My research interests cover a wide range of topics, but the primary theme that unites them is a desire to understand the formation and evolution of planets and the systems in which they reside. The bulk of my work is theoretical in nature, making use of mathematical models and computer simulations, but I try to maintain a narrow divide between my theoretical work and observational or experimental data.

Debris and debris disks

A common thread that runs through many of my research projects is debris, the leftover flotsam and jetsam of planet formation. Though much less flashy than their planetary cousins these small, sometimes under-appreciated, bodies have an important role to play in helping us piece together the processes of planet formation, both in our own Solar system and farther afield.

Perhaps the most obvious manifestation of this is my work on circumstellar debris disks. Although an individual piece of debris is much smaller than a planet, these small bodies have a very much larger surface area-to-mass ratio which means that a disk of debris can be much more easily detectable than a planet that is several orders of magnitude more massive, in much the same way that if you blow even a small amount of flour or chalk dust into the air it can make it hard to see through. This allows us to build up a picture of the population of planetary systems in ways that is not possible with planets themselves. Moreover, large and/or nearby disks can be spatially resolved allowing us to use the structure of the disk to make inferences about the presence of planets in the system.

Giant impacts

A major topic that has been part of many aspects of my research is giant impacts. Giant impacts occur in the chaotic final stages of terrestrial planet formation when massive planetary bodies collide with one other to form the final terrestrial planets. These are some of the most violent events to occur during the planet formation process and can strongly influence the final makeup of terrestrial planets, both in terms of their mass and in terms of the proportions of elements and minerals of which they are composed. As a result of the violence of these giant impacts, in addition to producing the final planets large quantities of small debris is also released. Although giant impacts are most associated with the formation of terrestrial planets they can also occur in other parts of a planetary system. The formation of the Pluto-Charon system is most likely the result of a giant impact.

Interstellar objects

Since the discovery of 'Oumuamua in 2017 I have been fascinated by interstellar objects. These are pieces of debris from other planetary systems and provide us with the means to investigate the formation and evolution of another planetary system in more direct and detailed ways than we can achieve with our indirect observations of distant systems. Although 'Oumuamua was not discovered until after its closest approach to Earth we could for example envisage sending a space mission to a future object and possibly capturing samples of it.


Many of these topics are represented in the projects listed on the projects page, in addition major ambitions for the future include improving our knowledge of the size distribution of debris produced in impacts as this is a significant issue for all debris studies, and reducing our reliance on computationally intensive N-body simulations.

In the past I have also studied the evaporation of planetary atmospheres under the influence of high-energy radiation, and maintain an interest in the physics of planetary atmospheres and their evolution.

For more detail about individual projects please see the Projects page.


  • Debris and debris disks
  • Giant impacts
  • Interstellar objects
  • Formation and evolution of planetary systems
  • Formation and evolution of individual planets, their surfaces and interiors
  • Planetary atmospheres

Image credit: Alan Jackson, summit of Mauna Kea looking towards the Keck and Subaru telescopes from the Gemini North telescope.