Extreme Planetary Features vs realism

[xpian]

Moon of a Large Gas Giant
I think most physicists believe this to be entirely possible. A gas giant can get very large before it ignites to form a star. Some estimates are that it would take TEN Jupiter masses before nuclear fusion could ignite. So Jupiter is already huge, but you can get a lot bigger and still be a gas giant planet. A big gas giant can have very large moons: Ganymede is larger than Mercury or Pluto. Something the size of Mars or Earth could easily orbit a large gas giant.

As for radiation, the inhabitants of such a moon would be even better off than they are on Earth. Jupiter has a massive magnetic field that deflects a great deal of solar and interstellar radiation. And an earth-size moon could easily have its own strong magnetic field adding to that protection. Even Ganymede has its own magnetosphere.

As for warmth, it's true that Jupiter is quite a ways out in the solar system, and thus gets a tiny fraction of the solar radiation the Earth does. This means that Ganymede, Callisto, and Europa are all frozen solid on the surface. But we now know that jupiter-like gas giants don't need to be far from their star. Our planetary surveys have shown many "hot jupiters" orbiting nearby stars at many distances, from the baking zone of Mercury and Venus out to the goldilocks zone (liquid water) of Earth. It's entirely possible to have an inhabited gas giant moon at a comfortable range. Plus, the gas giant itself is likely radiating some heat. Jupiter does this: it puts out more heat into the universe than its taking in. We're not entirely sure why...we know it's not fusion going on, but must be some other process deep within the planet.

And while its true that Io is super hot due to jupiter's tidal forces heating it up, that wouldn't necessarily happen to any inhabited moon. It's all a function of the orbital distance.

Atmosphere is no problem for such a moon. Titan, for instance, has a very thick atmosphere with wind, rain, etc.

[BlackChakram]

I can contribute some details here as well.

Moon of a Larger Gas Giant
While gas giants do have huge magnetic fields that deflect a lot of radiation, they also create tons. Jupiter's moon, Io for example is in a radiation belt strong enough to give a human a lethal dose in a very short timespan. I can elaborate on xpian's ideas about heat generation as well. Jupiter generates heat because it's still contracting from its formation. That gravitational energy is radiated out slowly. However, this energy does little to warm anything except Jupiter itself.

Additionally, unless your moon is a captured asteroid, it's almost guaranteed to be composed primarily of ice. Most of the gas giant moons are. This has advantages, though. The tidal forces that stretch Io are also suspected to be stretching Europa and Callisto, possibly creating a liquid ocean beneath a surface of ice. Sooo, if you want an aquatic race, gas giant moons are excellent. But xpian is right. You could easily have something like an earth-sized planet an acceptable distance from a gas giant to support life. With a thick enough atmosphere, you could even keep it relatively warm.

Twin Earths
Entirely possible. In fact, Earth and its moon are considered to be a "double planet" because they're so close in size (astronomically speaking). This likely would cause tidal locking, but wouldn't necessarily mean some parts of each planet get no sunlight. The moon is tidally locked to earth, but because its axis is tilted, it doesn't create an eclipse every time it orbits.

Axial Tilting Periodical Movements
Yes. Theoretically possible. What you're describing is an effect called "precession". Earth does it at a small angle on a 50,000 year cycle. Think of it like a spinning top that starts to wobble. We don't see this mess with the seasons on Earth because that 50,000 year period is far slower than the 365 day period for a year. But IF you had a planet that was precessing much faster than it was orbiting, you could get some wonky effects. However, any planet precessing that fast would sort of even itself out. So the only way you could do this would be to bend reality and have the planet precess very quickly but have a very far orbit. Science fiction, right!

I can add a few other crazy ideas, too.

Interesting Exosolar Planets
Some of the planets we're theorizing have some crazy properties. Planets tidally locked with their parent stars so that one side is permanently dark, the other bright. This creates turbulent wind patterns at the terminator (the border between light and dark). You could then have a planet with permanent areas of twilight with permanent violent storms.

We've also theorized that there are "carbon planets" composed almost entirely of carbon. These planets could literally have volcanoes that erupt diamonds.

Rogue Planets
It's hardly impossible to have planets that get flung away from their parent stars and sent into deep space. These rogue planets would literally just wander between stars, almost permanently dark and frozen. But you could have life living deep under the surface, surviving on heat radiating from the core. I think there was a Star Trek Voyager episode that did something with a rogue planet.


If your axial tilt is stuck vertically (which, if I understand what you're getting at would mean NO tilt), then you pretty much won't have seasons. You'll get a planet with weather the same all year round. Farther north you go, the colder it gets, but that'd be about it. If your trajectory is elliptical enough, you will get seasons, but they'll affect the entire planet at once, rather than the north-south hemisphere opposites we get on earth.

[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]

There is a possible way a planet can host earthly life in the cold zone of a star system..... A gas giants moon if close enough to its parent planet can give off geothermal heat in the atmosphere via volcanic activity but the thing is it has to contain ice in the first place for it to work. not all life depends on sunlight to live deep oceans geothermal vents proved that. just imagin humanoids that use nocturnal vision to see walking in a dark Chemosynthetic forest. the area filled with hydrothermal oceans and geothermal hot spots. the normally toxic chemicals wouldnt be a problem because of the chemosynthesis the strange plants use. it would be very very dark like an eternal night so humans would need nightvision goggles. But it is indeed possible that such a place exists.

[Trollface13]

Thanks for the correction.... i need to update my knolege.... turns out my info was incorrect i thought the moon was vital to earths survival but i guess i was informed wrong.

[Trollface13]

however i do have a question..... can a city planet like coruscant even exist? or would you need to keep some natural environment in a few places so the place doesnt kill itself?