Experimental Investigations on the Effects of Dissolved Gases on the Freezing Dynamics of Ocean Worlds

Abstract

The surfaces of icy moons are covered by fractures, other tectonic features, and active or ancient remains of cryovolcanism. These observations suggest active or recent tectonics, but there is still much unknown about the specific conditions surrounding the formation of these features. One important process leading to the fracture of the ice shell is the freezing and consequent pressurization of its ocean, because water expands upon freezing. However, the influence of dissolved non‐condensable gases (herein referred to as volatiles) on the aforementioned dynamics remains poorly constrained. In this study, we present a new experimental investigation to explore the effect of dissolved volatiles in the internal pressure evolution of 10 cm diameter water spheres subjected to freezing temperatures between ~−60°C and ~−20°C. Our experiments reveal that spheres with a reduced initial amount of volatiles dissolved undergo an abrupt transition with dramatic increase of (a) the time between consecutive ice shell fractures and (b) the pressure required to break the shell. We show from a simple numerical model that this transition occurs when exsolution (i.e., nucleation and growth of bubbles) occurs and the fluid inside the shell becomes significantly more compressible. Exsolution is, in turn, triggered by the gradual thickening of the ice shell, which increases the concentration of dissolved volatiles and eventually leads to saturation. These results suggest that the content of volatiles of icy satellites plays a significant role in their geologic history and potential for habitability.

Cratering and Tectonic History of the Largest Uranian Satellite, Titania: New Insights Enabled by Image Reprocessing

“…These newly identified fractures (e.g., Figure 5(A)) include some that split into multiple parallel branches, similar to those observed to cross Ursula crater. The broad extent of the fracture network supports the idea that these fractures, including larger features like Messina Chasmata, formed in response to global stresses, perhaps caused by the freezing of a subsurface ocean (Smith et al 1986;Manga & Wang 2007;Berton et al 2020) and/or tidal stresses (Schenk & Moore 2020). Croft & Soderblom (1991) mapped lineaments extending from Gertrude near the terminator.…”

Geometry of Freezing Impacts Ice Composition: Implications for Icy Satellites

“…This combination of tensional, compressional, and rotational stresses has been suggested as a process capable of generating several of the fractural and other geological features seen across the surfaces of icy moons in the solar system (e.g., the tiger stripe fractures of Enceladus (Nimmo, 2020; Rudolph & Manga, 2009), ridges (Dombard et al., 2013; Head et al., 1997; Hoppa et al., 1999; Manga & Sinton, 2004), dilational bands (Howell & Pappalardo, 2018; Prockter et al., 2002), fractures (Dombard et al., 2013; Helfenstein & Parmentier, 1983; Nathan et al., 2019; Rudolph & Manga, 2009; Walker et al., 2014, 2021), strike slip faults (Hoppa et al., 1999, 2000; Kalousová et al., 2016; Nimmo & Gaidos, 2002), and sill/lens/dike evolution on Europa (Chivers et al., 2021; Craft et al., 2016; Manga & Michaut, 2017; Michaut & Manga, 2014), and global scale fractures across less geologically modified icy worlds (Ganymede, Charon, Iapetus) (Nathan et al., 2019)). Additionally, the solidification of the underlying ocean during initial ice shell formation or periodic/regional thickening will generate significant internal pressure, due to the density difference between ice and water, that could lead to fracture generation (Berton et al., 2020; Manga & Wang, 2007). If these fractures are connected to a fluid reservoir (either the underlying ocean or a perched water body within the shell) they are prone to infiltration by the fluid, upon which heat loss to the cold fracture walls should induce freezing of the injected brine.…”

Geometry of Freezing Impacts Ice Composition: Implications for Icy Satellites

“…Additionally, the solidification of the underlying ocean during initial ice shell formation or periodic/regional thickening will generate significant internal pressure, due to the density difference between ice and water, that could lead to fracture generation [Berton et al, 2020;Manga and Wang, 2007]. If these fractures are connected to a fluid reservoir (either the underlying ocean or a perched water body within the shell) they are prone to infiltration by the fluid, upon which heat loss to the cold fracture walls should induce freezing of the injected brine.…”