Hypothetical Ocean on Gas Giant Moon

[nithska]

Hello there,

I am working on a story that is an extrapolation of something I once read about one of the Jovian moons possibly having an ocean that essentially follows Jove across the face of the moon in one big bulge of water. Another thread on the forum talks a bit about this concept, and that the tide on an ocean on a moon of a gas giant would have actually two high tides bulging toward and away from the planet. I know it is more complex than that, and answers of great complexity are good! :)

Here's where I'm going with this:

I'd like to set my story on such a moon that has the following parameters:

Earthlike in temperature, though the planet can range in size from luna, mars to earth equivalent as would make sense from perspective of orbit being close enough for an ocean having the above tide characteristics, but not stuck in the Giant's Van Allen Belt.

Last, I'd like to have a valid reason for the low tide to be near nothing: a few inches of water to two feet max, whereas the higher 'high tide' is, the better. Also, can you think of a valid explanation for high tide to be composed of a series of increasing 'bulges' with troughs between like sine waves, I guess. MIght a moon around the oceanic moon cause this?

Please accept my humble thanks for any thoughts you might and when I sell the story I will offer credit for any help I get.

Take care,

Brandon

[Paul Beardsley]

Hi Brandon

Welcome to the board.

I think the moons of gas giants are fertile ground for stories. It occurred to me that if they get their heating from tides, then they don't actually have to be in orbit around a sun - they could be in deep space.

I take it from your description that your moon is not tidally locked? If it is always presenting the same face to the gas giant, the only tidal bulge it would get would be from the sun, and other moons.

You could have several moons which regularly synch up and combine their tidal effects, then separate again.

I'm guessing the few inches of water to very deep is a reasonable scenario. Maybe not across the whole moon, but significant parts of it. I've been considering a slightly similar idea for a story for many years but never got around to writing it.

Have you sold any other stories?

[timb]

Hi Brandon

Welcome to the board.

I think the moons of gas giants are fertile ground for stories. It occurred to me that if they get their heating from tides, then they don't actually have to be in orbit around a sun - they could be in deep space.


I don't believe that tidal heating would provide much heat.

[nithska]

Paul,

Wouldn't the ocean 'bulge' toward the gas giant? And yes, I can't have it tidally locked since I'm looking for the ocean to essentially travel across the face of the moon, the high tide of the ocean being locked to the gas giant. (and away from the gas giant I have read) ?

Also, how large could this bulge be? Is there a way to reliably calculate this?

Thanks again.

B

[BigDon]

I don't believe that tidal heating would provide much heat.

Isn't like what keeps Io molten?

[Paul Beardsley]

Wouldn't the ocean 'bulge' toward the gas giant?
There would be two bulges - one towards the gas giant and one away, as you say. Just as on Earth, there's always a water bulge towards the moon, and one away from it.


Also, how large could this bulge be? Is there a way to reliably calculate this?

I don't know, but I'll be interested if anyone else does.

And as I said, tell us more about your writing. Is it your first time, or do you have a few publications under your belt? Have you just started writing, or have you been at it for years? Do you just write space stories, or are you more diverse?

I'm sure everyone will be interested as there are a lot of writers (and readers!) on BAUT.

[Paul Beardsley]

Isn't like what keeps Io molten?

I believe it is. Again, I'd like to know more - for instance, is there some simple equation that just requires you to square the distance between the gas giant and its moon, add the planetary masses, and do some other things that aren't too complicated?

[timb]

Isn't like what keeps Io molten?

Possibly, but Io is not a moon that orbits outside Jupiter's "Van Allen Belt".

[Paul Beardsley]

Possibly, but Io is not a moon that orbits outside Jupiter's "Van Allen Belt".

But presumably the size of the Van Allen belts can vary. We know there are much bigger planets than Jupiter in other solar systems. Maybe they don't have to have correspondingly big VABs.

[Disinfo Agent]

I'd like to set my story on such a moon that has the following parameters:

Earthlike in temperature, though the planet can range in size from luna, mars to earth equivalent as would make sense from perspective of orbit being close enough for an ocean having the above tide characteristics, but not stuck in the Giant's Van Allen Belt.Are you thinking of an underground ocean, or the whole moon, when you speak of temperature?

Suggested reading: Arthur C. Clarke's novels 2010 and 2061. His short story Jupiter V (loosely related).

[nithska]

Thanks for all the thoughts so far...

Paul,

I missed your question the first time. Sorry! :)

My short stories can be read in the Hadley Rille/ National Space Society Return to Luna Anthology (my story is called Best Gift), M-Brane SF issue #1 is available for free online and features one of my stories and I have another coming out in M-Brane SF #5 (I think: it will be in a recent issue at any rate). I also have a story in the Byzarium August 2008 archives (which is going to be taken down soon, so I highly recommend checking out Byzarium in general if you like reading SpecFic... while you still can!), and I also have three honorable mentions in the 2008 SpaceWesterns.com senryu contest (still online last I checked.)

Anyway, my fiction tends toward SF, and I love a good space-faring tale, which my forthcoming in M-Brane and the Return to Luna both are examples of. Best Gift is the only true Hard SF I have written thus far in the sense that I actually address the science behind the subject matter (in that case, moon domes, space suits, and 'neodramadaries' sp? augmented with cyanobacteria), but even if my more 'new wave'ish stuff, I try to 'play by the rules', i.e. observe physical realities.

Which brings me to my present tale, which -if I can get away with it- will be called 'On the Demise of Captain Fantomas Patton-Guerrero and Loss of La Amenoza Elegente'. This is a novel set a bit farther into the future of Best Gift and my forthcoming M-Brane SF story, but a bit more swash-buckling/adventurous.

<puts away his 'own horn'> :)

So here's the deal though: despite Best Gift being one of my shortest stories, it was a hard thing to write because, based on the audience, I had to get the science correct. I want to achieve the same with this story.
------
Disinfo Agent: No, I am looking for a surface ocean. This means the gas giant would need to be closer in to the star, and I assume based on this, it would be either occluded white with water or ammonia clouds, or deepest blue if the clouds are burned off from nearness to the star.

Also, not to get sidetracked, but what are the chances that Rigel Kent, aka Alpha Centauri A has a gas giant in the habitable zone?

------

I'm hoping I can rationalize the planet-facing bulge to be a series of bulges starting with what we might typically think of high-tide in layman's terms, then bulge after larger bulge culminating in the giganto of sea bulges.

I'm envisioning that final greatest bulge as something akin in height to Everest, though possibly more broad than that, with troughs between it and the next smaller bulges to either side (trailing and leading bulges).

Fantasy trying to look like science, or can anyone suggest a rationale for this?
Thanks again!

B

[Disinfo Agent]

Disinfo Agent: No, I am looking for a surface ocean. This means the gas giant would need to be closer in to the star, and I assume based on this, it would be either occluded white with water or ammonia clouds, or deepest blue if the clouds are burned off from nearness to the star.Yes, and you are likely to get a wider temperature range than on Earth, since the moon revolves around another planet in addition to orbiting its sun.

There may be a problem with the atmosphere. Is it plausible that a moon with a sizable atmosphere would form that close to the sun? Or would the gas giant tend to absorb most of the gas as the solar system was forming? I really have no idea.

The tides would probably be more impressive than on Earth, I think, since the gas giant would be much larger than its moon.

[nithska]

I guess the questions in order of importance:

1) how impressive can the realistically portrayed tide be, given the parameters?

2) could the tide be only a typical solitary bulge (or two bulges, one toward one away from the planet), or is there a rationale for a series of increasing then decreasing 'bulges?

3) do we know there are no Jove-like planets close around Alpha Centauri A or B, or does that remain a possibility?

If I can wrap my brain around these three big points, I can probably rationalize the finer details (Van Allen belt, atmosphere formation, temp, ect.).

-------> any suggestions on other resources I should look into are welcome. I'd love to find some programs that let me play around with orbits/tides etc, though I know that is probably a long shot. I use Ubuntu, btw, but can run windows programs most of the time via crossover. b

[BigDon]

Possibly, but Io is not a moon that orbits outside Jupiter's "Van Allen Belt".

Wow, not what I thought I was going to find when I read the wikipedia article on Io. The interaction of two other moons is what keeps Io molten. Io wants a circular orbit around jupiter but the other two large moons force Io into an ecentric orbit thereby causing the frictional heating from flexing with the tides.

Who'da thunk it?

[timb]

Yes, and you are likely to get a wider temperature range than on Earth, since the moon revolves around another planet in addition to orbiting its sun.


Why? I don't think the variation in distance from the sun would be significant. The moon-planet might cool down during eclipses, but how long would they last?


There may be a problem with the atmosphere. Is it plausible that a moon with a sizable atmosphere would form that close to the sun? Or would the gas giant tend to absorb most of the gas as the solar system was forming? I really have no idea.


Under the popular core accretion model, gas giants don't form that close to its sun. It would have arrived there by migration. Moons would either have come along with it or been captured during migration. Would original moons survive migration?


The tides would probably be more impressive than on Earth, I think, since the gas giant would be much larger than its moon.

If its rotation were synchronous, which is the case for all the large moons in the Solar System, then its tides would be due to its sun only. Massive tides implies massive dissipation implies rapid synchronization. That seems to be the main problem with the OP's scenario, that and the technical difficulty of arranging the pattern of tides he proposes. Coming up with a model would be work I'm not inclined to do for someone else's profit.

[Paul Beardsley]

If its rotation were synchronous, which is the case for all the large moons in the Solar System, then its tides would be due to its sun only.
And also its sibling moons.

[timb]

And also its sibling moons.

Do you have a stable orbital model where they raise massive tides?

[timb]

Do you have a stable orbital model where they raise massive tides?

"Massive" needs to be quantified. I think significantly greater than the moon's tides on Earth is possible, for close-in satellites.

[Paul Beardsley]

Do you have a stable orbital model where they raise massive tides?

No, but from what BigDon said about Io, I would guess it is the case.

[nithska]

Timb,

Sorry to leave a bad taste ... as a 'little guy' in the publishing field, a first novel will net a few k in advance with an average life-time earnings of up to 10k, generally speaking. But I am getting way ahead of myself, as it could be that the book never sees the printed page.

Any general thoughts would help, though I don't want anyone to feel put upon. :)

B

[Van Rijn]

I strongly recommend you read Rocheworld by Robert Forward. That was a double planet, and he did have very large ocean tides (it helped that the worlds were so close together).

[chornedsnorkack]

It is kind of difficult to have strong tides and unlocked free rotation, because of torque delivery by tidal friction.

That said, you might have 3:2 tidal lock, like Mercury. For an eccentric orbit.

[timb]

It is kind of difficult to have strong tides and unlocked free rotation, because of torque delivery by tidal friction.

That said, you might have 3:2 tidal lock, like Mercury. For an eccentric orbit.

Mercury's tides are tiddlers. For one thing there's no water. The dissipation is far greater in oceans, especially ones that run up against continents, than in rocks. Tidal dissipation tends to circularize orbits too, though some degree of eccentricity can be maintained by perturbers.

Io and Ganymede should both raise significant tides in Europa. The tidal forces attributable to each at their closest should be larger than those imposed by the Moon on Earth.

[cjl]

Do you have a stable orbital model where they raise massive tides?
No, but due to orbital resonance, the other moons can cause a somewhat eccentric orbit for the moon. This would cause fairly sizable tidal variations between apoapsis and periapsis due to the giant planet itself.