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Do Prebiotic Molecules Survive Cometary Impact?
Lead supervisor: Paul B Rimmer, Cavendish Laboratory
Co-supervisor: Sai Murali, Cavendish Laboratory; Catriona McDonald, Institute of Astronomy; Amy Bonsor, Institute of Astronomy


Research proposal

Context: Cometary delivery has been proposed as a source of molecules that can facilitate life’s origins (Chyba et al. 1990). Recent calculations have suggested very little cometary material would survive delivery to Earth (Todd & Öberg 2020) or other planets (Anslow et al. 2023). However, experiments find that some prebiotic molecules, like glycolaldehyde, could survive impacts (Zellner et al. 2020). These experiments have not been run under conditions appropriate to comets. Specifically, they were run without water. Performing experiments for a larger set of molecules, with and without water, will be needed to provide empirical insight into what prebiotic chemistry is likely to be delivered by cometary impacts.

Objectives: Working with Murali & Rimmer, the student will experimentally determine the thermal stability of three compounds important for prebiotic chemistry: ferrocyanide, glycine and glycolaldehyde. Then, working with McDonald, Bonsor & Rimmer, the student will apply their experimental results to a computational model of a cometary impact.

Methodology: The student will investigate thermal stability of three different samples: ferrocyanide, glycine and glycolaldehyde, with and without water. For each sample, the student will place the sample in a sealed Argon-filled container with an empty balloon attached to the top to allow for gas expansion. In one case, the sample will be placed in dry, in the other with Argon-degassed water. The samples will be held at different temperatures for varying amounts of time. The sample will be cooled and analyzed using NMR and UV-Vis spectra to determine the surviving concentrations. In this way, the student will determine the temperature-dependent lifetimes of these molecules, with and without water. Cometary impact models that predict the comet’s impact temperature as a function of time can incorporate these timescales to predict how much of the molecule initially in the comet is expected to survive and be delivered to the surface of a planet.

Expected Outcome: Measurement of the lifetimes, activation energies and surviving concentrations of delivered material, applicable for a wide range of planetary conditions. The predicted lifetime of dry ferrocyanide at low temperature could provide insights into what traces of prebiotic chemistry are expected to have survived on the surface of Mars.

Relevant Expertise: Dr. Rimmer is expert in chemical kinetics experiments and models, and in origins research. Dr. Bonsor is expert in the dynamics of solar systems and the physics and chemistry of interplanetary material. Dr. Murali is expert in physical organic chemistry. Dr. McDonald is expert in computational models of cometary impacts.


  • Anslow, Bonsor & Rimmer 2023. Can comets deliver prebiotic molecules to rocky exoplanets?. Proceedings of the Royal Society A, 479(2279), 20230434.
  • Chyba et al. 1990. Cometary delivery of organic molecules to the early Earth. Science, 249(4967), 366-373.
  • Todd & Öberg 2020. Cometary delivery of hydrogen cyanide to the early Earth. Astrobiology, 20(9), 1109-1120.
  • Zellner, McCaffrey, & Butler 2020. Cometary glycolaldehyde as a source of pre-RNA molecules. Astrobiology, 20(11), 1377-1388.