[X] My Assistant

[jsheff]

Enceladus just jumped to way near the top of the list of biologically interesting places. We know how to get to Mars; we some ideas of further exploration of Euiropa and Titan. Has anyone designed a mission to land on Enceladus? What would it take? How much delta vee?

[centsworth_II]

Wouldn't the water pocket sit directly on the hot rock? How could there be ice between the water and hot rock?

[The Messenger]

Wouldn't the water pocket sit directly on the hot rock? How could there be ice between the water and hot rock?

Focused Lasers, if they have the technology, focused sound waves or radar, if they don't

[centsworth_II]

Focused Lasers, if they have the technology, focused sound waves or radar, if they don't

Hey, I've read about natural nuclear reactors existing in Africa millions of years ago, so who knows?

Pressure. Lots of it.

So the ice between the water pocket and rock is actually warmer than the water, but pressure is keeping it solid? That makes sense to me. Of course no one knows the real situation, but if that's a possibility...

[The Messenger]

Hey, I've read about natural nuclear reactors existing in Africa millions of years ago, so who knows?
So the ice between the water pocket and rock is actually warmer than the water, but pressure is keeping it solid? That makes sense to me. Of course no one knows the real situation, but if that's a possibility...

No, because pressure causes freezing point elevation, not depression. It is difficult to see how a geyser could form from direct sublimation of water-ice. It takes to many calories to transition both phases, and still have enough gas pressure to direct the molecules upward.

I think a better answer is that there are pockets of water under the ice, or in a rock matrix. This water would immediately erupted into the gaseous phase if and when exposed to Enceladus surface pressure, and as these jets emerge, it also seems likely that the amount of heat energy removed would quickly freeze the water in a very dynamic, cyclic process of eruptions...unless the heat source is extremely hot.

This one is going to take some time, and more data, to sort out.

[Guest_Richard Trigaux_*]

No, because pressure causes freezing point elevation, not depression.

False: until about 1600 bars, the freezing point of pure water decreases about 1°C for every 100 bars. Only after high pressure ice have a freezing point raising with pressure, as for most bodies. But I think such pressure cannot be reached on Enceladus.

[The Messenger]

False: until about 1600 bars, the freezing point of pure water decreases about 1°C for every 100 bars. Only after high pressure ice have a freezing point raising with pressure, as for most bodies. But I think such pressure cannot be reached on Enceladus.

So for water ice under the conditions expected at Enceladus, what is the heat of sublimation?

[Guest_Richard Trigaux_*]

So for water ice under the conditions expected at Enceladus, what is the heat of sublimation?

Sorry, I don't know this. Google it: water ice enthalpy.

At rough guess, only relatively hot ice can sublimate. -50°C, -100°C? It is still hotter than what was measured. But the measures were doing an averaging on distance of several kilometres. So there may be much hotter point, up to zero.

Anyway to maintain the sublimation rate observed, we need a constant renewing of ice. Or the ice has a karst form, with cavities where the sublimation takes place. That is: sublimation would quickly stop on parts of ice directly exposed to space. But it would continue in underground cavities, which will become larger and larger. So a realy difficult place for a lander, with hidden holes, tracherous ground, sharp spikes, etc. But once into such a cavity, it is really the best place to search for microbes, or whatever there is.


Some here prefer to speak of water flowing rather than ice sublimating. This would better expect the quick variations of the plumes. But sublimation could give variations too, for instance when a cavity roof is crumbling down.


You need the heat of sublimation, but for any calculus we first need the mass of gasses produced.

[Bob Shaw]

Surely there are well-observed examples of water-ice sublimation from subsurface reservoirs producing plumes?

I think they're called 'comets'.

Bob Shaw

[Guest_Richard Trigaux_*]

Surely there are well-observed examples of water-ice sublimation from subsurface reservoirs producing plumes?

I think they're called 'comets'.

Bob Shaw

Indeed I don't see any difference between comet plumes and Enceladus plumes.

Anyway in vacuum any plume takes the same shape.

The Cassini scientists insist as what the plumes would be sharp because they would be forced out of vents. But in vacuum, whatever it is a rocket exhaust or snow sublimating, the plume is alway about the same shape.

[climber]

Indeed I don't see any difference between comet plumes and Enceladus plumes.

Anyway in vacuum any plume takes the same shape.

The Cassini scientists insist as what the plumes would be sharp because they would be forced out of vents. But in vacuum, whatever it is a rocket exhaust or snow sublimating, the plume is alway about the same shape.

Is that also true on Triton ? Io ?

[Bob Shaw]

Is that also true on Triton ? Io ?

No. Triton's plumes went straight up in the thin atmosphere, and then sheared in high altitude winds. Some of Io's plumes might be hot enough to glow in visible light, so they could look rather different to the rocket exhaust style of outflow. And after that, they're made of quasi-volcanic materials rather than ices, so may well follow more discrete parabolic paths with less diffusion.

Bob Shaw