Plume experiments to constrain Enceladus ocean composition and subsurface conditions

Icy moons exhibiting cryovolcanism provide rare opportunities to probe material originating from their interiors and assess the potential for habitable environments. Observations of the water vapour and ice plume at Enceladus’ south pole by the Cassini spacecraft revealed a salty subsurface ocean with a basic pH and traces of organic compounds. The leading plume formation mechanism involves the vaporisation of liquid water beneath the ice shell, followed by rapid ascent through near-vertical crevasses. However, significant uncertainties remain in linking plume composition to that of the subsurface ocean, and in identifying the processes that control plume formation and influence material transport. We conducted laboratory experiments designed to study Enceladus-like plumes and assess how the ocean composition and ice-shell conditions affect eruption dynamics. Our setup consists of a water reservoir and a narrow channel representing the subsurface ocean and ice fractures, placed inside a vacuum chamber to simulate the low-pressure environment. Our results show that lower crevasse temperatures lead to higher venting speeds and ice-to-vapour fractions. Moreover, gas exsolution from the liquid phase can accelerate the flow and loft droplets that act as nuclei for ice grain formation. These findings indicate that the velocity of a single eruption and its ice grain abundance are strongly controlled by thermal conditions and dissolved gas content, rather than solely by crevasse geometry.