Astrochemistry and compositions of planetary systems

Öberg, Karin I.; Bergin, Edwin A.

doi:10.1016/j.physrep.2020.09.004

Cited by 194 publications

(165 citation statements)

References 452 publications

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“…The composition of dust grains in protoplanetary disks is a topic of active research (see recent review by Oberg & Bergin 2020). We adopt the grain composition prescribed in the DSHARP survey papers and use the publicly available tools generously provided by the survey team for the calculation of grain properties (Birnstiel et al 2018).…”

Section: Calculation Of Dust Opacitymentioning

confidence: 99%

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

Chachan

Lee

Knutson

2021

ApJ

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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 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 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.

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Section: Calculation Of Dust Opacitymentioning

confidence: 99%

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

Chachan

Lee

Knutson

2021

ApJ

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“…Protoplanetary disks around young stars are the cradles of planets, and the chemical composition in these disks sets the exoplanet atmospheric composition and the formation of prebiotic molecules on their surfaces (Ehrenfreund & Charnley 2000;Öberg & Bergin 2021). So far, mostly simple molecules have been detected in disks (e.g.…”

Section: Introductionmentioning

confidence: 99%

A major asymmetric ice trap in a planet-forming disk

Marel

Booth

Leemker

et al. 2021

A&A

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Context. The chemistry of planet-forming disks sets the exoplanet atmosphere composition and the prebiotic molecular content. Dust traps are of particular importance as pebble growth and transport are crucial for setting the chemistry where giant planets form. Aims. The asymmetric Oph IRS 48 dust trap located at 60 au radius provides a unique laboratory for studying chemistry in pebbleconcentrated environments in warm Herbig disks with gas-to-dust ratios as low as 0.01. Methods. We use deep ALMA Band 7 line observations to search the IRS 48 disk for H 2 CO and CH 3 OH line emission, the first steps of complex organic chemistry. Results. We report the detection of seven H 2 CO and six CH 3 OH lines with energy levels between 17 and 260 K. The line emission shows a crescent morphology, similar to the dust continuum, suggesting that the icy pebbles play an important role in the delivery of these molecules. Rotational diagrams and line ratios indicate that both molecules originate from warm molecular regions in the disk with temperatures >100 K and column densities ∼ 10 14 cm −2 or a fractional abundance of ∼ 10 −8 and with H 2 CO/CH 3 OH∼0.2, indicative of ice chemistry. Based on arguments from a physical-chemical model with low gas-to-dust ratios, we propose a scenario where the dust trap provides a huge icy grain reservoir in the disk midplane, or an 'ice trap', which can result in high gas-phase abundances of warm complex organic molecules through efficient vertical mixing. Conclusions. This is the first time that complex organic molecules have been clearly linked to the presence of a dust trap. These results demonstrate the importance of including dust evolution and vertical transport in chemical disk models as icy dust concentrations provide important reservoirs for complex organic chemistry in disks.

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“… 20 and references therein), and the dust and volatile gas structure and composition of protoplanetary disks (ref. 21 and references therein), including interactions of the disk with gas- or ice-giant protoplanets. However, only limited astronomical observations can be made about conversion of disk materials (gas, dust, and pebbles) to planets in other solar systems.…”

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confidence: 99%

Early volatile depletion on planetesimals inferred from C–S systematics of iron meteorite parent bodies

Hirschmann

Bergin

Blake

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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During the formation of terrestrial planets, volatile loss may occur through nebular processing, planetesimal differentiation, and planetary accretion. We investigate iron meteorites as an archive of volatile loss during planetesimal processing. The carbon contents of the parent bodies of magmatic iron meteorites are reconstructed by thermodynamic modeling. Calculated solid/molten alloy partitioning of C increases greatly with liquid S concentration, and inferred parent body C concentrations range from 0.0004 to 0.11 wt%. Parent bodies fall into two compositional clusters characterized by cores with medium and low C/S. Both of these require significant planetesimal degassing, as metamorphic devolatilization on chondrite-like precursors is insufficient to account for their C depletions. Planetesimal core formation models, ranging from closed-system extraction to degassing of a wholly molten body, show that significant open-system silicate melting and volatile loss are required to match medium and low C/S parent body core compositions. Greater depletion in C relative to S is the hallmark of silicate degassing, indicating that parent body core compositions record processes that affect composite silicate/iron planetesimals. Degassing of bare cores stripped of their silicate mantles would deplete S with negligible C loss and could not account for inferred parent body core compositions. Devolatilization during small-body differentiation is thus a key process in shaping the volatile inventory of terrestrial planets derived from planetesimals and planetary embryos.

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Astrochemistry and compositions of planetary systems

Cited by 194 publications

References 452 publications

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

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

A major asymmetric ice trap in a planet-forming disk

Early volatile depletion on planetesimals inferred from C–S systematics of iron meteorite parent bodies

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