Extrasolar Moons: Could There Be Earth-Sized Worlds Around Gas Giants?

[ThomasEdison]

I know that they cannot currently be detected but according to the amount and variety of moons within our own Solar System I would imagine that other solar systems must have a huge number of them.

Although I am not biologist or astronomer (or a scientist whatsoever) it seems fairly obvious to me that there is far greater chance for Alien life to exist on a moon of a large gas giant instead of a rocky world because of the sheer number and variety of them. Also when Io showed volcanism from Jupitor (although that moon is very hot) this shows promise to me for different reasons for volcanism as well as the sheer amount of moons with atmosphere and water.


So I wonder this:
Is there any reason that extrasolar moons have to be smaller than the Earth?

Could it be possible for an extra solar Gas Giant to have several sattelites of approximate size and composition to the Earth; instead of the Earthlike bodies Astronomers are searching for orbiting around the Star?

Wouldn't each Gas giant have its own "Goldilocks Zone" around it?

Isn't a view that the Goldilock's Zone (where liquid water is) overly narrow if it only concerns the Star in a solar system?

Could a Gas Giant beyond a star's Goldilocks zone have one around itself?

What about the electromagnetic Field around Gas giants? Can this field protect the moons in the manner that the Earth's Electromagnetic field protects us?


Here is also maybe an unrelated question:
If Earth's gravity has to do mostly with Earth's mass what about planets or moons of a different composition than our rocky one altogether?

Could a planet/moon be made of material less dense but be larger but retain a similar gravity to Earth's even though it was larger? Is the opposite true also? (or does matter compact down anyhow rendering this idea moot)

 

[mathman]

The main problem for Gas Giants having moons or planets supporting life is their age. Gas giants tend to have relatively short lifetimes, so chances of life evolving in such a system are small.

 

[Vanadium 50]

Mathman, that puzzles me. Isn't Jupiter the same age as the earth?

 

[russ_watters]

...confusing giant planets with giant stars...?

 

[ThomasEdison]

No but if a star is an energy source for life so is a gas giant with its magnetic field. Also some are hot too.

 

[mathman]

Mathman, that puzzles me. Isn't Jupiter the same age as the earth?

You are correct - I was thinking of gas giant stars. Gas giant planets are mostly hydrogen, so supporting life seems very unlikely.

 

[Matterwave]

At this point, extra-solar moons have no empirical evidence. We have no reason to suspect that our solar system is somehow unique and is the only such system with planets with moons; however, we just don't have the evidence for extra-solar moons at this point.

Another point is that since Earth is the only known planet w/ life and it is NOT a moon, this biases us to look for Earth-like planets - the other bias being that we can't even see Earth-sized objects yet (I think the smallest planet we've found is something like 6 times Earth's mass or so? A super-Earth so to speak), let along moons.

The problem with any question involving extra-terrestrial life is that we only have 1 sample point, and 1 sample point does not make a data set...