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Tracking volatile CHNOS on non-local dust particles during the first stage of planet formation with SHAMPOO

Presentation #500.02 in the session Origin of Planetary Systems (Oral Presentation)

Published onOct 23, 2023
Tracking volatile CHNOS on non-local dust particles during the first stage of planet formation with SHAMPOO

The composition and structure of planets crucially depend on the amount of carbon, hydrogen, nitrogen, oxygen and sulfur (CHNOS) inherited from their formation. During planet formation, large amounts of CHNOS are stored as ices (e.g. H2O, CO, CO2, NH3, SO2, OCS) on the dust grains present in planet-forming disks. The evolution of the amount of volatile ices, however, is affected by disk processes comprising dynamical transport, collisional growth and fragmentation and the adsorption and desorption of ice. These processes can be highly coupled and non-local. Moreover, the adsorption and desorption of ice can be affected by the physical properties of the dust, such as filling factor and fragmentation velocity (fragility).

We introduce the SHAMPOO (StocHAstic Monomer PrOcessOr) code as a novel method for tracking the influence of non-local disk processes on the ices on dust grains. We here track the effects of dynamical, collisional and ice processing on the volatile CHNOS budget of a single tracer particle referred to as a “monomer”, which effectively represents a unit of mass. This monomer is usually embedded in a much larger dust aggregate, which can change size due to collisional processing. Inferences about the behavior of local dust populations can be made by averaging over the evolutionary trajectories of many monomers.

Local simulations of monomers at 10 AU reveal that monomers embedded in smaller, more fragile, aggregates with fragmentation velocities of 1 m/s undergo adsorption and photodesorption more frequently than monomers in aggregates with fragmentation velocities of 5 and 10 m/s. We also find that at 10 AU in the midplane, aggregates with a very low filling factor (ϕ = 1e−3) are able to accumulate ice 22 times faster on average than solid aggregates (ϕ = 1) under identical conditions. In addition, we track many (>10 000) monomers from randomly determined initial positions under the influence of non-local disk processing. Throughout a significant portion of the planet-forming disk, local dust populations were found to consist of a mix of monomers from considerably differing initial positions.

We conclude that the processing of ice does not remain limited to dust aggregate surfaces if the aggregate is either fragile (low fragmentation velocity) or very porous (low filling factor). Furthermore, non-local disk processing can have a significant effect on the volatile CHNOS budgets of dust at the onset of planet formation.

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