Just the way you can rub your hands together on a cold day to warm them up, the process of frictional heating can warm up an object in space. We see this through Jupiter's interactions with Io, and now, astronomers report, that's the same process that's causing geysers of ice to erupt on Saturn's moon Enceladus. ...

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Same process as Jupiter's interaction with Io?

guess they forgot the How many watts to "boil" water ?

eccentricity??? Now I read somewhere bodies moving on eccentric orbits displayed some unusual properties.


surely they couldn't be saying they may have a common cause for both phenomena? Are they? Is it tidal flexing, radioactive core maybe mixed in with some "organic stuff" or indeed the same as Io?

Interesting discussion HERE

What puzzles me is, how long can such a procees run whithout dying out? How old are Enceladus, Io, etc? Four billion years? If so, does this allow for the proposed processes?

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Exactly the same process, yes.


No, because there isn't a flux tube between Saturn and Enceladus.


Yes, they are. The eccentric orbit is what causes the heating - it's all down to the fact that the satellite is repeatedly getting closer and further from its massive primary. It doesn't matter if the primary is Jupiter, Saturn, or anything else - so long as that eccentricity is maintained, the heating will continue. In extreme cases, it's enough to melt significant amounts of the rocky material inside the planet (as it does on Io) - in less extreme cases it just melts ice (like on Enceladus and the other Galileans satellites).

To answer dhd40's question, the key is that the eccentricity must be maintained. Left on its own, the heating would cause the satellite's orbit to circularise, and when it's fully circular there'd be no more tidal heating. But in a system with other satellites (like Jupiter's or Saturn's), those satellites can give eachother regular gravitational tugs (particularly if they're in resonances) that keep the orbit eccentric.

It's like being on a swing in a playground. If just give one push, then the swing eventually stops swinging. But if you keep on pushing, the swing continues to swing as long as that's maintained. If you keep on pushing regularly, then that's similar to what an orbital resonance is.

Other things like electrical heating from flux tubes, or radioactive heating from decay in the interior also contribute, but tidal heating can be and often is much greater than either of these contributions.

Orbits will never perfectly "circularize" (there is always some eccenticity) so the heating may continue. Remember, the Moon travelling around it's orbit continues to affect tides on the Earth.

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The Earth is bi-polar.

That's a non-sequitur. Yes, orbits in reality are probably going to have some small residual eccentricity if there isn't anything else there to keep it forced at a higher value, but it can still end up so small that there's no tidal heating. Triton - Neptune's big moon - originally must have had a high eccentricity when it was captured but its eccentricity now is 0.000016 (which is VERY low in solar system terms - even the orbits of the innermost asteroidal moons of Jupiter - which are subject to a lot of circularisation - are more eccentric). You can see the effect the tidal heating had on its surface in the Voyager 2 images - huge areas are resurfaced completely - but that heating isn't happening anywhere near as strongly anymore because the eccentricity is so low (that said, Triton's inclination is pretty darn high, but I don't think heating resulting from the orbit moving into the equatorial plane is as bad. I am admittedly a bit fuzzy about that).

But that has nothing to do with our moon raising tides on Earth as it moves around it. That happens because the moon's orbit is eccentric and the earth is rotating. But when the moon's orbit circularises, and the earth becomes lock to the moon (which won't happen for billions of years, if we don't lose the moon from orbit altogether before then) then the tides won't happen anymore.

I figured that tidal action similar to what happens with Io was responsible for the moon's heating (could I pull a Hoagland, and claim that I thought of this first? ). Interesting.

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This is really interesting. I would have never though of that working. I mean i know that a comet is heated by friction as its coming into the solor system but a planet or moon...i think thats really cool.