Predicting the potential growth of biomass on planetary bodies

An appropriate energy supply, whether perpetual or fleeting, is tantamount to the success of life in the Universe as we know it. Beyond 'chasing the water' or even 'chasing the kinetics', searching for signs of energetic availability could perhaps help pave the way to understand the limits for any theoretical living organism, be it an example of life 'as we know it' or otherwise. Few studies have been made into the energetic availability of different planetary environments as a limiter for potential biological activity.

The aim of this project is to build a computational model with the ability to quantify the available energy in a given environment, and use this information to estimate the extent to which a given - or hypothetical - microorganism could grow. This follows from recent studies into characterising microbial growth in Earth's hydrothermal vents. The model, focused on astrobiological applications, will allow for the study of a variety of unique physical and chemical environments and the exploration of whether they inhibit or bolster potential microbial growth rates. The energetic model will be built with extensibility in mind from existing thermochemical theory and redox chemistry in nonstandard conditions, with the scope to include environmental effects such as solvent flows, weathering or insolation and their influence on chemical kinetics. Environmental factors may also be considered when estimating how an organism could make use of the available energy, for example by considering biodegradation due to high temperatures or harsh radiation, and/or developing methods to quantify nutrient colimitation as a throttle to growth. For instance, abiotic factors such as the availability of P or S can provide a fundamental limit on the growth of microorganisms - and the proposed model may take steps to quantify their impact.

A number of potential candidates for testing the limits of the model are proposed, ranging from small scale, empirically measurable environments on the Earth to more ambitious astronomical simulations including the subsurface of Mars, oceans of Europa or Enceladus, and potentially even exoplanets on a global scale. The direction in which the model eventually takes depends on its final form; it may head down just one or two of these routes on a case-by-case basis considering particular environments in some depth, or focus on the broader picture.

The project will be primarily supervised by Professor C. S. Cockell, with Professor W. K. M. Rice as secondary supervisor.