From discs to planets: chemical constraints on planet formation

Tuesday 3 July, 09:30

The chemical composition of giant planet atmospheres provides a way to understand how and where they form by linking the planets to their formation environments. With ALMA now probing the chemical evolution of planet forming disc, understanding the link between different formation mechanisms and composition provides a powerful way to constrain planet formation. I will show that planet formation and chemical evolution are fundamentally linked, with different formation mechanisms producing different signatures in discs and planets. For example, volatiles frozen out into ices evolve differently under planetesimal accretion to pebble accretion. This is because the ices locked up into planetesimals remain in the cold outer disc, while pebbles migrate to the warmer regions of the inner disc, carrying their ices with them. These ices are then released into the gas as pebbles migrate across different snow lines. Thus pebble migration can chemically enrich the inner regions of discs. This leads to super-solar metallicity in giant planets that accrete their envelopes in the inner regions. The abundance patterns in these atmospheres contain fingerprints of metal-rich gas accretion, such as elevated C/O ratios, which cannot be created by accreting planetesimals. This allows the compositions of planet atmospheres to constrain the roles of pebble and planetesimal accretion in planet formation.

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