Exoplanet atmosphere models often assume C/O > 1 and carbon-dominated chemistry (CO, CH4), but in planets with C/O < 0.8, the excess oxygen can favour silicon species such as SiO. This is relevant for interpreting transit spectra. A recent study addresses the formation and condensation of SiO in the absence of carbon using quantum chemistry simulations, which is beyond the scope of a Bachelor's thesis. However, the underlying phenomenon – the distribution of abundances among C, O, Si, and H species according to T, P, and C/O – can be studied with a much simpler thermodynamic equilibrium model.

What you gain

The student learns to formulate and numerically solve a system of chemical equilibrium equations (mass action law and element conservation) using tabulated equilibrium constants, and to interpret how the abundances of CO, SiO, SiO2, H2O, etc., change with temperature, pressure, and the C/O ratio. The contribution is to reproduce, on a small scale, the type of equilibrium abundance diagram that appears in the planetary atmospheric chemistry literature, not a new result.

What you need

Statistical physics and thermodynamics, numerical methods, Python (numpy, scipy.optimize for solving the non-linear equilibrium system). Thermodynamic constants (Gibbs free energies of formation) from public tables such as JANAF are needed, which the supervisor must provide or which are available in open literature.

Open data

Work plan

  1. Review of chemical equilibrium thermochemistry and articles on C-O-Si chemistry in planetary atmospheres40 h
  2. Model construction: relevant C, O, Si, H species, equilibrium constants, and conservation equations40 h
  3. Numerical implementation in Python (solving the non-linear system) and validation with known cases from the literature60 h
  4. Sweep across T, P, and C/O; identification of the region where SiO dominates over CO; comparison with real exoplanet parameters from the NASA catalogue40 h
  5. Writing the thesis and preparing the defence40 h

Do not take it if

This is not suitable if the supervisor cannot provide thermodynamic tables of Gibbs free energies of formation for the necessary species, or if the chemical equilibrium is expected to be coupled to a complete radiative transfer model (this exceeds the scope of a Bachelor's thesis); nor is it appropriate if the aim is to reproduce the electronic structure calculations or chemical kinetics of the original article.