The Molecular Composition of Shadowed Proto-solar Disk Midplanes Beyond the Water Snowline

• Published in: The Astrophysical journal 2022-09, Vol.936 (2), p.188
• Main Authors: Notsu, Shota, Ohno, Kazumasa, Ueda, Takahiro, Walsh, Catherine, Eistrup, Christian, Nomura, Hideko
• Format: Article
• Language: English
• Subjects: Accretion disks; Ammonia; Astrochemistry; Astrophysics; Carbon dioxide; Chemical composition; Chemical reactions; Depletion; Dust; Exoplanet atmospheres; Grains; Hydrocarbons; Ice; Ice formation; Interstellar abundances; Interstellar molecules; Jupiter; Nitrogen; Organic chemistry; Oxygen; Planet formation; Planetary atmospheres; Planetary system formation; Protoplanetary disks; Saturated hydrocarbons; Shadows; Snowline; Tracers; Volatile compounds
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac87fa

The disk midplane temperature is potentially affected by the dust traps/rings. The dust depletion beyond the water snowline will cast a shadow. In this study, we adopt a detailed gas-grain chemical reaction network, and investigate the radial gas and ice abundance distributions of dominant carbon-, oxygen-, and nitrogen-bearing molecules in disks with shadow structures beyond the water snowline around a proto-solar-like star. In shadowed disks, the dust grains at r ∼ 3–8 au are predicted to have more than ∼5–10 times the amount of ices of organic molecules such as H 2 CO, CH 3 OH, and NH 2 CHO, saturated hydrocarbon ices such as CH 4 and C 2 H 6 , in addition to H 2 O, CO, CO 2 , NH 3 , N 2 , and HCN ices, compared with those in non-shadowed disks. In the shadowed regions, we find that hydrogenation (especially of CO ice) is the dominant formation mechanism of complex organic molecules. The gas-phase N/O ratios show much larger spatial variations than the gas-phase C/O ratios; thus, the N/O ratio is predicted to be a useful tracer of the shadowed region. N 2 H + line emission is a potential tracer of the shadowed region. We conclude that a shadowed region allows for the recondensation of key volatiles onto dust grains, provides a region of chemical enrichment of ices that is much closer to the star than within a non-shadowed disk, and may explain to some degree the trapping of O 2 ice in dust grains that formed comet 67P/Churyumov-Gerasimenko. We discuss that, if formed in a shadowed disk, Jupiter does not need to have migrated vast distances.