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

Chachan, Yayaati; Lee, Eve J.; Knutson, Heather A.

doi:10.3847/1538-4357/ac0bb6

Cited by 22 publications

(14 citation statements)

References 131 publications

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“…The presence of rings is not a unique solution for explaining the extremely low bulk density of exoplanets. A large atmospheric mass fraction naturally causes inflated planetary radii (e.g., Lopez & Fortney 2014), which may originate from planet formation far away from a planet's current orbit (Lee & Chiang 2016;Chachan et al 2021). Strong interior heating can also cause the inflated radius (Millholland 2019).…”

Section: How To Distinguish Ringed Low-density Exoplanets From Other ...mentioning

confidence: 99%

A Framework for Characterizing Transmission Spectra of Exoplanets with Circumplanetary Rings

Ohno

Fortney

2022

ApJ

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Recent observations revealed that several extremely low-density exoplanets show featureless transmission spectra. While atmospheric aerosols are a promising explanation for both the low-density and featureless spectra, there is another attractive possibility: the presence of circumplanetary rings. Previous studies suggested that rings cause anomalously large transit radii. However, it remains poorly understood how rings affect the transmission spectrum. Here, we provide a framework to characterize the transmission spectra of ringed exoplanets. We develop an analytical prescription to include rings in the transmission spectra for arbitrarily viewing geometries. We also establish a simple postprocessing model that can include the ring’s effects on precomputed ring-free spectra. The ring flattens the transmission spectrum for a wide range of viewing geometries, consistent with the featureless spectra of extremely low-density exoplanets. Near-future observations by the James Webb Space Telescope at longer wavelengths would be able to distinguish the aerosol and ring scenarios. We also find that rocky rings might cause a silicate feature at ∼10 μm if the ring’s optical depth is around unity. Thus, the ring’s spectral features, if detected, would provide tight constrains on the physical properties of exoplanetary rings. We also discuss the ring’s stability and suggest that thick rings are sustainable only at the equilibrium temperature of ≲300 K for the ring’s age comparable to Kepler planets. This might indicate the intrinsic deficit of thick rings in the Kepler samples, unless rings are much younger than the planets as suggested for Saturn.

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Section: How To Distinguish Ringed Low-density Exoplanets From Other ...mentioning

confidence: 99%

A Framework for Characterizing Transmission Spectra of Exoplanets with Circumplanetary Rings

Ohno

Fortney

2022

ApJ

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Section: How To Distinguish Ringed Low-density Exoplanets From Other ...mentioning

confidence: 99%

A Framework for Characterizing Transmission Spectra of Exoplanets with Circumplanetary Rings

Ohno,

Fortney

2022

Preprint

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Recent observations revealed that several extremely low-density exoplanets show featureless transmission spectra. While atmospheric aerosols are a promising explanation for both the low density and featureless spectra, there is another attractive possibility: the presence of circumplanetary rings. Previous studies suggested that rings cause anomalously large transit radii. However, it remains poorly understood how rings affect the transmission spectrum. Here, we provide a framework to characterize the transmission spectra of ringed exoplanets. We develop an analytical prescription to include rings in the transmission spectra for arbitrarily viewing geometries. We also establish a simple post-processing model that can include the ring's effects on precomputed ring-free spectra. The ring flattens the transmission spectrum for a wide range of viewing geometries, consistent with the featureless spectra of extremely low-density exoplanets. Near-future observations by JWST at longer wavelengths would be able to distinguish the aerosol and ring scenarios. We also find that rocky rings might cause a silicate feature at ∼ 10 µm if the ring's optical depth is around unity. Thus, the ring's spectral features, if detected, would provide tight constrains on the physical properties of exoplanetary rings. We also discuss the ring's stability and suggest that thick rings are sustainable only at the equilibrium temperature of 300 K for the ring's age comparable to Kepler planets. This might indicate the intrinsic deficit of thick rings in the Kepler samples, unless rings are much younger than the planets as suggested for Saturn.

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“…The dust opacity derived by Valencia et al (2013) is significantly higher than suggested by other studies (Mordasini et al 2014;Ormel 2014;Brouwers et al 2021). However, the grain opacity is expected to be high at early phases of the planetary growth when the protoplanet accretes pebbles due to efficient pebble fragmentation (Brouwers et al 2021;Chachan et al 2021), pebble ablation (e.g., Valletta & Helled 2020), and bouncing collisions between accreted pebbles (Ormel et al 2021).…”

Section: Appendix a The Importance Of Opacity And Composition Of The ...mentioning

confidence: 75%

Possible In Situ Formation of Uranus and Neptune via Pebble Accretion

Valletta¹,

Helled²

2022

ApJ

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The origin of Uranus and Neptune is still unknown. In particular, it has been challenging for planet formation models to form the planets in their current radial distances within the expected lifetime of the solar nebula. In this paper, we simulate the in situ formation of Uranus and Neptune via pebble accretion and show that both planets can form within ∼3 Myr at their current locations, and have final compositions that are consistent with the heavy element to H–He ratios predicted by structure models. We find that Uranus and Neptune could have been formed at their current locations. In several cases a few earth masses (M ⊕ ) of heavy elements are missing, suggesting that Uranus and/or Neptune may have accreted ∼1–3 M⊕ of heavy elements after their formation via planetesimal accretion and/or giant impacts.

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

Cited by 22 publications

References 131 publications

A Framework for Characterizing Transmission Spectra of Exoplanets with Circumplanetary Rings

A Framework for Characterizing Transmission Spectra of Exoplanets with Circumplanetary Rings

A Framework for Characterizing Transmission Spectra of Exoplanets with Circumplanetary Rings

Possible In Situ Formation of Uranus and Neptune via Pebble Accretion

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