[X] My Assistant

[Palomar]

Tiny Enceladus May Hold Ingredients of Life Yep, Titan's having to share the spotlight.

*A friend wrote the following to me privately yesterday, regarding Enceladus:

In the absence of a better idea from any quarter, I wondered about a large rocky meteor perhaps having impacted Enceladus at that anomalously warm point some time ago, burying itself in the moon's icy crust. The radioactive elements in the meteor, decaying over geological time periods like a lesser version of the ones powering volcanism in Earth's interior today, might be producing just enough heat to melt a deep portion of the crust, causing the outgassing, and elevating the surface temperature by the observed 20 deg.K.  That same relative warmth, softening the frozen crust, might quickly have erased the crater which resulted from the collision and removed the tell-tale evidence of the meteor's existence.
         
Being a comparatively rare event, an impact like this would explain why Enceladus alone has a hotspot while other icy moons of a similar size are uniformly cold and geologically dead, as we would expect.

It's an understatement to say that's an extremely interesting speculation.

-Cindy

[Guest_Richard Trigaux_*]

What I think is that what we saw on Miranda and what we see on Enceladus is the same thing: diapirs of warmer ice upwelling from the interior and doing these strange drawings on the surface. On Miranda, it is long ago cooled and craterized, on Enceladus we have the chance to see it active.

Why a hot spot, and not a volcanism all around the planet like on Earth? Likely because these bodies are much smaller than Earth, with lower dimention and lower density: so when a source of heat arises in the interior, it forms an unique diapir (eventually several in history, but only one active at a time). As if the hotter core was popped asides like the pit of a cherry. So there is no need to suppose that there is something special at the place where it appears.

The real mistery is what was heating the core of Enceladus or Miranda, and let it cool, and heat it again, several times as far as we can see. Not radioactive heating, it is a one time process. Not impact, it generates heat only on the surface. The only remaining candidate is tidal heating. And there can even be a delay between the tidal heating and the appearance of the diapir at the surface, or the tidal heating being constant and diapirs appearing at times.

The other lesser mystery if the appearance of large boulders on Enceladus surface.

Another open question is why the lesser icy moons have geological activity, where the larger have not. we should expect the countrary.

[JRehling]

Another open question is why the lesser icy moons have geological activity, where the larger have not. we should expect the countrary.

If two moons have the opportunity to tug on each other's orbits, it is the smaller one that receives the larger eccentricity and therefore greater tidal flexing and heating. This is much like why, among almost all of the planet-satellite pairs in the solar system, it is the small body that has been the tidally-locked one. Jupiter plays havoc with Io, but Io barely affects Jupiter.