Sunday, July 17, 2005

Enceladus thoughts and more

Just giving everyone a heads up: I will be out of town starting tonight and will be in Flagstaff for a Titan Surfaces Meeting until Tuesday evening. While I am at it, yes Dad, I got the package. Thanks for the cookies! Anyways, my connection to the internet maybe spotty so don't expect too many updates here over the next couple of days.

On to Enceladus. This little moon continues to amaze. The views of this moon's south polar region were spectacular, including one very high resolution shot taken from a distance of only a few hundred km. Immediately one thinks of Europa, but one has to be careful comparing two very differently sized worlds. I can't count out the possibility of a liquid ocean, but the small size of Enceladus and the prevalence of cratered terrain makes me think that is not what we are see here. I think a more apt analogy is Miranda, with its own dichonomy between concentric ridged corona and heavily cratered terrain. In the case of Miranda, it is thought that upwellings of warm ice produced the coronae. A similar formation mechanism could be invisioned for Enceladus.


Anonymous MiniTES said...

Jason, do you know of any internet references on Mirandan geology that are above press-release level stuff? There doesn't seem to be any real online material.

7/17/2005 04:39:00 PM  
Blogger Bruce Moomaw said...

I think there's something more dramatic going on at Enceladus than at Miranda. First, we have the multiple evidence for outgassing, which indicates current activity. Then, we have the extreme youth of some of the tectonic features -- just look, for instance at .

I think that what we're seeing at Enceladus -- just as it's believed we're seeing it at the inner three Galilean satellites -- is INTERMITTENT tidally stimulated geological activity over cycles of tens to hundreds of millions of years, produced by the fact that the moons keep drifting into and out of more or less intense resonance relationships as they slowly spiral away from their central planets. In the case of Enceladus, the cycles are a lot slower and less intense than with Europa -- a matter of 100 or 200 million years, rather than just a few tens of millions, and not intense or widespread enough to obliterate most of the moon's craters -- but they are nevertheless there. I suspect Enceladus' remaining outgassing is a result of the fact that it's still cooling off from its last period of maximum tidal heating. But I also wouldn't be surprised if, even at its maximum, Enceladus' geological activity didn't take the form of oozing warm-ice diapirs with only a relatively small amount of liquid water/ammonia mixed in, just as Jason sggests.

7/17/2005 05:11:00 PM  
Anonymous Steve Albers said...

There is a good article on Miranda a few months back in the "Planetary Report" put out by The Planetary Society. The author is Bob Pappalardo.

7/18/2005 10:05:00 AM  
Anonymous MegaTES said...

What about free resources?

I've supersized my name for today. Sounds more like a B-movie monster than a boring ol' thermal emission spectrometer on Mars.

7/18/2005 01:29:00 PM  
Blogger Mossbury said...

Apropos comparison Miranda / Enceladus. Enceladus is a much smoother body than Miranda so I guess has been subject to more melting. It is also more dense.


7/19/2005 12:05:00 AM  
Blogger Jason said...

My comment is to mainly get the point out that just because 50% of the surface has a resemblance to Europa, doesn't mean you can invoke an ocean hypothesis, when there are SO MANY differences between Europa and Enceladus. First, the other 50% looks nothing like Europa, being heavily cratered. Second, the difference in size between Enceladus and Europa is enormous. You just can geophysically make a one for one comparison. I certainly agree with Bruce, episodic tidal heating that allows for localized resurfacing before it falls out of resonance is certainly reasonable, IMHO, but I don't know of any models have been done to examine its feasibility.

So my comparison to Miranda had more to do with that it a more reasonable analog for Enceladus than Europa, but as he points out, even that has problems.

7/20/2005 10:26:00 AM  
Blogger Mossbury said...

I read some time ago, that based on the shape of Enceladus, and assuming hydrostatic equilibrium, the density would be less than 1.12. As the density is 1.61, I assume it cannot be in equilibrium mode. Are the Cassini team expecting to get measurements of the gravity field, especially the harmonics from the recent flyby? I imagine that if we can calculate accurate models of the interior, this may help solve the problem of where the energy is coming from to drive all the surface tectonics. Going slightly off at tangent, I have been perusing the incredible images from the flyby,and it is amazing that this is all happaning on such a small body.

7/20/2005 12:10:00 PM  

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