[X] My Assistant

[vexgizmo]

OK, it's time to have it out. Is Enceladus really spewing water, or are its fractures effectively sublimating warm ice like a comet?

Have a careful read of the Enceladus Science papers (specifically Porco et al vs. Spencer et al.) and you will see that the evidence for water is equivocal, and arguably circular. The prime piece of evidence for liquid water (Porco et al) is the inferred high ice/vapor ratio of the plume (top of p. 1398). This is inferred from scattering models and assumptions of plume particle sizes and argued unlikelihood of particle entrainment in sublimating gas (explained briefly in their note 30, and into p. 1399). Should we hang our conclusions, exploration strategies, and hopes for life on moels of ice/vapor ratio, particle size assumptions, and inferred difficulty of entraining particles in sublimated gas?

Instead (Spencer et al), the fractures of Enceladus may simply expose warm (T ~ 180K) ice which sublimates like a comet (p. 1405).

Show me the water.

[Guest_BruceMoomaw_*]

Raul Baragiola confirms that Frank Crary and I misunderstood his theory at the Europa Focus Group meeting. His theory is that Enceladus may actually have ammonia -- but NOT, as we thought, that a substantial amount of it is releaesd in the vapor plume but is then broken down virtually completely into nitrogen by Saturn's charged-particle radiation before it can reach Cassini's mass spectrometer. he agrees that that is impossible during the brief 15 minutes of transit from surface to Cassini.

Instead, he agrees with Bob that Enceladus may not have liquid geysers at all, and that its vapor plume is instead released from the surface of warm, sublmating ice. But while Dennis Matson and comapny think that Enceladus' internal ammonia is broken down into N2 and H2 by the hot geothermal processes occurring in the moon's rocky core before it ever gets into the ice mantle, baragiola thinks it may actualy be incorporated into the ice as ammonia, and get slowly carried to Enceladus' surface by solid-state ice convection -- but that, within just a few days of its reaching the surface, Saturn's radiation breaks it down completely into N2 and H2. And he thinks that this happens at a rate much faster than the rate at which the water vapor sublimates off the surface of the warm ice -- so that, by the time the vapor lifts off from Enceladus' surface, it already contains only a small trace of ammonia, with most of it having already been turned into nitrogen and hydrogen that was temporarily trapped in the ice after its creation.

He also thinks there's a real chance that there is no subsurface liquid-water sea inside Enceladus at all, and that we may just be seeing continuous slow solid-state convection of solid ice contacting the warm top surface of the rocky core. This, however, is not necessary to the rest of his theory -- as I said earlier, there could be a subsurface water sea with ammonia mixed into it, freezing at its top with the ice gradually convecting to the surface from there.