Possible evidence for a methane source in Enceladus' ocean

Abstract

International audienceThe internal ocean of Enceladus can be expected to present conditions favorable to the trapping of volatiles in clathrates. This process could influence the eventual composition of the ocean and therefore of the plumes emitted by the south polar region. Here we used a statistical thermodynamic model to assess which species detected in the plumes by the Cassini-Ion and Neutral Mass Spectrometer experiment are trapped in clathrates. We treated Enceladus' internal ocean as a terrestrial subglacial lake with a mixture of dissolved volatiles indicated by plume gas measurements. We find that the conditions for clathrate formation are met in this ocean, except above 20km or in hypothetical hot spots. The formation of multiple guest clathrates depletes methane below plume levels, suggesting that clathrates eventually dissociate (releasing methane) in the fissure that connects the ocean to the surface or that another mechanism (such as hydrothermal reactions) is compensating by adding methane into the ocean

Earth as a Tool for Astrobiology—A European Perspective

“…Similar environments might exist on Europa or Enceladus, which have icy crusts and possibly liquid oceans beneath. In fact, magnesium sulphate salts have been detected in Europa's ice surface using the Keck II telescope, possibly providing a sample of the ocean underneath (Brown and Hand 2013) and in the plumes of Enceladus (Bouquet et al 2015). Early Archaean Terrains The early Earth represents an ideal environmental and microbial analogue for early habitable bodies in the Solar System.…”

Properties of CO2clathrate hydrates formed in the presence of MgSO4solutions with implications for icy moons

“…Among the gases such as CH 4 present in the plumes emanating from the satellite's surface (Waite et al 2006), CO 2 has poor solubility in water. This suggests the trapping of gases in the form of clathrate hydrates, with subsequent release due to their dissociation (Bouquet et al 2015) could give rise to the plumes. Fortes (2007) used a clathrate xenolith model to account for the origin of Enceladus' plumes, suggesting that fluids are able to break through the ice shell, metasomatising the mantle by the emplacement of clathrates along fractures and grain boundaries.…”

“…On the other hand if they ascend, then a clathrate layer would be present at the interface between the ice and ocean surface. Bouquet et al (2015) calculated the density of clathrates assuming fully filled cages and a volatile composition based on Enceladus' plume; they found densities of 1.04 g cm −3 and 0.97 g cm −3 for sI and sII clathrates respectively. When comparing these to their computed ocean densities they deduced that sII clathrates should be buoyant and therefore likely to ascend.…”

“…However they were unable to arrive at a conclusion regarding the sI clathrates, as there was significant uncertainty regarding the ocean's salinity, and because the clathrate density was too close to that of the ocean itself. Clathrate ascension would, however, enable clathrates to play a part in the formation of the plumes, as their dissociation would increase pressure conditions at the site of the plume's origin (Bouquet et al 2015).…”

Detection of Biomarkers in Gas Plumes Using a Multi-Spectral Camera in the Proposed Enceladus Orbiter Mission (NASA)

“…Dyskusja dotycząca istnienia i warunków panujących w ewentualnym oceanie pod lodową warstwą zewnętrzną na Enceladusie [2,11,13,24,25], zwróciła uwagę na wydobywające się przez obecne na południowej półkuli księżyca szczeliny pióropusze gazów (rys. 1) i wypracowanie metodyki pośrednich pomiarów składu chemicznego oceanu, jego pH i temperatury, dostępnej do wykorzystania energii oraz zachodzących w jego wnętrzu procesów geologicznych za pomocą oceny parametrów pióropuszy [4].…”