SPONCHpop: Tracing Planet Formation Histories with Atmospheric Sulphur

The elemental composition of exoplanetary atmospheres provides a unique opportunity to investigate the formation and evolutionary history of giant planets. While carbon- and oxygen-bearing species have traditionally been used to constrain formation pathways, sulphur chemistry remains comparatively unexplored despite its sensitivity to planetary accretion history, formation location, and atmospheric evolution. In this work, we investigate the potential of atmospheric sulphur abundances as tracers of planet formation histories across a diverse population of giant exoplanets.

Using synthetic planet populations generated with the SPONCHpop framework at University College London together with atmospheric forward modelling and retrievals using TauREx 3, we investigate the detectability of atmospheric sulphur abundances across diverse formation environments, migration pathways, and planetary temperatures. Our study includes both highly irradiated hot Jupiters and colder giant planets spanning a wide range of masses, sulphur abundances, and orbital separations (See the picture down below). We assess the recoverability of sulphur-bearing species under realistic observational conditions expected from the upcoming Ariel mission.

Our first results show that the uncertainty in sulphur abundance strongly decreases with increasing signal-to-noise ratio (SNR), with precisions of ~0.2 dex typically achievable at SNR ≈ 20–40, while ~0.1 dex generally requires SNR ≳ 40–60 depending on planetary properties. Sulphur retrieval is most successful for hotter, larger planets with extended atmospheres, whereas cooler planets require substantially higher SNR to reach comparable precision.

Our results demonstrate that sulphur abundances can provide complementary constraints on giant planet formation and migration histories beyond traditional diagnostics such as metallicity and C/O ratios. In particular, sulphur-bearing species may help distinguish planets formed in chemically distinct regions of the protoplanetary disc and provide new insight into volatile accretion and atmospheric evolution.

Figure: Selected planets (coloured and open circles; 100 out of ∼ 2 500 objects) from the viscous irradiated disc model with pratio = 0.5. Grey
circles show the full simulated population. Open circles denote planets with S/H = 0 (Somerville-Thomas et al. 2026). The dashed horizontal line
indicates the mass of Jupiter, whose orbital distance is marked by the Jupiter symbol (Wong et al. 2004).).