Saturn's Formation at the Carbon Dioxide Iceline
Abstract
Saturn's bulk metallicity and atmospheric volatile enrichments exceed those of Jupiter. Combined with their similar heavy-element masses, this suggests that Saturn formed farther out in a protoplanetary disk whose metallicity increased with heliocentric distance. Numerous models argue that Jupiter formed near the H2O iceline; Saturn's composition is therefore expected to reflect accretion beyond this region. We test whether Saturn's elemental enrichments can be reproduced by formation near the CO2 or CO icelines using a one-dimensional viscous α-disk model that tracks the transport, sublimation, and recondensation of 13 volatile carriers. We compute time-dependent radial distributions of solids and vapors for α= 5×10−4--5×10−3 and varied CO/CO2 abundance ratios, and compare the resulting metallicities and enrichments with Saturn's observed composition. Strong carbon and oxygen enrichment peaks result from the cold-finger effect, most prominently at the CO2 iceline, where supersolar metallicities comparable to Saturn's envelope are achieved only for α≤ 10−3. Smaller C and O enrichment peaks also occur at the CO iceline, but the local protosolar nebula metallicity there never reaches Saturn's inferred value. At ∼0.2--0.3 Myr, carbon and phosphorus enrichments in this region match Saturn's atmospheric values, while noble-gas abundances remain near protosolar owing to their long diffusion times. These results identify material originating near the CO2 iceline as the most likely source of Saturn's heavy-element inventory. For the conditions adopted in our model, our results imply that Saturn accreted this material early (≲0.3 Myr), in a weakly turbulent disk (α≲10−3) with a CO2-rich volatile inventory.
Related
- A Clearer View of HAT-P-1 b: JWST NIRSpec G395H Reveals Water, Carbon Dioxide, and Possibly Hydrogen Sulfide
- A Clearer View of HAT-P-1 b: JWST NIRSpec G395H Reveals Water, Carbon Dioxide, and Possibly Hydrogen Sulfide
- The formation of silicon-carbon chain molecules in IRC+10216
- The formation of silicon-carbon chain molecules in IRC+10216
- Extending the theory of figures to cylindrical rotation: Implications for Saturn’s interior
BibTeX
@misc{aguichine2026saturns,
title = {{Saturn's Formation at the Carbon Dioxide Iceline}},
author = {Artyom Aguichine and Olivier Mousis and Robin M. Canup},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.33257},
eprint = {2610.33257},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.33257},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Saturn's Formation at the Carbon Dioxide Iceline
AU - Artyom Aguichine
AU - Olivier Mousis
AU - Robin M. Canup
PY - 2026
DA - 2026/10/23
PB - arXiv
DO - 10.48550/arxiv.2610.33257
UR - https://arxiv.org/abs/2610.33257
AB - Saturn's bulk metallicity and atmospheric volatile enrichments exceed those of Jupiter. Combined with their similar heavy-element masses, this suggests that Saturn formed farther out in a protoplanetary disk whose metallicity increased with heliocentric distance. Numerous models argue that Jupiter formed near the H_2O iceline; Saturn's composition is therefore expected to reflect accretion beyond this region. We test whether Saturn's elemental enrichments can be reproduced by formation near the CO_2 or CO icelines using a one-dimensional viscous α-disk model that tracks the transport, sublimation, and recondensation of 13 volatile carriers. We compute time-dependent radial distributions of solids and vapors for α= 5×10^−4--5×10^−3 and varied CO/CO_2 abundance ratios, and compare the resulting metallicities and enrichments with Saturn's observed composition. Strong carbon and oxygen enrichment peaks result from the cold-finger effect, most prominently at the CO_2 iceline, where supersolar metallicities comparable to Saturn's envelope are achieved only for α≤ 10^−3. Smaller C and O enrichment peaks also occur at the CO iceline, but the local protosolar nebula metallicity there never reaches Saturn's inferred value. At ∼0.2--0.3 Myr, carbon and phosphorus enrichments in this region match Saturn's atmospheric values, while noble-gas abundances remain near protosolar owing to their long diffusion times. These results identify material originating near the CO_2 iceline as the most likely source of Saturn's heavy-element inventory. For the conditions adopted in our model, our results imply that Saturn accreted this material early (≲0.3 Myr), in a weakly turbulent disk (α≲10^−3) with a CO_2-rich volatile inventory.
ER -