Planets are forming in young star systems far faster than our models can explain. Observations show dust rings in discs only half a million years old, yet current simulations assume planet formation takes at least a million years—meaning our understanding of how dust grains clump into planet-building blocks is fundamentally incomplete. This fellowship will build new computer models that simulate what actually happens in these young, massive discs. Unlike existing models that assume settled, isolated discs, these simulations will account for gravitational instability—where the disc’s own gravity drives spiral arms that can concentrate dust into collapsing clumps. The work will also model “late infall,” the process where fresh gas from surrounding clouds falls onto the disc, altering its chemistry and structure. This could explain why different star systems end up with wildly different molecular compositions and exoplanet makeups. This is fundamental science. There is no immediate practical application for understanding how dust grains become planetesimals in young protoplanetary discs. But the results will provide the theoretical framework needed to interpret data from world-leading telescopes, potentially reshaping our picture of how planetary systems—including our own—come into being. Similar fundamental work on disc dynamics has previously informed models of how solar systems form, which underpins everything from exoplanet hunting to understanding Earth’s own origins.
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Protostars are born with dusty gas discs, as part of the star-forming process. Planets form within these protoplanetary discs through the gradual growth of solid dust particles into larger grains and then planetesimals, the building blocks of planets. Our current understanding suggests that planetesimal growth occurs over a timescale of around 1 million years. However, state-of-the-art observations reveal signs of planet formation such as dust rings in protoplanetary discs as young as 0.5 million years. This implies that planet formation begins far earlier than previously thought, probably as soon as the disc forms. Furthermore, we also observe some discs pulling in material from nearby gas clouds, a process known as late infall, meaning that protoplanetary discs do not evolve in isolation as our models assume. My fellowship will deliver the tools and predictions appropriate for the emerging paradigms that planet formation starts early in the lifetime of a protoplanetary disc and that late infall can occur, altering the planet-forming environment. Current models are inadequate for simulating the young discs in which planet formation must begin because they typically consider more evolved, settled discs. Young discs are over 10 times more massive and are therefore susceptible to the gravitational instability (GI) because the self-gravity of the disc becomes significant. The GI drives spiral arms, heats the disc and may cause the disc to fragment. Solid particles may clump in the spiral arms and these clumps may grow massive enough to gravitationally collapse, accelerating the growth of planetesimals. The local dust properties are closely linked to the cooling rate. This might provide a feedback mechanism to stabilize dust clumps against gravitational collapse and allow them to grow more massive. My primary goal is to develop disc simulations that link the thermal processes to the dust evolution for the first time. I will then simulate how dust clumps evolve in young discs to explore how the first planetesimals form. A further aim is to study how late infall changes the structure of the disc, and for how long, so that we can construct models to explore how ongoing planet formation is affected. I will also test how the addition of fresh interstellar gas to the evolved disc material alters the raw materials available for forming planets by modelling the chemical evolution. The results could explain the poorly understood diversity in the distribution of molecules among observed discs and the wide variation in the makeup of exoplanet systems. Alongside my research, I will develop and deliver Encounter Physics, a programme to link up year 10 widening participation students with physics university students and researchers (the physicists) to encourage the uptake of A Level physics among young people from disadvantaged backgrounds. For each school and cohort, the physicists will discuss their work, study, and life as a scientist with the same small groups of students over 4 visits. This will forge a connection between students and 'real' physicists to help year 10 students picture themselves studying physics. This fellowship will fill gaps in our understanding of the processes acting in protoplanetary discs by developing models for little-studied scenarios that we now expect to shape planetary systems. My results will provide the theoretical basis that we currently lack for interpreting observations of young discs and unlock the potential of the latest data from world-leading telescope facilities.
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