Livable Exomoons?

So let's toss this out for consideration...

In light of the movie, "Avatar," which is set on the life-bearing satellite, "Pandora," revolving around the gas giant, "Polyphemus" in the Alpha Centauri star system, we are given the usual scifi plot of the moon being habitable instead of the gas giant planet proper. (This was also done in the Star Wars movies with the moon, "Endor.")

If we were to create our own moon around our own giant planet, in our own star system (our own and a creation since we humans have yet to actually find a satellite orbiting a planet outside of our own solar system) what would need to be the parameters for life? (I may not have a continuing path of thought here--I may go off on a certain tangent that strikes my fancy and pick at it, forsaking the rest of the original thought. Bear with me here. I'm just idea bashing. Might use them, might not.)

It would have to have a mass close enough to Earth's own to retain an atmosphere primarily--unless we took the route of another form of life that did not need breathable gases to support its life--perhaps some type of photosynthesis that pulls nourishment directly from the rays of its star and capable of living in vacuum? But I'll leave that for another day--if ever.

So we're massive enough to retain a breathable atmosphere. Is it so massive that it is able to scavenge atmosphere from its gas giant planet? Is the mother planet giving off radiation? If so, the atmosphere would have to be thick enough to protect the life forms from the ambient radiation.

Next, do we have a rotation? Or is the exomoon tidally locked? One side always facing its planet? Imagine this, for a moment--a set up similar to our own moon. Depending on the circuit around the planet, and thus the star, one side would always be warm (warm only--not superheated. We want life here, not cinders) and the other always cold. Well, not always--but for a lengthy measure of time. The transit time of dark to light would vary depending on how long the lighted side was facing the star. Would we get substantial winds as the warm and cold air fought along the shadow-line? How substantial could they be and still have life develop? Would the life forms be low to the ground? Or just massive? How would the life develop to deal with the high winds? Or would the life forgo surface dwelling altogether, returning to the sea and gills?

Let's go the aquatic route. They never stayed on land due to the high winds. They remained aquatic. So we now have a set of aquatic denizens on our exomoon that have now become sapient and are in the process of discovering space flight. Of course they are after space flight. We don't want a puddle of tadpoles, swimming around. There's no story in that. (We'll skip the long trek out of the stone age into the industrial age for now.) How cold did the dark side get during the night. (Let's make the "days" and "nights" last 4 months for each portion, for a total 8 month long day/night cycle, just to pull a number.) Did the oceans freeze over during the night? We obviously would not have a fire-based launch system living underwater. Would they even be able to launch from beneath the surface? Since they did not stay on the land during their climb from stone age to technology, it would seem so. But that gives us a new set of problems. We now have to reach escape velocity through the water and through the air.

Let's have the oceans freeze at night. Not solid, but enough of a crust of ice that "Launch Window" takes on a whole new meaning. It's not whether or not we have the proper trajectory to reach our target, it's whether or not we can break through the ice.

What other problems will they face? We're not just launching our life form's mass. They will also have to bring up their "atmosphere" too. In this case, we're talking enough water to breathe. They live underwater, of course they are going to breathe it with gills.

One gallon of water on Earth weighs 8.35 pounds, making a five gallon jug weigh 41.75 pounds. Without going in to the difference in gravity from Earth to our exomoon, let's just think about the mass of all that water.

Quick experiment: get a one gallon jug of water and a five gallon jug of water. Put both of them on the floor. Balancing yourself on on foot, push the one gallon jug with the other foot. Now push the five gallon jug with the same foot. See the difference? Imagine now the amount of water needed to "breathe" for any extended space trip. Imagine now the amount of force needed to lift it off-planet (or off-moon as the case may be). Are we delving into the realm of diminishing returns here? Mass of life forms, plus mass of space ship, plus mass of ship's drive, plus mass of water, verses delta V to break out of the gravity well.

And once we're clear of the exomoon's gravity well, we have that of the gas giant it orbits to deal with. We'll also have that of the star--be it a single, or a binary (like that in "Avatar").

Are they so advanced in mathematics as to create a star drive that does not require fire? One that would lift all this mass? Through the water resistance?

Or am I poking sticks in the wrong mud puddle? Are they truly just happy sapient tadpoles, ignorant of the stars and space? Will they simply be happy swimming in their oceans, thinking artistic thoughts and occasionally poking their heads out of the water long enough to lick their eyelids and decide that this is not for them?

Tadpoles . . . juvenile lifeform that later crawl out of the mud and walk erect to tackle space and fire and the atmospheric wind? Naw, we already decided that they gave up on the wind. So we're back in the mud.

Let's give them a drive that can do what we need: lift the froggies, along with their breathable water, and their starship. Since we're just idea-storming at the moment, let's just call it the "Tadpole Drive." Somehow it mathematically waggles its forcefield tail behind the ship and swims it up through the water, and through the air--and is capable of doing the same in vacuum. Alas, it is slow, in star distances. So once they are clear of the water, they have to switch over to some type of star drive.

For the sake of argument, we going to decide that they have found that the light speed boundary is able to be broken. They discovered the mathematical calculations to show that it can be passed. (Hey, speed of sound used to be unbreakable, too!) No hyperspace here! Nosireebob! They have a good old fashioned zoom along drive!

They're first ship must have met with a horrific end. Not knowing about all the particles that are out there, they would have plowed into one and bam! Fireball! Imagine the energy released by two objects colliding at faster-than-light speed. One, a starship of . . . let's say the size (mass) of a 737--filled with water instead of air, of course. The other, a grain of sand. Imagine a particle collider . . . with our froggies as one of the particles. Boom.

So our humbled froggies go back to the drawing board and come up with some type of magnetic field (I'd hate to call it a force field, but along that idea) that will deflect particles and such from the path of the starship.

But wait--let's back up. How did they even discover about space and stars? They're aquatic, after all. At some point they would have to brave the winds to look unblinking into the night sky and wonder at those bright points of light. And with a gas giant as the mother planet their exomoon is orbiting, conditions would have to be just right for both the sun and the gas giant to actually allow a star watching night sky.

So the conditions were all perfect, and Froggy went a gazing and he did spot a star. Uh, huh. Being curious creatures, they decided that they wanted to travel to these pinpoints of light. But wait (there's more!) the traditionalists fight them. If Froggies were meant to star travel, the Great Egg On the Surface would have given them fire erupting from their hind end--not tails.

We would have a great conflict between the two factions. They would most likely be omnivores. So meat is on the menu. Why? Omnivores and carnivores are feistier than herbivores. We don't want herd beasts. We want individuals that will have that spark of fire that drives one being to overcome another.

So how would the fight go? Would it be mostly rhetoric with occasional bellowing matches? For that matter, how would they communicate? Color changes on their skin in a manner similar to that available to the octopus? Voice is right out the submarine's window...

We'll select color changes on the skin, supplemented by scent emitted into the water. So we have a stinky Technicolor battle of ideals going on under the sea. The seas are shallow enough for light to permeate, but deep enough for their cities. Perhaps along the lines of the crystal clear waters in the Caribbean? C'est bon. We'll leave them flashing and stinking for now, and pick it up another day . . . maybe. I don't like the smell of day-old fishy things.