Prerequisites for explosive cryovolcanism on dwarf planet-class Kuiper belt objects

Abstract

Explosive extrusion of cold material from the interior of icy bodies, or cryovolcanism, has been observed on Enceladus and, perhaps, Europa, Triton, and Ceres. It may explain the observed evidence for a young surface on Charon (Pluto's surface is masked by frosts). Here, we evaluate prerequisites for cryovolcanism on dwarf planet-class Kuiper belt objects (KBOs). We first review the likely spatial and temporal extent of subsurface liquid, proposed mechanisms to overcome the negative buoyancy of liquid water in ice, and the volatile inventory of KBOs. We then present a new geochemical equilibrium model for volatile exsolution and its ability to drive upward crack propagation. This novel approach bridges geophysics and geochemistry, and extends geochemical modeling to the seldom-explored realm of liquid water at subzero temperatures. We show that carbon monoxide (CO) is a key volatile for gas-driven fluid ascent; whereas CO 2 and sulfur gases only play a minor role. N 2 , CH 4 , and H 2 exsolution may also drive explosive cryovolcanism if hydrothermal activity produces these species in large amounts (a few percent with respect to water). Another important control on crack propagation is the internal structure: a hydrated core makes explosive cryovolcanism easier, but an undifferentiated crust does not. We briefly discuss other controls on ascent such as fluid freezing on crack walls, and outline theoretical advances necessary to better understand cryovolcanic processes. Finally, we make testable predictions for the 2015 New Horizons flyby of the Pluto-Charon system.

Core cracking and hydrothermal circulation can profoundly affect Ceres' geophysical evolution

“…Whether these sources arise from sublimation of near-surface ice or from cryovolcanism is unknown. Cryovolcanism may be favored by freezing, which could pressurize liquid water reservoirs [Fisher, 2003;Neveu et al, 2015]. Our results suggest that under certain conditions (late accretion, presence of antifreezes) it might be possible for Ceres to undergo global freezing at the present day (Figures 7b and 7c).…”

“…On the other hand, Ceres formed further away from the Sun than the Earth and could have accreted a higher proportion of volatiles [ Desch et al , ; Castillo‐Rogez and McCord , ; Sohl et al , ], some of which have a lower vapor pressure than water. Thus, careful treatment of gas processes should include not only water vapor but also primordial volatiles and those formed as a consequence of endogenic activity, such as ammonia, methane, molecular hydrogen, or carbon dioxide [ Neveu et al , ]. We leave the inclusion of these species for future work.…”

Compaction and Melt Transport in Ammonia‐Rich Ice Shells: Implications for the Evolution of Triton

“…; Kalousová et al, 2016;Neveu et al, 2015;Quick & Marsh, 2016;Showman et al, 2004). Future models could examine more complex chemical systems, melt transport through fractures, and Rayleigh-Taylor instabilities, as well as the influence of topographically induced pressure gradients (cf.…”

“…Future models could examine more complex chemical systems, melt transport through fractures, and Rayleigh-Taylor instabilities, as well as the influence of topographically induced pressure gradients (cf. ; Kalousová et al, 2016;Neveu et al, 2015;Quick & Marsh, 2016;Showman et al, 2004). Incorporating eutectic melting into advanced two and three dimensional models could significantly advance our understanding of melt migration on icy satellites.…”

Cryomagma ascent on Europa

“…Manga and Wang (2007) showed that liquid water is unlikely to rise directly from the internal ocean to the surface through large fractures because of the extremely high pressure required for this mechanism to work. For example, even for an extreme thickness of 50 km of ice, freezing of a few kilometers of water in the ocean would induce a 1-10 kPa overpressure, which is enough to propagate a fracture over the ice crust thickness (Manga and Wang, 2007;Neveu et al, 2015) but not to bring water from the ocean to the surface: a few MPa are necessary to drive the water past the level of neutral buoyancy. On the other hand, recent literature demonstrated the possibility of the emplacement of common geological features at Europa's surface, such as double ridges (Dombard et al, 2013;Johnston and Montési, 2014;Dameron and Burr, 2018), chaos (Greenberg et al, 1999;Schmidt et al, 2011) and lenticulae (Manga and Michaut, 2017) by the presence of near-surface liquid water reservoirs.…”