The Origins Of Planets For ArieL (OPAL) Key Science Project: The End-to-end Planet Formation Campaign For The ESA Space Mission Ariel

The growing body of atmospheric observations of exoplanets from space and ground-based facilities showcases how the great diversity of the planetary population is not limited to their physical properties but extends to their compositions.

The ESA space mission Ariel will observe and characterise hundreds of exoplanetary atmospheres to explore and understand the roots of this compositional diversity. To lay the foundations for the Ariel mission, the OPAL Key Science Project is tasked with creating an unprecedented library of realistic synthetic atmospheres spanning tens of elements and hundreds of molecules on which the Ariel consortium will test and validate its codes and pipelines ahead of launch.

In this work we describe the aims and the pipeline of codes of the OPAL project, as well as the process through which we trace the genetic link connecting planets to their native protoplanetary disks and host stars.

We present the early results of this complex and unprecedented endeavour and discuss how they highlight the great diversity of outcomes that emerge from the large degeneracy in the parameter space of possible initial conditions to the planet formation process.

This, in turn, illustrates the growing importance of interdisciplinary modelling studies supported by high-performance computing methods and infrastructures to properly investigate this class of high-dimensionality problems.

Evolutionary tracks of the elemental ratios over 3 Myr across all considered scenarios. Ratios are shown in pairs across four key compositional regions: within the H₂O snowline (region 1, top-left), between the H₂O and CO₂ snowlines (region 2, top-right), between the CO₂ and CH₄ snowlines (region 3, bottom-left), and beyond the CH₄ snowline (region 4, bottom-right). Values represent gas-phase elemental ratios, calculated from total elemental abundances averaged over the radial extent of each region and weighted by the surface density of the gas. The colour bars indicate the four chemical scenarios, with time progressing from lighter to darker shades. The three different markers represent the selected grain sizes and are placed along each track every 2×10⁵ yr. The dark marker on each track denotes 1 Myr. Dashed grey lines highlight regions of the parameter space where pairwise comparisons of the elemental ratios provide constraints on specific scenarios or subsets of scenarios. Reproduced with permission from Pacetti et al. (2025). — astro-ph.EP

Danae Polychroni, Diego Turrini, Romolo Politi, Sergio Fonte, Eugenio Schisano, Elenia Pacetti, Paolo Matteo Simonetti, Michele Zusi, Sergio Molinari, Stavro Ivanovski

Comments: 14 pages, 10 figures. Accepted for publication in Astronomy and Computing
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Computational Physics (physics.comp-ph)
Cite as: arXiv:2601.16841 [astro-ph.EP] (or arXiv:2601.16841v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2601.16841
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Submission history
From: Danae Polychroni
[v1] Fri, 23 Jan 2026 15:43:01 UTC (5,976 KB)
https://arxiv.org/abs/2601.16841

Astrobiology,