Layered bubble-rich structures on icy worlds: experiments with large volumes of low-salinity water in near-vacuum environment.

While the geysers on Enceladus are a spectacular example of explosive cryovolcanic eruptions, active cryovolcanic effusions have not been observed in the Solar System. Signs of former cryoeffusions are only indirect, including smooth terrains with morphological resemblance to volcanic flows on Earth (Fagents, 2003; Lesage et al., 2020), thermal anomalies (Abramov and Spencer, 2009), or excess atmospheric volatiles (Quick et al., 2017). As a result, our ability to investigate the processes involved in their emplacement remains limited.

Several theoretical models have been proposed to explain and describe the origin and behavior of effusive cryovolcanism, that is, the ascent and release of subsurface water onto the surface (Allison and Clifford, 1987; Quick et al., 2017; Lesage et al., 2020). In general, water exposed to the cold, near-vacuum surface environments of icy bodies is expected to freeze with a porous skin (Bargery et al., 2010). A vast uncertainty remains, however, regarding how long it takes, how much material is lost due to vaporization and sublimation, and how porous the resulting ice is (Morrison et al., 2023; Brož et al., 2025).

In the presented work (Patočka et al., 2026), we expose 40 kg of low-salinity water in a specialist chamber at The Open University, UK, and show that freezing under near-vacuum conditions is a complex, dynamic process during which vapor puffs through the growing ice sheets, building previously unobserved ice structures. Millimeter-thin, sheet-like ice layers form, separated by centimeter-thick, large-aspect-ratio pockets of vapor. The overall height of this layered, bubble-rich ice is controlled by a balance between its weight and the equilibrium vapor pressure. In the laboratory, the height reaches approximately ten centimeters, which could plausibly extend to tens of meters in the low-gravity environments of icy bodies. The high porosity of such ice has significant implications for the interpretation of remote sensing observations, and its fragile character makes terrains created by effusive cryovolcanism hazardous for spacecraft landing. 

This work was funded by the Czech Grant Agency grant No. 25- 15473S. VP has been supported by the Charles University Research Centre program No.~UNCE/24/SCI/005. MRP acknowledges support from the UK Space Agency/STFC through grants UKRI2545, ST/X006549/1, ST/Y005929/1, ST/Y000234/1 and ST/X001180/1.

References:

Abramov, O., Spencer, J.R., 2009, doi:10.1016/j.icarus.2008.07.016.
Allison, M., Clifford, S., 1987, doi.org/10.1029/JB092iB08p07865
Bargery, A.S., Lane, S.J., Barrett, A., Wilson, L., Gilbert, J.S., 2010, doi:10.1016/j.icarus.2010.06.019.
Brož, P., Patočka, V., Butcher, F., Sylvest, M., Patel, M., 2025, doi:10.1016/j.epsl.2025.119531.
Fagents, S.A., 2003, doi:10.1029/2003JE002128.
Lesage, E., Massol, H., Schmidt, F., 2020, doi:10.1016/j.icarus.2019.07.003.
Morrison, A.A., Whittington, A.G., Mitchell, K.L., 2023, doi:10.1029/2022JE007383.
Patočka, V., Brož, P., Chan, K., Sindhu, P., Fox-Powell, M., Sylvest, M., Emerland, Z., Patel, M., 2026, submitted