Extreme Planetary Features vs realism

[Chick]

If a gas planet (like Saturn) migrated close (but not too close) to a star (maybe the size of Alpha Centuari), would it be viable for the moons of this gas planet to absorb gases from the planet similar to the companion effect that impacts stars? If the Gas Planet had plenty of Oxygen and Nitrogen, could it be possible for life to be sustained on these moons?

Not impossible if there were any reason for the gasses to migrate from the planet to the moon, but I can't think of why/how that would happen.

Could the atmosphere of a gas planet comprised of oxygen (primarily) extend beyond the moons, which if solid and contained enough water, produce or sustain life?

Impossible, due to Roche Limit, as Azelor said. http://en.wikipedia.org/wiki/Roche_limit

All of that said, there is no inherent reason that the moon of a gas giant couldn't contain an atmosphere, and if within the habitable zone of a star, liquid water and potential life.

Consider Titan, satellite of Saturn, which contains an atmosphere denser than Earth's, and Europa, satellite of Jupiter, which is suspected to contain liquid water beneath the ice surface (melted by gravitational friction due to Jupiter's proximity). If either of these were in the habitable zone of Sol, they might well be habitable.

[Soloeus]

I see.

One of my "Colony Worlds" is a gas planet approx the size of Saturn, which contains 5 moons. 1 moon is aquatic, 2 moons are capable of hosting life (but did not evolve anything beyond vegetation). Since those living there are colonists, I can assume that would be okay. I am glad I don't have to go out of my way to handwave why the moons of a Gas Giant could contain life.

[Chick]

Just put the primary (planet) in the habitable zone of the star and you should not get any complaints

It's true, as JohnVanVliet pointed out, the moons would be tidally locked to the primary (meaning they always keep the same side toward the planet), their revolution around the planet would expose the other sides to the star (sun). So you would expect to have a portion of the planet-facing moon surface that was not exposed to sunlight, and the rest of the moon having unusual cycles of sunlight, but your story can probably deal with that.

[Soloeus]

Just put the primary (planet) in the habitable zone of the star and you should not get any complaints

It's true, as JohnVanVliet pointed out, the moons would be tidally locked to the primary (meaning they always keep the same side toward the planet), their revolution around the planet would expose the other sides to the star (sun). So you would expect to have a portion of the planet-facing moon surface that was not exposed to sunlight, and the rest of the moon having unusual cycles of sunlight, but your story can probably deal with that.

Indeed, a difficulty for the colonists who live there. I am creating a local sector map (part of alpha quadrant of this galaxy) which will feature different stars that have qualified planets for life. What surprised me from a little more searching is how rare such a Star is. Too big and the lifebelt is bombarded with lethal radiation. Too small and the life belt would be too close to the star and the planet would not be very stable. I want the things I use to be believable in the sense that it could happen without having to stretch too much.

Thank you all, by the way, for using your knowledge to help those of us who lack it. I did take an Astronomy class but it was an online class and the real thing I learned is that I don't learn in that kind of environment. Not my cup of tea, which is a shame because the course is only offered online in my region.

[johnvanvliet]

t's true, as JohnVanVliet pointed out, the moons would be tidally locked to the primary (meaning they always keep the same side toward the planet)

not one sided

the moons are locked ( AND ROTATING) in a orbital resonance

for example pluto's ? moons? are within about 5 to 15% of
Stix has a 1:3 ratio
Nix has a 3:4 ratio
Kerberos has a 4:5 ratio
Hydra has a 5:6 ratio

moons and planets tend to fall into the 1:2:3:4:5:6:7:8..... orbital ratios

earth and mars are close to a 1:2

getting a planet or moon to be " one sided" like our moon is rather complicated orbital mechanics

This resonance is also why large gas giants near the parent star LIKE ( really LOVE) to fling smaller planets out of that solar system
some random googling
--- this is a good game
http://www.stefanom.org/spc/
or
http://astro.unl.edu/naap/pos/animations/kepler.swf
or
http://phet.colorado.edu/sims/my-sol...system_en.html

[Chick]

Depending on the relative sizes and distance, the tidally locked moon might or might not receive much sunlight on the planet-facing side. As we have all seen the full Moon of Earth, the planet-facing side receives plenty of sun, but the Moon is large relative to Earth and fairly far. A closer, smaller moon might be well into the shadow of the planet when that side faced the star.

Here is a nice explanation of some of the factors influencing habitability of a tidally locked planet, and some of it applies to moons.
http://www.astrobio.net/news-exclusi...-inhospitable/

[Trollface13]

well if earth had no moon the orbit would destabilize and all tides would sieze but worst of it is the weather stops then tectonics stop and that means te carbon cycles stop and eventually life on earth as we know it would stop and our blue ball will turn red like mars.... lack of a moon also gives lack of a magnetic field irradiating the planet killing almost all life on the surface.

if earth had 2 moons however its a different story. the extra moon would cause some extreme conditions such as larger hurricanes and vast extremes in wind speed and dust storms it does strengthen the magnetic field but it would also mean more earthquakes and volcanic activity. but really it depends on the moons mass. if its larger than our current one it could rip our planet apart but if it is smaller it would not be so bad.

now earth has had ice ages before and the correct term for tropical age is "Hot House Age" and we had alot of those during the cambrian, carboniferous, and the cretacious/eocene times the Eocene being completely iceless the Eocene epoch was so hot in fact that germany and antarctica were covered in jungles and canada was covered in swamps.

on alien worlds however in terms of climate can vary on atmospheric density and gas composition. take pandora from avatar for instance its atmosphere contains high carbon dioxide levels nearly 20 percent to be exact that is why humans wore masks on the planet as carbon dioxide is toxic to us.... however alternate biologies of the lifeforms on pandora allow the existance of complex life just as long as the 4 biochemicals exist on the planet(oxygen, nitrogen, carbon, hydrogen). however he same climate conditions can be created with an atmosphere like earth just by increasing atmospheric density and/or distance from its parent star. thing is if you want a jungle world in the solar system. reduce the density of venus's atmosphere and filter the carbon and sulfur out and maybe add a few large asteroids as moons you would get the same results as cretacious earth. the reason why the pressure is so high on venus is because of the heat it generates from the surface and sunlight assisted with the carbon compounds in the atmosphere as well as the higher density. but take away one or two of those and you can make many different conditions but maybe not all earth like unless you add a few things too.

as for gravity..... well watch james camerons avatar and look at the trees and the na'vi, they are frakking huge. you know why? because pandora has similar mass to venus. meaning less gravity. if a person is born on the moon and is raised there they could reach about 6 feet at age 10. if a person is born on mars however they would only be around 4-5 feet at age 10.

[Trollface13]

i can list several possible planets that can ocurr naturally in our universe
-Jungle
-Desert
-Ice
-Ocean
-Volcano
-Terran
-Water Vapor Gas Giant
-Diamond

For Jungle & Terran is our own earth as i stated before in the eocene the earth was covered in vast jungles but now its a multiclimate aka Terran.
For diamond if a carbon planet is in eccentric orbit of a sun it can crystalize into a diamond planet after millions of years due to the process of heating and cooling and geological & gravitational friction.
For ice..... well you know what europa is its an ice ball orbiting jupiter plus earth was in a global ice age billions of years ago called "snowball earth"
For volcano we have jupiters Io it is the most volcanically active planet in the solar system.
As for desert.... Mars takes the cake.
Ocean planets are mainly extrasolar superearths. though someday we may find a weird oceanic island planet.
Water Vapor Gas giants now this one fascinated me because these two extrasolar planets are the only evidence that these exist and could harbor floating giant aliens. HAT-P-11b & HD 209458 b both are gas giants containing the 4 key elements for life.

[xpian]

"well if earth had no moon the orbit would destabilize and all tides would seize"
No, the sun also influences tides. Tides would be smaller. I have no idea what "the orbit would destabilize" means.

"the weather stops"
No, weather is generated by Earth's own processes, owing to things like land, sea, and air being warmed by the sun and the planet itself rotating.

"then tectonics stop"
No, plate tectonics on earth have very little to do with the moon. The heat within the Earth, either left over from the planet's formation or generated by decaying radioactive elements, keeps much of the material of the planet below the crust in either liquid or plastic form, allowing huge chunks of solid material called cratons (the building blocks making up the continents) to move about, crashing into each other.

"te carbon cycles stop"
The moon has nothing to do with the carbon cycles of life on Earth.

"lack of a moon also gives lack of a magnetic field irradiating the planet killing almost all life on the surface."
Earth's magnetic field has nothing to do with the moon. Most scientists agree that our magnetic field is generated by the great dynamo at the heart of our planet, the spinning metallic core. Mars, by contrast, seems to have lost most of its magnetic field and the conjecture is that the red planet has cooled off and slowed enough that its core is no longer able to generate one.

"if earth had 2 moons however..."
Some of your predictions are more likely than others, but at least you do point out that the mass of the additional moon is important. To that, however, I'll point out that even a quite massive moon wouldn't necessarily "rip the earth apart". A big moon could fall into a tidally-locked orbit with its planet, one not rotating with relation to the other, both just gently circling for a very long time.

"Hot House Age"
True. Earth has been completely ice-free several times that we know of, when global temperatures and sea levels were both much higher. Also, we've had a "snowball earth" at least twice that we know of, when a runaway albedo effect caused a global ice-age all the way to the equator. If an alien had visited earth in those days, the planet would have looked like Hoth.

[xpian]

"because pandora has similar mass to venus. meaning less gravity."
Venus is Earth's sister world, just a little smaller in size and mass. Surface gravity there is about 91% of what it is on Earth. And we don't really have any good data as to how living things that evolved in 1G would react and grow in 0.9G. Maybe they'd get really tall--maybe not. Maybe it would take countless generations of evolution for organisms to adapt to permanently lower gravity.