Jupiter’s “Cold” Formation in Protosolar Disk Shadow: An Explanation for the Planet’s Uniformly Enriched Atmosphere

Atmospheric compositions offer valuable clues to planetary formation and evolution. Jupiter has been the most well-studied giant planet in terms of its atmosphere; however, the origin of the Jovian atmospheric composition remains a puzzle as the abundances of highly volatile elements, such as nitrogen and noble gases, are comparable to those of other elements. Such uniform atmospheric enrichment could only originate from extremely cold environments. In this study, we propose a novel idea for explaining the Jovian atmospheric composition: dust pileup at the H₂O snow line casted a shadow and cooled the past Jupiter orbit. Planetesimals or a core formed in the cold shadowed region could enrich highly volatile elements as much as other elements through their dissolution in the envelope. We compute the temperature structure of a shadowed protosolar disk using a Monte Caro radiative transfer model of RADMC-3D. Then, we investigate the radial volatile distributions and predict the atmospheric composition of Jupiter with condensation calculations. We find that the vicinity of the current Jupiter orbit, approximately 3−7 AU, could be as cold as <30 K if the small-dust surface density varies by a factor of >30 across the H₂O snow line. Then, the shadow can cause the condensation of most volatile substances, namely N₂ and Ar. We demonstrate that the dissolution of shadowed solids can explain the elemental abundance patterns of the Jovian atmosphere even if proto-Jupiter was formed near Jupiter’s current orbit. The disk shadow may play a vital role in controlling atmospheric compositions. Thus, the effect of the shadow impacts the interpretation of upcoming observations of exoplanetary atmospheres by JWST.