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Radial Gradients in Dust Opacity Lead to Preferred Region for Giant Planet Formation

Chachan, Yayaati and Lee, Eve J. and Knutson, Heather A. (2021) Radial Gradients in Dust Opacity Lead to Preferred Region for Giant Planet Formation. . (Unpublished)

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The Rosseland mean opacity of dust in protoplanetary disks is often calculated assuming the interstellar medium (ISM) size distribution and a constant dust-to-gas ratio. However, the dust size distribution and the dust-to-gas ratio in protoplanetary disks are distinct from those of the ISM. Here, we use simple dust evolution models that incorporate grain growth and transport to calculate the time evolution of mean opacity of dust grains as a function of distance from the star. Dust dynamics and size distribution are sensitive to the assumed value of the turbulence strength α_t and the velocity at which grains fragment v_(frag). For moderate-to-low turbulence strengths of α_t≲10⁻³ and substantial differences in vfrag for icy and ice-free grains, we find a spatially non-uniform dust-to-gas ratio and grain size distribution that deviate significantly from the ISM values, in agreement with previous studies. The effect of non-uniform dust-to-gas ratio on the Rosseland mean opacity dominates over that of the size distribution. Spatially varying−that is non-monotonic−dust opacity creates a region in the protoplanetary disk that is optimal for producing hydrogen-rich planets, potentially explaining the apparent peak in gas giant planet occurrence rate at intermediate distances. Enhanced opacities within the ice line also suppress gas accretion rates onto sub-Neptune cores, thus stifling their tendency to undergo runaway gas accretion within disk lifetimes. Finally, our work corroborates the idea that low mass cores with large primordial gaseous envelopes ('super-puffs') originate beyond the ice line.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Chachan, Yayaati0000-0003-1728-8269
Lee, Eve J.0000-0002-1228-9820
Knutson, Heather A.0000-0002-5375-4725
Additional Information:We are indebted to Dave Stevenson and Yanqin Wu for giving us feedback on this manuscript. Y.C. is grateful to Til Birnstiel for providing excellent public repositories that this work relies on. Support for this work was provided by NASA through Space Telescope Science Institute grants GO-14682 and GO-15138.
Group:Astronomy Department
Funding AgencyGrant Number
Space Telescope Science InstituteGO-14682
Space Telescope Science InstituteGO-15138
Record Number:CaltechAUTHORS:20210330-130354103
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108584
Deposited By: Tony Diaz
Deposited On:30 Mar 2021 22:12
Last Modified:30 Mar 2021 22:12

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