CLAM: a Crevasse Laboratory Analogue for icy Moons to recreate and study plumes

Once a mighty giant follower of Kronos in the Gigantomachy, crushed beneath Mount Etna by Athena, Enceladus now slumbers in the icy grip of Saturn’s embrace. Its cryovolcanic plumes, rich in water vapour and organic molecules, rise like spectral echoes of its mythical past, making this enigmatic moon a beacon in the search for life beyond Earth. Both the European Space Agency (ESA) and NASA are planning missions to return to the Cronian system, via a large-class mission and a flagship mission respectively, aiming to unravel the mysteries of this icy moon.

To support such efforts, experimental modeling is essential, providing critical data to guide mission planning and maximise the scientific return of future in situ observations. In this context, the Crevasse Laboratory Analogue for icy Moons (CLAM) experimental setup, presented in this work, offers valuable insight into water vapour flow conditions inside the ice shell fractures of Enceladus.

The setup uses 3D-printed straight cylindrical channels, designed using key dimensionless scaling parameters, the Reynolds, Knudsen, Prandtl, and Eckert numbers, to serve as crevasse analogues. Each channel is mounted atop a cylindrical reservoir filled with demineralised water and placed inside our environmental chamber, PISCES (Plumes and Ices Simulation Chamber for Enceladus and other moonS). The channel is instrumented with differential pressure sensors and thermocouples to monitor the evolution of vapour flow as the chamber pressure is reduced to sub-millibar levels (~5×10-2  mbar). It is also externally cooled to sub-zero temperatures (~255 K) using frozen aluminium pellets. Finally, the velocity of the emerging plume is measured using an L-shaped Prandtl (Pitot-static) tube.

Our results present how plumes develop in different channels at cold temperature (~255 K), and which velocities are reached within the channel and at the vent. We show that channel temperatures have an important effect on the velocities of plumes, and discuss these effects. Notably, supersonic gas plumes were observed in several cases, with some configurations reaching supersonic speeds within the channel while others accelerated beyond the vent.