cryovolcanism

Cryovolcanism is a form of volcanism on icy bodies in the outer Solar System in which volatile substances, such as water, ammonia, or methane, erupt instead of molten rock. The eruptive material is typically a mixture of water or ammonia-water and volatile ices that originates from subsurface reservoirs. Eruptions can manifest as plumes, jets, or lava-like flows on the surface that deposit fresh ice.

Observations of cryovolcanism include active plumes on Saturn’s moon Enceladus, where Cassini detected material venting from fissures in the south polar region and supplying particles to Saturn’s E ring. On Neptune’s moon Triton, Voyager 2 and subsequent studies revealed geologic features and suspected geyser-like activity consistent with cryovolcanism. The dwarf planet Ceres hosts Ahuna Mons, a prominent mountain thought to be formed by briny water-ice volcanism and related flows.

Mechanisms and conditions: cryovolcanism requires internal heat, often from radiogenic or tidal sources, to maintain pockets of liquid water or other volatiles beneath the surface. Subsurface oceans or reservoirs can become pressurized and breach the outer shell, permitting eruption. The composition of eruptions depends on internal chemistry and may include water vapor, ice particles, ammonia, methane, and organics. Eruptions can be episodic or long-lived and may be driven by tidal forcing in resonant orbits.

Implications: cryovolcanism informs models of the internal structure and thermal evolution of icy worlds and, in some cases, indicates subsurface oceans and potential habitability. The ejecta can alter surface geology and contribute material to surrounding space environments, such as Saturn’s rings.