Dynamics of gas-driven eruption on Ceres as a probe to its interior

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2023-08, Vol.400, p.115533, Article 115533
• Main Authors: Yumoto, Koki, Cho, Yuichiro, Koyaguchi, Takehiro, Sugita, Seiji
• Format: Article
• Language: English
• Subjects: Asteroid Ceres; Asteroids, surfaces; Volcanism
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2023.115533

The mineralogy of localized bright deposits on Ceres observed by the DAWN mission suggests their brine-enriched cryovolcanic origin. Based on the morphological observations of these deposits, explosive and effusive styles have been proposed for their eruption. Because volcanic eruption style and velocity are controlled by the extent of gas expansion inside the conduit, constraints on the internal aqueous environment, such as gas concentration and temperature, could be placed based on the observations of localized deposits on Ceres. However, the way these properties control the eruption style and velocity is complex. Cryomagma ascending from a subsurface reservoir gains buoyancy due to both boiling of water and exsolution of dissolved gas, owing to decompression to the extremely low pressure near the Ceres surface. Gas–melt segregation should also affect the dynamics. Thus, it is not yet fully understood how the internal environment of Ceres affects the ascent dynamics of cryovolcanism and subsequently controls the styles (explosive versus effusive) and velocities of eruptions. To address this problem, we developed a one-dimensional steady-state two-phase flow model for the ascent dynamics of gas-driven cryomagma under the conditions of Ceres taking both water boiling and gas exsolution into account. We found that the velocity and explosivity of an eruption are strongly controlled by the following three parameters, which characterize the cryomagmatic environment of Ceres's interior: (a) conduit conductivity (CC; rc2/μ, where rc is the conduit radius and μ is the magma viscosity), (b) dissolved gas concentration c0, and (c) magma reservoir temperature T0. Our model results reveal that low CC always leads to effusive or low-explosivity eruptions. Higher CC allows explosive eruption when either c0 or T0 is sufficiently high. These dependences can be summarized as four modes of eruption under the following CC-c0-T0 conditions. (1) Exsolution-driven explosive eruptions (X1 type) occur with volatile-rich magma (CC ≳ 10−3 m2/(Pa·s) and c0 ≳ 0.1 wt% of CO2). (2) Boiling-driven explosive eruptions (X2 type) occur with warm magma (CC ≳ 10−3 m2/(Pa·s), c0 ≪ 0.1 wt% of CO2, and high T0). (3) Viscosity-induced effusive eruptions (F1 type) occur with a narrow conduit and/or high-viscosity magma (CC ≲ 10−3 m2/(Pa·s)). (4) Low-gas-production-induced effusive eruptions (F2 type) occur with low-temperature and low-volatile magma (CC ≳ 10−3 m2/(Pa·s), c0 ≪ 0.1 wt% of CO2, and