2025/08/08 by Jenny K. Calahan, Calahan, Jenny K., Karin Öberg +3
Chemistry · Physics and Astronomy · #Astrophysics and Star Formation Studies #Earth and Planetary Astrophysics (astro-ph.EP) #Electrical and Electromagnetic Research #FOS: Physical sciences #Fullerene Chemistry and Applications #Solar and Stellar Astrophysics (astro-ph.SR)
paper · pdf · doi:10.48550/arxiv.2508.06613
openalex publication_date 2025/08/08 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The vast majority of young stars hosting planet-forming disks exist within clustered environments, like the Orion Nebula, implying that seemingly `extreme' UV environments (104 G0 and above) are not so atypical in the context of planet formation. Using thermo-chemical modeling, we explore how the temperature and chemistry within a protoplanetary disk around a T Tauri star is impacted by the surrounding UV environment. The disk becomes hotter due to heating by photodissociation of molecules, photoelectric heating, H2, and atomic processes and as a result the area in which molecules exist in the ice-phase shrinks, being pushed both downward and inward. Beyond 1AU the chemistry changes most significantly in a UV-rich background; the atmosphere becomes more H2O, OH, and atomic-rich. Hydrocarbons, however, reside primarily well within 1AU of the disk, thus their abundance and distribution is not impacted by the UV field, up to a 106 G0. The products of photodissociation and photochemistry are formed deeper into the disk with increasing UV background field strength beyond 1AU, impacting the chemistry near the midplane. Effectively a `reset' chemistry takes place, with an enhancement of atoms, simple molecules, and molecules in the gas-phase. Planets that form in highly irradiated regions will be exposed to a different chemical reservoir in the gas and ice-phases than that in an isolated disk, and the impact from the UV background should only be detectable in highly irradiated disks (~106 G0).