Issue |
A&A
Volume 672, April 2023
|
|
---|---|---|
Article Number | A142 | |
Number of page(s) | 15 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361/202245592 | |
Published online | 14 April 2023 |
Circumplanetary disk ices
II. Composition
1
Kapteyn Astronomical Institute, University of Groningen,
PO Box 800, 9700 AV Groningen,
The Netherlands
e-mail: oberg@astro.rug.nl
2
Faculty of Aerospace Engineering, Delft University of Technology,
Kluyverweg 1, 2629 HS Delft,
The Netherlands
3
University of Leiden,
PO Box 9513, 2300 RA,
Leiden, The Netherlands
4
Max-Planck-Institut für extraterrestrische Physik,
Giessenbachstrasse 1,
85748
Garching, Germany
Received:
30
November
2022
Accepted:
6
February
2023
Context. The subsurface oceans of icy satellites are among the most compelling among the potentially habitable environments in our Solar System. The question of whether a liquid subsurface layer can be maintained over geological timescales depends on its chemical composition. The composition of icy satellites is linked to that of the circumplanetary disk (CPD) in which they form. The CPD accretes material from the surrounding circumstellar disk in the vicinity of the planet, however, the degree of chemical inheritance is unclear.
Aims. We aim to investigate the composition of ices in chemically reset or inherited circumplanetary disks to inform interior modeling and the interpretation of in situ measurements of icy solar system satellites, with an emphasis on the Galilean moon system.
Methods. We used the radiation-thermochemical code ProDiMo to produce circumplanetary disk models and then extract the ice composition from time-dependent chemistry, incorporating gas-phase and grain-surface reactions.
Results. The initial sublimation of ices during accretion may result in a CO2 -rich ice composition due to efficient OH formation at high gas densities. In the case of a Jovian CPD, the sublimation of accreted ices results in a CO2 iceline between the present-day orbits of Ganymede and Callisto. Sublimated ammonia ice is destroyed by background radiation while drifting towards the CPD midplane. Liberated nitrogen becomes locked in N2 due to efficient self-shielding, leaving ices depleted of ammonia. A significant ammonia ice component remains only when ices are inherited from the circumstellar disk.
Conclusions. The observed composition of the Galilean moons is consistent with the sublimation of ices during accretion onto the CPD. In this scenario, the Galilean moon ices are nitrogen-poor and CO2 on Callisto is endogenous and primordial. The ice composition is significantly altered after an initial reset of accreted circumstellar ice. The chemical history of the Galilean moons stands in contrast to the Saturnian system, where the composition of the moons corresponds more closely with the directly inherited circumstellar disk material.
Key words: planets and satellites: formation / planets and satellites: composition / astrochemistry / methods: numerical / protoplanetary disks
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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