Chemical Diversity in Protoplanetary Disks and Its Impact on the Formation History of Giant Planets

Pacetti, Elenia; Turrini, D.; Schisano, E.; Molinari, S.; Fonte, S.; Politi, R.; Hennebelle, P.; Klessen, Ralf S.; Testi, L.; Lebreuilly, Ugo

doi:10.3847/1538-4357/ac8b11

“…Chemical reset has a significant influence on the distribution of oxygen and carbon in the circumstellar disk (Eistrup et al 2016(Eistrup et al , 2018. We point the reader to Cridland et al (2019) and Pacetti et al (2022) for a more detailed description of how such a chemical reset would affect the composition of materials accreted by giant planets.…”

Section: C/si Content Of Solidsmentioning

confidence: 99%

Breaking Degeneracies in Formation Histories by Measuring Refractory Content in Gas Giants

Chachan

¹

,

Knutson

²

,

Lothringer

³

et al. 2023

ApJ

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Relating planet formation to atmospheric composition has been a long-standing goal of the planetary science community. So far, most modeling studies have focused on predicting the enrichment of heavy elements and the C/O ratio in giant planet atmospheres. Although this framework provides useful constraints on the potential formation locations of gas giant exoplanets, carbon and oxygen measurements alone are not enough to determine where a given gas giant planet originated. Here, we show that characterizing the abundances of refractory elements (e.g., silicon and iron) can break these degeneracies. Refractory elements are present in the solid phase throughout most of the disk, and their atmospheric abundances therefore reflect the solid-to-gas accretion ratio during formation. We introduce a new framework that parameterizes the atmospheric abundances of gas giant exoplanets in the form of three ratios: Si/H, O/Si, and C/Si. Si/H traces the solid-to-gas accretion ratio of a planet and is loosely equivalent to earlier notions of “metallicity.” For O/Si and C/Si, we present a global picture of their variation with distance and time based on what we know from the solar system meteorites and an updated understanding of the variations of thermal processing within protoplanetary disks. We show that ultrahot Jupiters are ideal targets for atmospheric characterization studies using this framework as we can measure the abundances of refractories, oxygen, and carbon in the gas phase. Finally, we propose that hot Jupiters with silicate clouds and low water abundances might have accreted their envelopes between the soot line and the water snow line.

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“…Superstellar C/O and abundances may be due either to gas accretion close to the CO or CO 2 ice lines, or indicate that the atmosphere was substantially polluted by pebble (early on) or planetesimal (above the pebble isolation mass) accretion and/or core erosion. When migration is significant, the various environments along the path can contribute, leading to less stringent constraints on planet formation (Pacetti et al 2022).…”

Section: Key Results From the Retrieval Analysis For Hr 8799 Cmentioning

confidence: 99%

Retrieving C and O Abundance of HR 8799 c by Combining High- and Low-resolution Data

Ji

¹

,

Wang

²

,

Ruffio

³

et al. 2022

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The formation and evolution pathway for the directly imaged multiplanetary system HR 8799 remains mysterious. Accurate constraints on the chemical composition of the planetary atmosphere(s) are key to solving the mystery. We perform a detailed atmospheric retrieval on HR 8799 c to infer the chemical abundances and abundance ratios using a combination of photometric data along with low- and high-resolution spectroscopic data (R ∼ 20–35,000). We specifically retrieve [C/H], [O/H], and C/O and find them to be 0.55 − 0.39 + 0.36 , 0.47 − 0.32 + 0.31 , and 0.67 − 0.15 + 0.12 at 68% confidence. The superstellar C and O abundances, yet a stellar C/O ratio, reveal a potential formation pathway for HR 8799 c. Planet c, and likely the other gas giant planets in the system, formed early on (likely within ∼1 Myr), followed by further atmospheric enrichment in C and O through the accretion of solids beyond the CO ice line. The enrichment either preceded or took place during the early phase of the inward migration to the current planet locations.

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“…This information uniquely constrains the region(s) in the disk where the planet accreted its gas envelope and solids. Importantly, we show that the current widely-adopted retrieval framework in which one scales either the carbon or oxygen abundance along with the refractories using a global metallicity knob is erroneous (see also Turrini et al 2021;Pacetti et al 2022). Carbon and oxygen abundances should only scale with the refractory abundance beyond the CO snowline, where all the heavy elements are condensed out.…”

Section: Future Work and Conclusionmentioning

confidence: 91%

“…Chemical reset has a significant influence on the distribution of oxygen and carbon in the circumstellar disk (Eistrup et al 2016(Eistrup et al , 2018. We point the reader to Cridland et al (2019) and Pacetti et al (2022) for a more detailed description of how such a chemical reset would affect the composition of materials accreted by giant planets.…”

Section: C/si Content Of Solidsmentioning

confidence: 99%

“…However, stellar hosts span a range of elemental abundances and the ratios of these elements show some correlations with stellar metallicity, with [O/Si] and [C/Si] varying by as much as ∼ 0.5 dex in a given stellar metallicity range (e.g., Ness et al 2018;Buder et al 2018). When applied to individual exoplanetary systems, our model predictions should therefore be rescaled to account for the measured composition of the host star (e.g., Bitsch & Battistini 2019;Turrini et al 2021;Pacetti et al 2022). However, we note that in our discussion of atmospheric chemistry in § 5, it is the number ratios of the relevant elements that determine the equilibrium molecular composition of the atmosphere.…”

Section: Model Assumptions and Caveatsmentioning

confidence: 99%

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Breaking Degeneracies in Formation Histories by Measuring Refractory Content in Gas Giants

Chachan,

Knutson,

Lothringer

et al. 2022

Preprint

View full text Add to dashboard Cite

Relating planet formation to atmospheric composition has been a long-standing goal of the planetary science community. So far, most modeling studies have focused on predicting the enrichment of heavy elements and the C/O ratio in giant planet atmospheres. Although this framework provides useful constraints on the potential formation locations of gas giant exoplanets, carbon and oxygen measurements alone are not enough to determine where a given gas giant planet originated. Here, we show that characterizing the abundances of refractory elements (e.g., silicon, iron) can break these degeneracies. Refractory elements are present in the solid phase throughout most of the disk and their atmospheric abundances therefore reflect the solid-to-gas accretion ratio during formation. We introduce a new framework that parameterizes the atmospheric abundances of gas giant exoplanets in the form of three ratios: Si/H, O/Si, and C/Si. Si/H traces the solid-to-gas accretion ratio of a planet and is loosely equivalent to earlier notions of 'metallicity'. For O/Si and C/Si, we present a global picture of their variation with distance and time based on what we know from the solar system meteorites and an updated understanding of the variations of thermal processing within protoplanetary disks. We show that ultrahot Jupiters are ideal targets for atmospheric characterization studies using this framework, as we can measure the abundances of refractories, oxygen and carbon in the gas phase. Finally, we propose that hot Jupiters with silicate clouds and low water abundances might have accreted their envelopes between the soot line and the water snowline.

show abstract

Chemical Diversity in Protoplanetary Disks and Its Impact on the Formation History of Giant Planets

Cited by 41 publications

References 102 publications

Breaking Degeneracies in Formation Histories by Measuring Refractory Content in Gas Giants

Breaking Degeneracies in Formation Histories by Measuring Refractory Content in Gas Giants

Retrieving C and O Abundance of HR 8799 c by Combining High- and Low-resolution Data

Breaking Degeneracies in Formation Histories by Measuring Refractory Content in Gas Giants

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