Cryovolcano
[4]: 768 Effusive cryovolcanism takes place with little to no explosive activity and is instead characterized by widespread cryolava flows which cover the pre-existing landscape.
Fractures in particular, either the result of global or localized stress in the icy crust, providing potential eruptive conduits for cryomagma to exploit.
True polar wander, where the object's surface shifts relative to its rotational axis, can introduce deformities in the ice shell.
[12]: 675 Evidence for subsurface oceans also exist for the dwarf planets Pluto[13] and, to a lesser extent, Ceres,[14][15] Eris, Makemake,[16]: 8 Sedna, Gonggong, and Quaoar.
A convective layer in the ice shell can generate warm plumes that spread laterally at the base of the brittle icy crust.
[3]: 174 Intrusive models, meanwhile, propose that a deeper subsurface ocean directly injects cryomagma through fractures in the ice shell, much like volcanic dike and sill systems.
A partially frozen ammonia-water eutectic mixture can be positively buoyant with respect to the icy crust, enabling its eruption.
Upon the arrival of the Dawn orbiter in March 2015,[21] the dwarf planet was discovered to have numerous bright spots (designated as faculae) located within several major impact basins, most prominently in the center of Occator Crater.
These bright spots are composed primarily of various salts, and are hypothesized to have formed from impact-induced upwelling of subsurface material that erupt brine to Ceres's surface.
The distribution of hydrated sodium chloride on one particular bright spot, Cerealia Facula, indicates that the upwelling occurred recently or is currently ongoing.
[24]: 452 [25] Its most striking features, a dense web of linear cracks and faults termed lineae, appear to be the sites of active resurfacing on Europa, proceeding in a manner similar to Earth's mid-ocean ridges.
[3]: 193–194 Nevertheless, observations of Europa from the Hubble Space Telescope (HST) in December 2012 detected columns of excess water vapor up to 200 kilometres (120 miles) high, hinting at the existence of weak, possibly cryovolcanic plumes.
In 2011, Europa's chaos terrain, where the crust appears especially disrupted, was interpreted by a team of researchers as the site of very shallow cryomagma lakes.
[18] Later, in 2023, a field of cryovolcanic cones was tentatively identified near the western edge of Argadnel Regio, a region in Europa's southern hemisphere.
[37]: 42 Saturn's moon Titan has a dense atmospheric haze layer which permanently obscures visible observations of its surface features, making the definitive identification of cryovolcanic structures especially difficult.
From Cassini radar data, several features have been proposed as candidate cryovolcanoes, most notably Doom Mons, a mountain reminiscent of a shield or dome edifice; and the neighoring Sotra Patera, an ovular depression that resembles a caldera.
Wood and Jani Radebaugh that they form from either maar-like eruptions—forming by explosions of boiling subsurface liquid as it is rapidly heated by magma (in this case, cryomagma)[41]: 6 —or the flooding of collapse calderas.
[42] Of Uranus's five major satellites, Miranda and Ariel appear to have unusually youthful surfaces indicative of relatively recent activity.
These characteristics have led to several teams of researchers to propose a cryovolcanic origin of the coronae, where eruptions of viscous cryomagma form the structures with some tectonic involvement.
In 2014, a team of planetary scientists interpreted these depressions as diapirs, caldera collapse structures, or impact craters filled in by cryolava flows.
[6]: 922 Triton's southern polar ice cap is marked by a multitude of dark streaks, likely composed of organic tholins deposited by wind-blown plumes.
[52]: 3–4 The dwarf planet Pluto and its system of five moons were explored by the New Horizons spacecraft in a flyby on 14 July 2015, observing their surface features in detail for the first time.
[54][55] The two mountains are surrounded by an unusual region of hilly "hummocky terrain", and the lack of distinct flow features have led to an alternative proposal in 2022 by a team of researchers that the structures may instead be formed by sequential dome-forming eruptions, with nearby Coleman Mons being a smaller independent dome.
[58]: 7 Similarly, in 2021 a team of planetary scientists led by A. Emran proposed that Kiladze, a feature that is formally classified as an impact crater, is actually a cryovolcanic caldera complex.
[61] In 2022, low-resolution near-infrared (0.7–5 μm) spectroscopic observations by the James Webb Space Telescope (JWST) detected light hydrocarbons and complex organic molecules on the surfaces of the dwarf planets Quaoar, Gonggong, and Sedna.
[17]: 13 JWST spectral observations of Eris and Makemake revealed that hydrogen-deuterium and carbon isotopic ratios indicated that both dwarf planets are actively replenishing surface methane as well, possibly with the presence of a subsurface ocean.
[16]: 8 These observations, combined with the discoveries in the Pluto system by the New Horizons spacecraft, indicate that icy worlds are capable of sustaining enough heat on their own to drive cryovolcanic activity.
