Ice inheritance in dynamical disk models

TL;DR

This paper models how interstellar ices survive or are destroyed in protoplanetary disks, suggesting that icy planetesimals inherit pristine material mainly through pebble drift from outer disk regions, impacting organic delivery to planets.

Contribution

It introduces a realistic disk physics model for tracking interstellar ice destruction and inheritance pathways, emphasizing pebble drift as a key mechanism.

Findings

Small grains in the inner disk rapidly lose ices.

Pebbles formed at large radii can carry preserved ices inward.

Complex organics can survive disk passage intact.

Abstract

The compositions of planet-forming disks are set by a combination of material inherited from the interstellar medium and material reprocessed during disk formation and evolution. Indeed, comets and primitive meteorites exhibit interstellar-like isotopic ratios and/or volatile compositions, supporting that some pristine material was incorporated intact into icy planetesimals in the Solar Nebula. To date, the survival of volatile interstellar material in the disk stage has not been modeled using realistic disk physics. Here, we present a modeling framework to track the destruction of interstellar ices on dust grains undergoing transport processes within a disk, with a particular focus on explaining the incorporation of pristine material into icy planetesimals. We find it is difficult to explain inheritance through the local assembly of comets, as ice destruction is rapid for small (<10um) grains in the inner few tens of au. Instead, a plausible pathway to inheritance is to form pebbles at larger disk radii, which then drift inwards to the comet-forming zone with their ices mostly preserved. Small grains beyond ~100 au can experience ice photodissociation at the tens of percent level, however little of the ice is actually lost from the grain, likely making this a robust site for in situ ice chemistry. Our models also indicate that many complex organic species should survive passage through the disk intact. This raises the possibility that organics synthesized in the interstellar medium can be delivered to terrestrial planets by icy body impact and thus potentially participate in origins of life chemistry.