Very interesting...

"Cassini Data Show Ice and Rock Mixture Inside Titan "
http://www.jpl.nasa.gov/news/news.cfm?release=2010-084

Interior like Callisto, exterior Earthlike.....

Hmmmmmmmmmmm......

Craig

I find this very exciting. Kinda like another paradigm buster.

Many of us living in the pre-Voyager days were blinded by the inner terrestrial planets and how they seemed to 'work'. Tidal heating as a source for pumping up the geological activity was purely theorectical. Until the Voyagers blew us all away with what we saw at the outer planet moons.

Here we have Titan, a Callisto sized moon with a Callisto-like interior (not completely differentiated), but with signs of very active geologial processes at the surface.
Perhaps it is the mix of more volatile materials like methane that make the difference.

Whatever makes the difference, it bodes well for activity on other "undifferentiated" worlds.

WOW.. love this.

Craig

Putting all the big moons in perspective:

Titan: PIA12843

Galileans composite(Io, Europa, Ganymede, Callisto): PIA01082

Individual Galileans:
Io: PIA01129
Europa: PIA01130
Ganymede: PIA00519
Callisto: PIA01131

Hard and crunchy on the outside, soft and chewy on the inside...with a subtle flavor of raspberries and bitter almonds...

How puzzling and unexpected (at least to me!) I wonder, then, if the energy source driving Titan's active surface is directly (and solely) related to the apparent decoupling of the crust from the mantle.

Craig's got it right, though...wow. The diversity of the Solar System continues to astonish!

Yeah Nprev... surprised me too!

Not what I expected at all given the surface activity. Nature is just way more imaginative then we are.

I wonder is there is a way that the more volatile elements like methane somehow got concentrated at the surface in the later stages of Titan's formation?

Mike... hard and crunchy on the outside does not mean dead on the inside or vice-versa. Surfaces that are disconnected from interior processes or lack of same?

Craig

I feel like more people ought to be tipping the hat to Jeff Moore for his provocative (and prescient?) AGU talk "Titan: Callisto with Weather?", presented in December 2008.

I'd forgotten that. FWIW from the likes of me, hats off to Jeff!

One thing, though: That massive atmosphere doesn't maintain itself, not with such a gentle gravitational grip. There is some kind of long-term outgassing mechanism, and therefore an internal energy source..."internal" in this context meaning 'somewhere below the surface at an unspecified depth'. Almost certainly tidal IMO, question is exactly how & where given a cold, undifferentiated core.

Time to check for methane slowly oozing out of Callisto?

I do remember that paper by Moore. Actually my worry before CASSINI was just that. Titan would be a Callisto with air. Some spotty crater lakes overlaid with smust.

Now if Titan does outgas methane, question is, as nprev pointed out, what powers this internally?

Very interesting....

And fascinating!

Craig

How much do we really know about the mobility of methane within high pressure dirty ice mixtures? Couldn't it just slowly diffuse through the mass at temperatures well below that needed for ice/rock differentiation? That possibility could be tested at Callisto.

I prefer the concept "Titan: Earth without the Drama"

One puzzle to me is that Titan (and the other large, undifferentiated icy-rocky moons) remains undifferentiated. Even with no internal heating, the difference in specific gravities (one vs two-ish, approaching three) so "some settling" ought to occur. And ice, being a supercooled liquid, flows and deforms over time at terrestrial temperatures, and presumably cryogenic temperatures. And I've no idea how high pressures, such as found in large icy worlds, affect the physical properties of ice. And no idea of how a methane-clathrate behaves at "subterranean" temperatures and pressures.

Truly, alien worlds.

--Bill

IIRC, the quote I remember is that Titan is about "40%" differentiated. So it started, but just didn't go all the way to having a molten core.

Under pressure, water ice can exist in other crystalline phases (Wikipedia/Ice#phases). The layer beneath the subsurface ocean is thought to be other (non-Ice(I)) high pressure phases of ice. Having a different (more compact) structure, these can have a higher density than water.

(So, ice(1) crust > ocean > high-pressure ice phases is a stable configuration)

I would expect the size of the silicate particles to have a huge effect - if most of it is in the form of dust it might not settle without complete melting of the ice. And as Mike mentions we're in a world of weird ice phases. Not just the theoretically understood water ices 1,2,3 etc. but multifarious impure phases as well. I have always been sceptical of published accounts of the thermal and compostional evolution of Titan's interior, some including quite detailed histories. The models make fascinating reading but there is always a sense that the gaps in the data may be just too big still.

I find it somewhat hard to believe. How radiogenic heating of such a big volume of material managed to escape through its surface - especially considering a thick layer of atmosphere over it?