skip to content

Constraining the cometary delivery of prebiotic molecules to the terrestrial planets
Lead supervisor: Catriona McDonald, Institute of Astronomy
Co-supervisors: Richard Anslow, Institute of Astronomy; Amy Bonsor, Institute of Astronomy; Paul Rimmer, Cavendish Laboratory


Research proposal

A scenario which has long been implicated in the origins of life on Earth is the delivery of prebiotic feedstock molecules via cometary impacts (Oró 1961). Previous work suggests that significant quantities of prebiotic molecules are only able to survive the violent impact process inside small comets with low impact velocities (Pierazzo & Chyba 1999). During the late stages of planet formation, the terrestrial planets experienced a prolonged period of impacts by comets, scattered into the inner Solar System by the giant planets.  

Uncertainties remain regarding the detailed dynamical history of the solar system which drives cometary impacts. Thus, there remains questions about how the inventory of prebiotic molecules delivered by cometary impacts differs amongst the terrestrial planets.  

The student will work with Richard Anslow and Catriona McDonald to produce a simulated chronology of cometary impacts onto the terrestrial planets using a Monte Carlo-type approach. The student will consider multiple models of the solar system’s dynamical history to determine when cometary delivery may have been possible for the early-Earth which will constrain the global environmental conditions relevant for the emergence and development of life (e.g., Nesvorny et al. 2023).  This will involve combining observed comet size-frequency distributions with an impact velocity distribution which the student can determine either numerically or analytically depending on their interests (e.g., Nesvorny et al. 2017, Anslow et al. 2023).  

Using previous studies in the literature (e.g., Todd & Öberg 2020), and ongoing research from Richard Anslow and Catriona McDonald on the physical processes related with cometary impacts, the student will determine a set of criteria required for an impact to successfully deliver prebiotic molecules. The criteria will involve the comet’s size, composition and impact velocity and angle. The overall inventory of prebiotic molecules successfully delivered to the early-Earth under different solar system histories can then be determined, informing the relative feasibility of cometary delivery. Further, this project will investigate how this conclusion will change for the other terrestrial planets in the solar system, Mars and Venus, which have different bulk, and orbital parameters to the Earth. 

Relevant expertise 

Richard Anslow, Catriona McDonald and Amy Bonsor all have expertise in the dynamics of small bodies in planetary systems. Catriona McDonald has expertise in the physics of cometary impacts, using 3D simulations of oblique cometary impacts, and modelling the survival of prebiotic molecules. Richard Anslow has expertise in simulating the dynamics of comet impacts, and is currently using the lunar crater record to constrain cometary impact scenarios on the early-Earth. Paul Rimmer has expertise in the chemical networks relevant for the survival of prebiotic molecules. 


  1. Oró 1961, Nature
  2. Pierazzo & Chyba 1999, Meteoritics & Planetary Science 
  3. Nesvorny et al. 2023, Icarus 
  4. Nesvorny et al. 2017, The Astrophysical Journal 
  5. Anslow, Bonsor & Rimmer 2023, Proc. R. Soc. A 
  6. Todd & Öberg 2020, Astrobiology