1. Dust Evolution & Planet Traps: Effects on Planet Populations
Matthew Alessi & Ralph Pudritz
McMaster University
ExSoCal 2018
September 17, 2018

2. Goals
Want to understand the origin of various planet classes seen on M-a diagram!
Generated using data from exoplanets.org (Han ). Current as of Oct. 16, 2017

3. Model Overview & Planet Traps
Combine models of:
Evolving physical and chemical protoplanetary disk structure.
Planet formation via core accretion.
Planet migration (trapped type-I for MP < MEarth; type-II for heavier planets).
Planet traps:
Ice line
heat transition
dead zone outer edge.
Alessi, Pudritz & Cridland, 2017, MNRAS, 464, 428.
Hasegawa Y., Pudritz R. E., MNRAS, 2011, 417, 1236.

4. Planet Population Synthesis
Stochastically sample from observationally constrained distributions of disk mass, lifetime, and metallicity.
Our constant dust-to-gas ratio model cannot populate a region of zone 5 corresponding to low-period super Earths.
Assuming a globally constant dust-to-gas ratio of 1/100, model cannot produce low-mass, low-period super Earths.
Alessi & Pudritz, 2018

5. Dust Evolution Model Birnstiel et al. 2012 dust model. 3 regimes:
Outer disk (outside ice line): drift limited regime. High fragmentation barrier (ice coated grains), large grains migrate to inner disk quickly through radial drift.
Inner disk (within ice line): fragmentation limited regime. Low fragmentation barrier limits growth, longer drift timescale.
Ice line: transition between fragmentation regimes. Dust piles up here at early times, simulating “dust trapping”.
Birnstiel et al. 2012
Alessi, Pudritz, & Cridland (in prep).

6. Dust Evolution + Population Synthesis
Ice Line: Efficient production of gas giants! Growth at a solid density enhancement.
Heat transition: Low dust densities outside ice line cause inefficient growth.
Dead Zone: Trap begins in outer disk, evolves to within the ice line after 1Myr, delayed growth.
Alessi, Pudritz, & Cridland (in prep).

7. Dust Evolution + Population Synthesis
Addition of dust model into population synthesis results in forming many super Earths between AU! Improvement over constant dust-to-gas model.
This model also produces too many zone 3 gas giants from efficient growth at the ice line. Indicates radial drift model is too efficient, in agreement with observations.
Alessi, Pudritz, & Cridland (in prep).

8. Conclusions & Future Work
Constant dust-to-gas ratio model (Alessi & Pudritz 2018):
Low opacities (~10-3 cm2 g-1) are necessary to form gas giants out to 3 AU.
X-ray ionization is necessary to obtain a separation between the hot Jupiter and warm Jupiter populations
Constant dust-to-gas ratio model cannot produce low-mass, short-period super Earths.
Dust evolution model (Alessi, Pudritz, & Cridland, in prep.):
Adding dust evolution model into population synthesis approach results in formation of super Earths between AU.
Produces too many gas giants; efficient radial drift piles up dust at ice line resulting in short planet formation timescales.
Future work:
Incorporating chemistry into planet populations to see variety among super Earth compositions.
Determine the amount of structure in M-a diagram that results from scattering effects by including dynamics in model.