Chemistry During the Gas-Rich Stage of Planet Formation

Bergin, Edwin A.; Cleeves, L. Ilsedore

doi:10.1007/978-3-319-55333-7_137

Cited by 11 publications

(8 citation statements)

References 143 publications

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“…While detailed chemical modeling is beyond the scope of the present paper, we examined the reaction rates from the existing Cleeves et al (2015) TW Hya chemical model with a dust surface area reduction of 85%. The latter is invoked to emulate the effects of dust settling and radial drift, which significantly reduce the effective solid surface for ice chemistry to occur (Hogerheijde et al 2011;Bergin & Cleeves 2018). In the layer where H 2 CO is abundant (z/R>0.25), the two gas-phase pathways with O and OH are far more efficient than CO-ice hydrogenation due to the warm temperatures of the surface layers.…”

Section: Gas-phase Versus Grain-surface Formation Of H 2 Comentioning

confidence: 99%

The TW Hya Rosetta Stone Project. II. Spatially Resolved Emission of Formaldehyde Hints at Low-temperature Gas-phase Formation

Scheltinga

Hogerheijde

Cleeves

et al. 2021

ApJ

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Formaldehyde (H 2 CO) is an important precursor to organics like methanol (CH 3 OH). It is important to understand the conditions that produce H 2 CO and prebiotic molecules during star and planet formation. H 2 CO possesses both gas-phase and solid-state formation pathways, involving either UV-produced radical precursors or CO ice and cold (20 K) dust grains. To understand which pathway dominates, gaseous H 2 COʼs ortho-to-para ratio (OPR) has been used as a probe, with a value of 3 indicating "warm" conditions and <3 linked to cold formation in the solid state. We present spatially resolved Atacama Large Millimeter/submillimeter Array observations of multiple ortho-and para-H 2 CO transitions in the TWHya protoplanetary disk to test H 2 CO formation theories during planet formation. We find disk-averaged rotational temperatures and column densities of 33±2 K, (1.1±0.1)× 10 12 cm −2 and 25±2 K, (4.4±0.3)×10 11 cm −2 for ortho-and para-H 2 CO, respectively, and an OPR of 2.49±0.23. A radially resolved analysis shows that the observed H 2 CO emits mostly at rotational temperatures of 30-40 K, corresponding to a layer with z/R0.25. The OPR is consistent with 3 within 60 au, the extent of the pebble disk, and decreases beyond 60 au to 2.0±0.5. The latter corresponds to a spin temperature of 12 K, well below the rotational temperature. The combination of relatively uniform emitting conditions, a radial gradient in the OPR, and recent laboratory experiments and theory on OPR ratios after sublimation, led us to speculate thatgas-phase formation is responsible for the observed H 2 CO across the TWHya disk.

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Section: Gas-phase Versus Grain-surface Formation Of H 2 Comentioning

confidence: 99%

The TW Hya Rosetta Stone Project. II. Spatially Resolved Emission of Formaldehyde Hints at Low-temperature Gas-phase Formation

Scheltinga

Hogerheijde

Cleeves

et al. 2021

ApJ

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“…Note that this also affects the total amount of water because O is locked up in CO. Given that other potential C-and N-bearing molecules are affected in a similar manner, mod-els of their condensation locations must consider kinetics and dynamical modelling, and it follows that the NH 3 , CH 3 OH, and H 2 O ice lines essentially coincided while CO and CH 4 condensed at much greater heliocentric distances (e.g., Dodson-Robinson et al 2009;Bergin and Cleeves 2018).…”

Section: Volatile Species and Their Condensation Fronts In The Protoplanetary Diskmentioning

confidence: 99%

The NC-CC Isotope Dichotomy: Implications for the Chemical and Isotopic Evolution of the Early Solar System

et al. 2020

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Understanding the formation of our planetary system requires identification of the materials from which it originated and the accretion processes that produced the planets. The compositional evolution of the solar system can be constrained by synthesizing astronomical datasets and numerical models with elemental and isotopic compositions from objects that directly sampled the disk: meteorites and their constituents (chondrules, refractory inclusions, and matrix). This contribution reviews constraints on early solar system evolution provided by the so-called non-carbonaceous (NC) and carbonaceous chondrite (CC) groups and their relationship to the volatile element characteristics of chondritic meteorites. In previous work, the NC or CC character of a parent body was used to infer its accretion location in the protoplanetary disk. The NC groups purportedly originated in the inner disk, and the CC groups were derived from the outer disk, where the NC and CC regions of the disk may have been separated early on by proto-Jupiter, a pressure maximum, or a dust trap in the disk. The tenet that all CC parent bodies accreted in the outer disk is, in part, based on evidence that a handful of CC meteorites are enriched in volatile species compared to NC meteorites. Here, it is reviewed if and how the volatile element and nucleosynthetic isotope compositions of meteorites can be linked to accretion locations within the disk. The nucleosynthetic isotope compositions of whole rock meteorite samples contrast the trends found for their major volatile element compositions (i.e., C, N, and O). Although there may be an increase in volatile abundances when comparing some stony NC and CC meteorites and their inferred accretion locations within the disk, this is not necessarily a general rule. The difficulties with inferring parent body accretion locations are discussed. It is found that it cannot always be assumed that parent bodies which formed in the CC reservoir are "volatile-rich" relative to those that formed in the NC reservoir which are "volatilepoor". Consequently, tracing the origin of terrestrial volatiles using the NC-CC isotope dichotomy remains challenging.

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“…Further, the midplane temperature controls the balance between gas-phase deposition and sublimation and thus the relative spatial composition of ices. For example, H 2 O freezes out at dust temperatures lower than ≈120-170 K (Fraser et al 2001;Bergin & Cleeves 2018), while CO freezes out below ∼21-25 K in TW Hya, (Bisschop et al 2006;Fayolle et al 2016;Schwarz et al 2016;Zhang et al 2017). Thus, the gas/ice transition or snowline for water and CO is set by the thermal structure with water close to the star and CO at greater distances.…”

Section: Introductionmentioning

confidence: 99%

The TW Hya Rosetta Stone Project. III. Resolving the Gaseous Thermal Profile of the Disk

Calahan¹,

Bergin²,

Zhang³

et al. 2021

ApJ

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The thermal structure of protoplanetary disks is a fundamental characteristic of the system that has wide-reaching effects on disk evolution and planet formation. In this study, we constrain the 2D thermal structure of the protoplanetary disk TW Hya structure utilizing images of seven CO lines. This includes new ALMA observations of 12 CO J = 2-1 and C 18 O J = 2-1 as well as archival ALMA observations of 12 CO J = 3-2, 13 CO J = 3-2 and 6-5, and C 18 O J = 3-2 and 6-5. Additionally, we reproduce a Herschel observation of the HD J = 1-0 line flux and the spectral energy distribution and utilize a recent quantification of CO radial depletion in TW Hya. These observations were modeled using the thermochemical code RAC2D, and our best-fit model reproduces all spatially resolved CO surface brightness profiles. The resulting thermal profile finds a disk mass of 0.025 M e and a thin upper layer of gas depleted of small dust with a thickness of ∼1.2% of the corresponding radius. Using our final thermal structure, we find that CO alone is not a viable mass tracer, as its abundance is degenerate with the total H 2 surface density. Different mass models can readily match the spatially resolved CO line profiles with disparate abundance assumptions. Mass determination requires additional knowledge, and, in this work, HD provides the additional constraint to derive the gas mass and support the inference of CO depletion in the TW Hya disk. Our final thermal structure confirms the use of HD as a powerful probe of protoplanetary disk mass. Additionally, the method laid out in this paper is an employable strategy for extraction of disk temperatures and masses in the future.

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Chemistry During the Gas-Rich Stage of Planet Formation

Cited by 11 publications

References 143 publications

The TW Hya Rosetta Stone Project. II. Spatially Resolved Emission of Formaldehyde Hints at Low-temperature Gas-phase Formation

The TW Hya Rosetta Stone Project. II. Spatially Resolved Emission of Formaldehyde Hints at Low-temperature Gas-phase Formation

The NC-CC Isotope Dichotomy: Implications for the Chemical and Isotopic Evolution of the Early Solar System

The TW Hya Rosetta Stone Project. III. Resolving the Gaseous Thermal Profile of the Disk

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