  Conditions in the outer protoplanetary disk during Solar System formation
were thought to be favorable for the formation of amorphous water ice (AWI),a
glassy phase of water ice. However, subsequent collisional processing could
have shock crystallized any AWI present. Here we use the iSALE shock physics
hydrocode to simulate impacts between large icy bodies at impact velocities
relevant to these collisional environments, and then feed these results into a
custom-built AWI crystallization script, to compute how much AWI
crystallizes/survives these impact events. We find that impact speeds between
icy bodies post-planet migration (i.e., between trans-Neptunian Objects or
TNOs) are too slow to crystallize any meaningful fraction of AWI. During planet
migration, however, the amount of AWI that crystallizes is highly stochastic:
relatively little AWI crystallizes at lower impact velocities (less than ~2
km/s), yet most AWI present in the bodies (if equal sized) or impactor and
impact site (if different sizes) crystallizes at higher impact velocities
(greater than ~4 km/s). Given that suspected impact speeds during planet
migration were ~2-4 km/s, this suggests that primordial AWI's ability to
survive planet migration is highly stochastic. However, if proto-EKB objects
and their fragments experienced multiple impact events, nearly all primordial
AWI could have crystallized; such a highly collisional proto-EKB during planet
migration is consistent with the lack of any unambiguous direct detection of
AWI on any icy body. Ultimately, primordial AWI's survival to the present day
depends sensitively on the proto-EKB's size-frequency distribution, which is
currently poorly understood.
