Cryovolcanism
Eruption of volatile-rich icy or aqueous material — water, ammonia, methane, nitrogen — instead of silicate magma. Dominant on icy moons and small icy bodies in the outer solar system; the chief source of plume-based observability for ocean-worlds.
Observed cases
- enceladus — south-polar water-ice plumes sampled directly by Cassini.
- triton — Voyager 2 (1989) imaged dark nitrogen-driven plumes at the south polar cap.
- Ceres, Pluto, Charon — possible cryovolcanic features identified by Dawn and New Horizons.
Astrobiology relevance
Cryovolcanic plumes provide a direct sampling window into subsurface oceans without landing or drilling — the basis for the enceladus-orbilander mission concept and the broader argument in src-active-moons-review-2026-04 that plume sampling is the most accessible biosignature route on active moons.