Harrison Nicholls / Research

↖ go up to Index

↓ jump to: Research projects, Tools and models

Preface

This page summarises my current and past research. While this journey has been continuous, I've tried to discretise it into separate projects for easier reading. These projects are listed here in chronological order, newest first.

Research projects

DPhil project

Rocky planet atmospheric chemistry

My current research is focussed on understanding the chemical evolution of the atmospheres of young rocky-planets. The relationship between the interior, the surface, the atmosphere, space is complex and is not something we yet understand the dynamics of. By combining various numerical models together we can trace out the evolution pathways of these planets, which is not only critical for interpreting observations, but can help elucidate their histories.

Oxford Physics profile

Self-consistent flares

Temperature-chemistry coupling in the evolution of gas giant atmospheres driven by stellar flares

The effect of enhanced UV irradiation associated with stellar flares on the atmospheric composition and temperature of gas giant exoplanets was investigated. This was done using a 1D radiative-convective-chemical model with self-consistent feedback between the temperature and the non-equilibrium chemistry.
It was found that flare-driven changes to chemical composition and temperature give rise to prolonged trends in evolution across a broad range of pressure levels and species. Allowing feedback between chemistry and temperature plays an important role in establishing the quiescent structure of these atmospheres, and determines their evolution due to flares. It was found that cooler planets are more susceptible to flares than warmer ones, seeing larger changes in composition and temperature, and that temperature-chemistry feedback modifies their evolution.
Long-term exposure to flares changes the transmission spectra of gas giant atmospheres; these changes differed when the temperature structure was allowed to evolve self-consistently with the chemistry. Changes in spectral features due to the effects of flares on these atmospheres can be associated with changes in composition. The effects of flares on the atmospheres of sufficiently cool planets will impact observations made with JWST. It is necessary to use self-consistent models of temperature and chemistry in order to accurately capture the effects of flares on features in the transmission spectra of cooler gas giants, but this depends heavily on the radiation environment of the planet.

Nicholls et al. (2023) in MNRAS and on arXiv.

Tools and models

PROTEUS

Framework for simulating the evolution of young rocky planets

PROTEUS is a Python framework that simulates the coupled evolution of the atmospheres and interiors of rocky planets. It makes use of various submodules, such as the VULCAN chemical-kinetics code and the SOCRATES radiative-transfer code.

Note that I do not lead the development of PROTEUS, although I have been significantly involved in its development.

View the PROTEUS GitHub page

ATMO

Radiative-convective photochemical kinetics model for gassy planets.

ATMO is a 1D model of the atmospheres of gas planets. It can evolve the chemistry of these planets over time using a photochemical kinetics model, as well as solve for equilibrium abundances. The headline feature of ATMO is that it can self-consistently solve for these atmospheres by re-adjusting the temperature profile to radiative-convective equilibrium while integrating the chemistry. The model can also generate transmission and emission spectra, and has been extensively used for retrievals. It's written in Fortran 90, and has been adapted for 2D modelling in some contexts.

Note that I did not lead the development of ATMO. My contributions to the code enabled some research, however the majority of the code had already existed for a long time before I came near it.

View the ATMO project website