Context
FUor-type accretion outbursts are powerful phenomena thought to occur multiple times in the lifetime of protoplanetary discs, including our own Solar Nebula. Yet, it remains unknown what is their impact on planet formation.
In particular, laboratory experiments found that icy pebbles may completely fall apart into micron-sized monomers if water ice sublimates. This may significantly hinder the process of planet formation.
What's been done
We built a state-of-the-art Monte Carlo coagulation code to follow the coagulation and fragmentation of compact and porous dust aggregates in a protoplanetary disc during and after a FUor-type accretion outburst. Unlike codes based on the Smoluchowski equation (e.g., DustPy), our code is able to follow the distribution of water ice amongst different particle sizes, such that condensation can be treated self-consistently.
Our paper in three key results
(1) If pebbles fall apart upon ice sublimation, it takes a significant time for pebbles to grow back and recover from the accretion outburst. This is much longer than the duration of FUor-type outbursts (~100 yr), meaning that the dust particle size may be use as a tracer of past outbursts in discs.
(2) If pebbles survive the ice sublimation process, the dust population maintains a broad range of sizes (micrometre to millimetre sizes). In that case, when water re-condenses after the accretion outburst, it results in a broad distribution of water ice content, with small grains taking most of the water ice reservoir. Pebbles remain water-poor for extensive durations, meaning that even long after the end of an accretion outburst, planetesimals would form dry in the protoplanetary disc.
(3) Thanks to our coagulation code, we present for the first time the process of collisional mixing , in which a population of dust particles with different composition gradually mix up and homogenize. This has much broader application, e.g., when considering the size-dependent temperature of dust grains resulting in multiple icelines.