbles
    3. Future: Simulating Protoplanetary Disk Chemistry in the Presence of Dust Drift, Vortices, and Warps
  2. Exoplanets projects
    1. Past: Tidally Distorted, Iron-enhanced Exoplanets Closely Orbiting Their Stars
    2. Future: Ultra-short period planet interiors?

Past: Chemistry Along Accretion Streams in a Viscously Evolving Protoplanetary Disk

with Ilse Cleeves and Karin Öberg

arXiv:2002.04651

Science case

  • In this field, we commonly see disk models that choose to focus on either dynamics or chemistry
  • Can we uncover interesting features by combining the two effects in a simple but meaningful way?

Disk processes

Project goals

Integrate a full (> 600 species) chemical network into a simple dynamics framework that assumes well-coupled gas and dust and “follows” material around the disk (Lagrangian fluid picture)

Methods

  1. Obtain a self-consistent temperature structure
    1. Use a 1-dimensional disk model that solves the Lynden-Bell & Pringle (1974) equation for surface density evolution
    2. Run RADMC-3D, a radiative transfer code
    3. Update temperature and loop until converged
  2. Compute material “tracks” through the disk
  3. Run chemistry evolution as post-processing step, using evolving track conditions

Track properties

Enhancement and depletion

Enhancement and depletion

Takeaways

  • Accretion really matters!
  • We find orders of magnitude enhancement and depletion in some species, including hydrocarbons
  • The most abundant species are not significantly impacted, however

Questions?

Present: Project Fruitypebbles

with Ilse Cleeves and Karin Öberg

Why the name??

  • The primary difference between this model and the last is the inclusion of differential motion between gas and dust/pebbles.
  • If this model eventually includes a “full” chemical network, then we might reasonably see organic molecules forming in the solid phase.

Science case

  • We have observed two comets, 2I/Borisov and C/2016 R2 (PanSTARRS), which have enhanced CO compared to H2O.
  • There is no universally-accepted explanation for the enhancement! Most comets in our solar system are predominantly water.
  • C/2016 R2 (PanSTARRS) originates in our own solar system, so we need a theory that can explain mostly water-based comets with a few outliers.

Model details

  • Gas surface density evolution is given by the classical Lynden-Bell & Pringle (1974) PDE
  • Dust surface density is given by equations in Birnstiel et al. (2010): dust advects along with the gas, but with imperfect coupling according to the Reynolds number
  • H2O and CO simulated in the gas phase and on solids, and can move between phases but do not react

More model details

  • The disk is solved in one dimension
  • Densities are given vertical Gaussian distributions and adsorption/desorption rates are vertically integrated where appropriate
  • First production use of the github:emprice/benzaiten library for mathematical manipulation
  • Timestepping uses BDF implementation in PETSc; second-order-accurate spatial derivatives with finite difference approximations

What do we find?

We see pockets of space and time where CO-rich ice develops purely because of drift and freezeout!

Fiducial model

All model cases

Takeaways

  • More initial CO → greater enhancement by 1 Myr.
  • No matter the initial CO level, drift efficiency, viscous spreading, or temperature, we always find some pocket of space and time where the CO/H2O is about or exceeds 1.
  • The drift efficiency and viscosity parameters “move” the funnel of enhancement in space-time.

Questions?

Future: Simulating Protoplanetary Disk Chemistry in the Presence of Dust Drift, Vortices, and Warps

Overview

  1. Extend the Fruitypebbles model to include a more complete chemical network with reactions
  2. Use/modify a hydrodynamics code, like Athena++, to include chemistry and simulate the same disk, but in full 3-d space
  3. Further extend this code to include a vortex or warp to better understand and predict chemical signatures that may be left behind

Questions?

Past: Tidally Distorted, Iron-enhanced Exoplanets Closely Orbiting Their Stars

with Leslie Rogers

arXiv:1901.10666

Science case

  • Ultra-short period planets (planets with $P$ < 1 day) have been found in the Kepler and TESS fields
  • These planets are so close to their stars that non-spherical shapes are possible, distorting our measurements of masses and radii
  • Can we self-consistently model USP planet shapes for realistic equations of state to better understand planets like KOI-1843.03?

Typical planet: KOI-1843.03

  • Discovery reported in Rappaport et al. (2013)
  • Orbital period just 4.2 hr!
  • Initial density estimate was ≥ 7 g/cm3, based on Roche limit arguments, but this assumed a spherical shape

Model details

Broadly follows Hachisu (1986a,b) with some important changes

  • We want a point-source host star at some fixed radius away from the planet; original method had full rotational symmetry
  • Use a modified polytrope equation of state (see Seager et al. 2007) instead of normal polytrope that is appropriate for stars

Simulation geometry

More model details

  1. Assume a constant-density ellipsoid with fixed aspect ratio
    1. Compute the gravitational potential at all points in the computational domain
    2. Convert potential to enthalpy and enthalpy back to density
    3. Loop until convergence
  2. Save the output for the next model, which we fix to be slightly more distorted

Minimum orbital period, Fe cores

Minimum orbital period, FeS cores

Aspect ratio estimation

Takeaways

  • By assuming the planet is at the Roche limit, we can constrain its potential composition using transit measurements alone!
  • KOI-1843.03 is probably not consistent with the FeS core composition
  • KOI-1843.03 may be very distorted

Questions?

Future: Ultra-short period planet interiors?

Organization of this talk

  1. Protoplanetary disk projects
    1. Past: Chemistry Along Accretion Streams in a Viscously Evolving Protoplanetary Disk

Organization of this talk

  1. Protoplanetary disk projects
    1. Past: Chemistry Along Accretion Streams in a Viscously Evolving Protoplanetary Disk
    2. Present: Project Fruitypebbles

Organization of this talk

  1. Protoplanetary disk projects
    1. Past: Chemistry Along Accretion Streams in a Viscously Evolving Protoplanetary Disk
    2. Present: Project Fruitypebbles
    3. Future: Simulating Protoplanetary Disk Chemistry in the Presence of Dust Drift, Vortices, and Warps

Organization of this talk

  1. Protoplanetary disk projects
    1. Past: Chemistry Along Accretion Streams in a Viscously Evolving Protoplanetary Disk
    2. Present: Project Fruitypebbles
    3. Future: Simulating Protoplanetary Disk Chemistry in the Presence of Dust Drift, Vortices, and Warps
  2. Exoplanets projects
    1. Past: Tidally Distorted, Iron-enhanced Exoplanets Closely Orbiting Their Stars

Organization of this talk

  1. Protoplanetary disk projects
    1. Past: Chemistry Along Accretion Streams in a Viscously Evolving Protoplanetary Disk
    2. Present: Project Fruitypebbles
    3. Future: Simulating Protoplanetary Disk Chemistry in the Presence of Dust Drift, Vortices, and Warps
  2. Exoplanets projects
    1. Past: Tidally Distorted, Iron-enhanced Exoplanets Closely Orbiting Their Stars
    2. Future: Ultra-short period planet interiors?

Thanks for your attention!