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This may belong in "Against the Mainstream" because it's rather speculative, but it's still an interesting CETI problem.
Europa is heated by its other moons forcing it to have a somewhat eccentric orbit, and thus, variable Jovian tides, though this heating is not as strong as Io's. It is enough to enable its surface to be re-created very recently by geological standards, as the paucity of craters on its surface indicates.
This heating implies that there may be hot springs at the bottom of its ocean, and maybe prebiotic chemistry and even life. The primary producers would likely be methanogen-like microbes; there may be others that live off of these.
However, there may not be free oxygen, meaning that metabolism of consumed prey would be limited to fermentation, which is relatively inefficient. This may preclude the appearance of macroscopic animal life, such as tube worms and plankton-eating filter feeders.
This makes sentient life unlikely, but it is nonetheless intriguing to speculate about "Europan dolphins", as I decide to call them. Though "Europan octopuses" might be a reasonable alternative for a sentient inhabitant to be.
They would be blind, since there is almost certainly no light in Europa's ocean, but they would have well-developed hearing and would use echolocation (sonar) rather intensively. And they would also be very talkative.
Contacting them would be a serious challenge,since they would likely prefer to live in the lower depths of Europa's ocean, where the hot springs are. This means that one would have to send a submarine *very* far down. For safety's sake, it is best that they be robot subs, at least initially.
Let's imagine approaching a pod of Europan dolphins; they would not be able to see the sub's headlights, but they would hear its odd sounds and its odd sonar signature. The dolphins would look white, because there would be no adaptive value in being pigmented.
One serious communication problem is the lack of a clear "Rosetta Stone" such as pictures; however, one could create a Braille equivalent of pictures on a flat surface by putting small rocks on it or by dragging a robot arm on it if it is sediment. A Europan dolphin may still find it difficult to understand, but a Europan octopus may have more success, because it could feel the Braille picture with its tentacles.
Clearly, all we would have to do is play old Abba recordings for them.
Just how variable is the environment. What would the tides do? Not that much, to the surface, right?
I think that heat sensors may be more widespread than sonar. Life, and therefore prey, would cluster around hot springs, and you can't find a hot spring with sonar alone.
Just out of curiousity, are there any other marine lifeforms other than dolphins and whales that use sonar? It seems to be a strictly mammalian thing, even then, it's not common.
The "heat column" above a hot spring would be as "visible" to sonar as smoke from a fire is to us.
Was I the only one that, upon reading the title of this thread, thought "What's up with the dolphins in Europe?"
Now that I think about it, I've never had mahi-mahi in French restaurant.
Just FYI, mahi-mahi is not (mammalian) dolphin. It's a kind of Pacific Ocean fish that is also called dolphin in some areas. It's the same genus as the fish known as "dorado" in the Atlantic.
I think it's a bit more than "speculative," though it sounds like a decent setup for a science fiction novel.
but it's still an interesting CETI problem.
Europa has no "other moons." I assume you mean Jupiter's other moons...however, the other moons have very little effect with regard to tidal heating on/in Europa or the shape of its orbit.
It is Jupiter itself which is responsible for the tidal effects which are heating up Europa's interior.
As for the rest of your speculations, you are building conclusion upon conclusion...one idea being the precursor for the next. This makes for a rather unlikely chain of dependant events. By the time you get to Europan dolphins, it's pretty much fantasy.
First, I wish to apologize for not having described the source of Europa's heating more carefully; I did have in mind Jupiter's other satellites when I described the source of the perturbations of Europa's orbit around Jupiter.
And Gregory Benford may have followed my line of reasoning in speculating about Europan sonar users. Electric-field sensing is certainly a possibility, but like touch, it is relatively short-range.
There is one possible source of light in the Europan ocean: chemiluminescence from hot springs, which has been observed near ocean-floor hot springs. But that is likely to be very weak, meaning that there would be little impetus for vision to develop beyond a simple light-meter sense.
the other moons have very little effect with regard to tidal heating on/in Europa or the shape of its orbit.
That's only half-true. Europa (and Io, for that matter) are heated by the rising and falling of its Jupiter-induced tidal bulge. That bulge rises and falls, instead of staying the same height, because Europa's orbit is somewhat elliptic - when Europa is farther from Jupiter, the tidal bulge falls and when it is closer, drops. However, that process tends to circularize Europa's orbit - indeed, the heat energy ultimately comes from Europa's orbital energy, thus lowering Europa's aphelion. Without other moons, Europa's orbit would quickly (in geologic terms) become a circle, and the heating would stop. Perturbations from other moons keep Europa's and Io's orbits elliptical.
Gravitational interaction between moons can not change their total orbital energy, and the tidal heating removes some of that energy. Hence the overall effect is that Europa and Io (and possibly Ganymede and Callisto) are very slowly spiraling toward Jupiter. After many billions of years, probably longer than Sun will shine, Io will reach Roche limit and will get torn apart into a spectacular ring. Still more gigayears later, so will Europa.
Just for the record, Benford's book was called "Across the Sea of Suns".
The dolphins would look white, because there would be no adaptive value in being pigmented.
Mmmm, maybe, maybe not. There could be several sources of (albeit dim) light.
1. Deep in the Earth's oceans, you have many creatures that produce bioluminescence. Even the surface algae produces a glow sometimes visible when the water is disturbed by crashing waves.
2. Volcanic fissures could glow red hot.
3. If I'm not mistaken, photos show evidence of the surface ice cracking in many places. If the cracks ran clear down to the ocean level, a little sunlight could be let in before the surface re-froze. Imagine an ocean teaming with algea spores that float dormant for years, waiting for the moment they are in the right place at the right time when a crack in the ice appears overhead letting the distant dim sun to pour its engery into the black waters. They quickly come alive for however many hours or days it takes for the ice to again form thick enough to block the life-giving photons. Then they go back into a stage of dormancy, slowly anaerobically feeding off their stored energies until the ice again parts overhead.