Could an Earth-like planet orbit a gas giant?

[Brandonv]

This is something I have wondered about for some time, and after watching Avatar I have been thinking about it more. For example, consider the planet 55 Cancri f (Wikipedia). It is a gas giant estimated to be about half the mass of Saturn, and spends it's entire orbit in the habitable zone of a yellow dwarf star. Let's pretend that during the formation of the 55 Cancri solar system, 55 Cancri f captures a rocky planet the size of Earth.

Some problems I can see:
-I know that Jupiter has a strong radiation field. I wonder how far away a planet would need to be to in order to be safe? Would a strong enough magnetic field protect the planet?

-I am guessing tidal forces would be quite strong, resulting in volcanic and tectonic activity.

Also, I wonder if the planet would be tidally locked, like the Earths moon? This would cause days and nights to be very long.

 

[Jetfire]

If it has moons then it is a good possiblity that one could support life. Not all gas giants are the same...Neptune & Uranus are very different than Jupiter as far as radiation and gravity...I read that floating plaforms could be placed in the upper atmosphere of Uranus and the gravity would be similar to earths...is this true?

An alternative is to place floating cities in its atmosphere, as its surface gravity is only 90% of Earth's. Saturn and Neptune could be suitable as well, but Jupiter would likely not be, due to its high gravity, escape velocity, and radiation.

 

[STR]

^Gravitational acceleration is a function of distance. So, you stick a platform around any planetary body (at the right altitude) and you'll get 1G of acceleration, or Earth gravity.

Also, given the hierarchical nature of the universe, most stars should have multiple planets, and most planets should have moons. Larger the planet, the more moons it should have. Get a large enough moon, and you get a probability of the moon having a moon of its own.

 

[STR]

Some problems I can see:
-I know that Jupiter has a strong radiation field. I wonder how far away a planet would need to be to in order to be safe? Would a strong enough magnetic field protect the planet?

Jupiter has both a strong magnetic field (which is great for blocking solar flares) and strong Van Allen belts (which will kill you if you're inside of one). However, Van Allen belts take up a finite amount of space some distance from the planet.

-I am guessing tidal forces would be quite strong, resulting in volcanic and tectonic activity.

Only if the moon is as close as Io. A little further away and the issue mitigates itself.

Also, I wonder if the planet would be tidally locked, like the Earths moon? This would cause days and nights to be very long.

The Earth's moon is tidally locked, but the whole surface does get lit. The key to the length of day in a system like this would be dictated by both the rotation of the moon, and the time it takes to revolve around its parent planet. You could vary well end up with a world with fluctuating day and night cycles.

e.g. a 12 hour day, 10 hour night, followed by a 8 hour day and 11 hour night.

Basically, there's nothing that makes a gas-giant/moon system inherently more difficult to sustain life (as far as we know) as our system of star/planet.