Slashdot Mirror
Enceladus "Sea" Mystery Deepens
Smivs writes "The BBC reports that an ocean may not be the source of the jets emanating from Saturn's moon Enceladus. Controversial research questions the moon's promise as a target in the search for life beyond Earth. A chemical analysis of Enceladus, led by University of Colorado planetary scientist Nick Schneider, failed to detect sodium, an element scientists say should be present in any body of water that has been in contact with rock for billions of years. Spectral analysis with the Keck Telescope found no sodium in the plumes or in the vapor in orbit around the moon. At stake is whether Saturn's moon could support alien life and is thus a worthy target for a NASA exploratory mission to detect it. Such a mission to Enceladus is one of four currently under review for further development."
Indeed ! Some tests are done more often then others.
Solubility of sodium chloride (or calcium chloride) in water is commonly used to prevent it from freezing (application - cleaning sidewalks).
The mixture of salt and water freezes at -21 Celsius = 272K or sooner, depending on purity. When salt water freezes it separates the salt which is why Antartic ice is not salty.
From Wikipedia, the surface temperature of Enceladus is at most 145K, so it is likely that surface ice is pure and it is possible that the liquid water is kept liquid by tidal forces (water in motion freezes at lower temperature). One can even imagine how period crystallization and melting of water by tidal forces has separated out salt somehow.
That said, sodium is extremely easy to ionize. To see that put a few salt crystals into gas or alcohol flame - it will turn yellow from the small quantity of sodium atoms that evaporated from the crystals. Thus, if liquid water was in direct contact with rock it would contain trace amounts of sodium which, when launched into space with the jet, will provide pronounced yellow line.
What is possibly happening is that two ice sheets (pure H20) collide, melt ice with the pressure and spray the resulting water into space. TFA mentions two more possibilities - as well as a speculation that Sodium atoms could be frozen inside water crystals.