Model of explosive eruptions of water vapor and dust on icy satellites

The possibility of generating water vapor and other gaseous products during nonvolcanic explosive eruptions in lithospheres of icy satellites is discussed. Explosive eruptions of ice, with its fragmentation into micro-and nanofragments, can occur in the extensive deep layers of such icy satellites as Europa, Ganymede, Enceladus, etc., if giant cracks are episodically formed in the lithospheres of these satellites. Such cracks can be produced by tidal forces, synchronous resonances of satellites, or especially powerful impacts. The model is based on the recently obtained experimental evidence that explosive ice instability (Bridgman effect) is formed at a strong nonuniform compression in the regions of high pressures and low temperatures. Water films, the thicknesses of which reach several microns, can be formed during the process of the mutual friction of ice fragments during their quasi-liquid flow at the instant of an explosive eruption. About 1–10 dm³ of a water film can be produced in 1 m³ of erupted ice fragments. Water vapor can be formed from a water film when this water boils up after a rapid pressure drop as a result of an ice-water mixture eruption from cracks. A certain amount of gaseous products in the form of hydrogen, oxygen, and ammonia molecules and radicals on their basis can be generated during the sputtering induced by electrons and ions and the dissociation of nanofragments of ice during the process of ice explosive fragmentation as a result of fracto-, tribo-, and secondary emission. The estimates indicate that the volume of water vapor erupted on satellites can be larger than that of discharged ionized gases by a factor of not less than 10⁵–10⁷. Water vapor and microscopic ice fragments can be erupted from cracks in the lithospheres of small Enceladus-type satellites at velocities higher than the second cosmic velocity. Gaseous products generated in such episodic processes can, most probably, substantially contribute to the density of the atmosphere that exists on small icy satellites, but can only insignificantly contribute to this density on large satellites. The stick-slip motions of the most condensed plumes of water vapor and dust, normal to the satellite surface, along the mouths of gigantic cracks may indicate that the proposed model is realistic. Such wanderings of water vapor plumes can result in the synchronous motions of thermal patches on the satellite surface along crack mouths at velocities of about 10 km/h.