The Effects of Early Collisional Evolution on Amorphous Water Ice Bodies

Abstract

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 we 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 after planet migration (i.e., between trans-Neptunian objects) 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−1), yet most AWI present in the bodies (if equally sized) or impactor and impact site (if different sizes) crystallizes at higher impact velocities (greater than ∼4 km s−1). Given that suspected impact speeds during planet migration were ∼2–4 km s−1, this suggests that primordial AWI’s ability to survive planet migration is highly stochastic. However, if proto-Edgeworth–Kuiper Belt (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.

Quantifying Morphological Changes and Sediment Transport Pathways on Comet 67P/Churyumov‐Gerasimenko

“…These remnants of the earliest era of planetary formation were eventually transported to their current reservoirs through planetary migration and/or interactions with other stars and gas clouds (A’Hearn et al., 2012). While these objects have undergone significant processing before entering their current reservoirs (Lisse et al., 2022; Steckloff et al., 2023), they represent some of the least processed materials in the solar system. Jupiter Family Comets (JFCs) are of particular interest for scientific study due to their short orbital periods, and close perihelion passages that permit detailed spacecraft observations.…”