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Radial Gradients in Dust-to-gas Ratio Lead to Preferred Region for Giant Planet Formation

Chachan, Yayaati and Lee, Eve J. and Knutson, Heather A. (2021) Radial Gradients in Dust-to-gas Ratio Lead to Preferred Region for Giant Planet Formation. Astrophysical Journal, 919 (1). Art. No. 63. ISSN 0004-637X. doi:10.3847/1538-4357/ac0bb6.

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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 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 the 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 v_(frag) for icy and ice-free grains, we find a spatially nonuniform dust-to-gas ratio and grain size distribution that deviate significantly from the ISM values, in agreement with previous studies. The effect of a nonuniform dust-to-gas ratio on the Rosseland mean opacity dominates over that of the size distribution. This spatially varying—that is, non-monotonic—dust-to-gas ratio creates a region in the protoplanetary disk that is optimal for producing hydrogen-rich planets, potentially explaining the apparent peak in the gas-giant planet occurrence rate at intermediate distances. The enhanced dust-to-gas ratio within the ice line also suppresses 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:Article
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URLURL TypeDescription Paper
Chachan, Yayaati0000-0003-1728-8269
Lee, Eve J.0000-0002-1228-9820
Knutson, Heather A.0000-0002-5375-4725
Alternate Title:Radial Gradients in Dust Opacity Lead to Preferred Region for Giant Planet Formation
Additional Information:© 2021. The American Astronomical Society. Received 2020 December 20; revised 2021 June 2; accepted 2021 June 14; published 2021 September 24. We are grateful to the referees for providing us with thoughtful suggestions that improved the paper. We are indebted to Dave Stevenson, Yanqin Wu, and Chris Ormel for giving us feedback on this manuscript. Y.C. is grateful to Til Birnstiel for providing the excellent public repositories that this work relies on. Support for this work was provided by NASA through Space Telescope Science Institute grant GO-15138.
Funding AgencyGrant Number
Subject Keywords:Planet formation; Protoplanetary disks; Gas-to-dust ratio; Extrasolar gaseous giant planets; Mini Neptunes
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Planet formation (1241); Protoplanetary disks (1300); Gas-to-dust ratio (638); Extrasolar gaseous giant planets (509); Mini Neptunes (1063)
Record Number:CaltechAUTHORS:20210330-130354103
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Official Citation:Yayaati Chachan et al 2021 ApJ 919 63
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:28 Sep 2021 19:58

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