| Abstrakt: |
There is considerable interest in sending a mission to Enceladus to sample its erupting materials, which are sourced from its ocean, a proposed habitable environment. However, we lack resolution between competing ascent and eruption models, which offer differing consequences and challenges for mission sampling and access strategies. We report a new Enceladus ascent and eruption model, "Cryo‐Erupt," where ascent from ocean to jet is driven by the exsolution and expansion of dissolved gases from ascending water within conduits. This mechanism shares many similarities with some forms of terrestrial activity, including explosive silicate volcanism, cold‐water geysers and "limnic" eruptions. This preliminary study suggests that this mode of ascent and eruption is viable and broadly consistent with a range of observations including the apparent co‐existence of point‐ (jet) and fissure‐ (curtain) sourced activity as well as strong contrasts in velocity and ice‐to‐vapor ratio between the plume and the jets feeding it. However, it requires the co‐existence of a sublimation plume as an additive component to the broader plume. The outcomes of the Cryo‐Erupt model differ in terms of conduit physical and chemical processes from previously proposed boiling interface eruption models, for example, predicting larger dynamic pressures and narrower conduits, which could present challenges for direct robotic access. Due to the lack of a static boiling interface or wall condensation, bulk composition is unlikely to change appreciably during ascent from the ocean‐conduit interface to the jet, potentially simplifying the interpretation of samples collected in space or on Enceladus' surface. Plain Language Summary: High‐speed jets from giant ice fissures on Saturn's moon Enceladus feed a large plume, which is of interest to scientists because it contains salts and organic compounds, which are evidence of a subsurface ocean that may possibly host life. However, it is unclear how the chemistry of the plume material (gas and grains) might be altered as this material moves from the ocean into space, and to what extent samples from the plume are representative of ocean composition. Previous models to predict this behavior mostly relied on boiling of water as the primary way that gas and droplets are ejected, but these models do not take into account all of the physics involved, and do not fully reproduce what Cassini observed at Enceladus. We propose a new model that instead invokes dissolved gas molecules expanding, similar to explosive volcanoes on Earth and essentially the same mechanism that causes cans of soda to explode upon opening if shaken. We predict that the erupting jets would largely preserve bulk ocean content and thus would be the best place to study ocean content, in contrast with the broader plume, which would have more water that has sublimated from the surface. Key Points: Recent studies on the ascent and eruption of Enceladus' plume have neglected the role of exsolution and expansion of dissolved volatilesVolatile‐driven direct ocean‐to‐jet liquid water ascent is generally consistent with observations if combined with a sublimation co‐plumeThis mode of ascent could preserve ocean bulk content in jets, leading to jet sampling strategies being preferred for future missions [ABSTRACT FROM AUTHOR] |
Plný text