Dust Evolution & Planet Traps: Effects on Planet Populations Research
Explore the effects of dust evolution and planet traps on planet populations through a detailed study combining evolving disk structure models, planet formation mechanisms, and population synthesis. Discover the implications for understanding the origin of various planet classes seen on the M-a diagram.
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Dust Evolution & Planet Traps: Effects on Planet Populations Matthew Alessi & Ralph Pudritz McMaster University ExSoCal 2018 September 17, 2018
Goals Want to understand the origin of various planet classes seen on M-a diagram! Generated using data from exoplanets.org (Han + 2014). Current as of Oct. 16, 2017
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 < 10-15 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.
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
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).
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).
Dust Evolution + Population Synthesis Addition of dust model into population synthesis results in forming many super Earths between 0.1-1 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).
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 0.1-1 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.
