So we’re now finding an awful of of exoplanets, most of which are gas giants. Quite a few of those are in the goldilocks zone that could allow liquid water.
So whats the implications for life on moons of gas giants in the habitable zone? Especially for it being a stable enough long term environment for intelligent life and a civilization to evolve?
Am I right that a moon needs to be pretty close to earths size in order to maintain a dense atmosphere? Could intelligent life evolve and survive in a much less dense atmosphere on a small moon? Whats the chance’s of earth size moons being around gas giants in the HZ? How bad is the radiation from gas giants for the chances of life evolving and surviving long term? Is a moon around a gas giant in the HZ likely to be more or less protected from cataclysmic asteroid or comet impacts than the earth is? What about plate tectonics / tidal forces on the moon from the gas giant?
Bonus question, how would evolving on a gas giant moon effect any civilization that did arise? I imagine that assuming the gas giant has lots of moons like ours do, that astrology and astronomy would be even more important in religion and culture.
I suspect their Copernicus would have an easier time of it. It would likely be easier to deduce and confirm (and convince the powers that be if needed) that the other moons were orbiting the planet while therefore the other planets were orbiting the sun.
Take note from Mars - it either lost or never got an atmosphere - IIRC about 1/100th Earth sea level pressure - due to size, since its gravity is 40% of earth. OTOH, maybe a moon would have a decent amount of extra atmosphere catching some of the blow-off from the mother planet.
Are they Gas giants? Well here’s an example HD10180 g is a neptune sized exoplanet smack straight in the habitable zone around a very sun like star 127 light years away.
Mars’ scarcity of atmosphere is due more to its lack of magnetic field than to its mass. Earth and Mars both have atmospheres much thinner than what would be expected, though for different reasons.
If the earth-like moon was tidally locked to the gas giant, then what happens in its oceans? It seems to me that orbiting without rotating would have the oceans acting completely differently than oceans do on Earth. Also, it would fundamentally change the nature of weather. Depending what extremes would result from these conditions, it would have to have a significant impact on culture.
Also, having a great big planet all the time in the sky would be awesome. I’m just sayin’.
Good question. Also, the day-night cycle is going to be long, any moon that was in too close orbiting fast would be deep in the radiation field of the planet. Could intelligent life evolve with a 30 day long day/night cycle? Maybe with some kind of hibernation mechanism.
There would still be tides on a tidally-locked moon of a gas giant in the habitable zone, but they would be caused by the (local) sun, not by the planet.
The length of day for such a moon would depend on how far it was from the planet, and on the mass of the planet itself. The greater the mass of the planet, the shorter the orbital period around it for any particular orbital radius. To get a reasonably short day length you need a massive planet, or a small orbital radius, or both.
Another problem could be the magnetic field of the gas giant; if it is anything like the one around Jupiter, there would be a vast flux of charged particles trapped in the field, impinging on the planet’s outer atmosphere. Perhaps the moon could have a magnetic field of its own, which might make the surface (or part of the surface) more habitable.
Tidal heating from interactions with other moons could be problematic, and might raise the temperature of a temperate moon too much (but this heating could possibly raise the temperature of a colder moon into habitability).
Some calculations show that there is a limit to the mass of a moon around a gas giant, and that an Earth-sized moon would be unlikely; but it seems entirely possible to me that such moons will occur on occasion, although they might not be all that common.
Earth, Venus and Mars are all losing their atmospheres at similar rates (somewhat greater for Mars but mainly due to its size; Venus doesn’t have a magnetic field either); the magnetic field deflects the solar wind but doesn’t deflect it completely; rather, it is funneled into the polar regions:
Also, the loss rate for Earth and Venus currently isn’t that high, equivalent to less than 4 inches of water (as oxygen ions, assuming twice as much hydrogen is lost) over 3.5 billion years; it was probably higher, possibly much higher, earlier, especially for Mars.
