Sodium salts in E-ring ice grains from an ocean below the surface of Enceladus

Abstract

Saturn's moon Enceladus emits plumes of water vapour and ice particles from fractures near its south pole, suggesting the possibility of a subsurface ocean. These plume particles are the dominant source of Saturn's E ring. A previous in situ analysis of these particles concluded that the minor organic or siliceous components, identified in many ice grains, could be evidence for interaction between Enceladus' rocky core and liquid water. It was not clear, however, whether the liquid is still present today or whether it has frozen. Here we report the identification of a population of E-ring grains that are rich in sodium salts ( approximately 0.5-2% by mass), which can arise only if the plumes originate from liquid water. The abundance of various salt components in these particles, as well as the inferred basic pH, exhibit a compelling similarity to the predicted composition of a subsurface Enceladus ocean in contact with its rock core. The plume vapour is expected to be free of atomic sodium. Thus, the absence of sodium from optical spectra is in good agreement with our results. In the E ring the upper limit for spectroscopy is insufficiently sensitive to detect the concentrations we found.

Dusty Plasma Effects in Near Earth Space and Interplanetary Medium

“…The results can be briefly summarized as follows: (1) the scattering of primary electrons inside the grain is critical to understanding the secondary electron emission, (2) the grain charge is determined not only by the SEE yield, but equally important is the energy distribution of secondary electrons, (3) the increase of the surface potential with decreasing grain size is predominantly caused by the increasing number of backscattered primary electrons, not by true secondary electrons. The model was successfully verified by laboratory experiments on Motivated by the Cassini observation of ice dust grains with a salt admixture in the Saturnian E-ring (Postberg et al 2009), used the last modification of the secondary emission model ) to study the secondary emission yield and surface potential of icy dust grains as a function of the grain size and the salt admixture (see Fig. 11).…”

Europa, Enceladus, and Titan as possible sites for life

“…More favorable assumptions on the availability of oxygen and/or hydrogen through the ice shell and in the ocean itself led Chyba & Hand (2001b) to estimate a steady-state biomass of ∼10 13 -10 15 g, compared with the terrestrial biomass of ∼10 18 g. On Enceladus, the discovery of the quasi-continuous ejection of plumes from the south polar region led to a "cold geyser" scenario whereby liquid water stored in high pressure pockets below the surface is vented into space in the form of vapor and fine ice particles (Porco et al 2006, Matson et al 2007, Waite et al 2009). The presence of an alkalin ocean, with a composition dominated by NaCl, NaHCO 3 , Na 2 CO 3 , and K + , is strongly suggested by the analysis of the ejected icy particles (Postberg et al 2009). Thus, the internal environment is thought to be favorable for aqueous catalytic chemistry, permitting the synthesis of many complex organic compounds.…”

Possibility for albedo estimation of exomoons: Why should we care about M dwarfs?

“…In the Solar System such subsurface oceans exist in Europa, Titan, Enceladus, and possibly also in Ganymede and Callisto. The liquid phase state of these oceans are maintained by tidal heat production, freezing point depressing solved ingredients, and/or internal heat due to accretional energy conservation and radiogenic heat (Carr et al 1998;Khurana et al 1998;Kargel et al 2000;Zimmer et al 2000;McCord et al 2001;Schenk 2002;Collins & Goodman 2007;Roberts & Nimmo 2008;Lorenz et al 2008;Postberg et al 2009;Iess et al 2014;Dobos & Turner 2015). Having information on the existence of surface ice, using mass estimation from TTV and TDV might increase the probability to identify exomoons that are probable of having subsurface oceans.…”