This might be a weird question. I am creating a mini-setting for my current game. It is set on a moon of a gas giant, roughly Earth size and gravity.
How would life be like on a planet/moon like this? I assume tides would be weird and large part of the year it would have the local sun eclipsed by the gas giant. What else is there I should include?
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Have a look at the Traveller thread Anon, should answer all your SciFi howtos
I'll post it there then, thanks.
glhf with traveller zoom zoom!
The moon is guaranteed to be tidally locked, with a local sol lasting days to months depending on the mass of the primary and the moon's orbital altitude. Add to this regular eclipses lasting for hours (less time and less likely per orbit if it's more distant) and adaptation to long and sometimes irregular days are a must - if the orbit is inclined a bit and the moon has some distance, there would be two predictable eclipse seasons per year ("year" being the primary's orbit). Tides go in and out once per orbit, dictated by orbital eccentricity rather than other satellites and may be large or small depending on the magnitude of the eccentricity and orbital altitude. Any local seasons will depend on whether its orbit is inclined (the difference in inclination of the orbit relative to the primary's orbit will serve as its axial tilt) and the orbital eccentricity of the primary (solar apoapsis = winter, solar periapsis = summer). Very long days, a weak Coriolis effect and muted seasons produces simple climatology and little variation in weather for a given place.
Giant planet orbits are generally a rather hostile place for life. A Jovian may host a powerful magnetosphere and radiation belts, necessitating the planet to be placed outside of these belts and hosting a beefy magnetosphere with spectacular aurorae to defend itself and not have its atmosphere stripped away (and may pose a formidable barrier to manned space travel without shielding). Furthermore, the huge gravity well of the primary draws in all sorts of junk and its vicinity is like a planetary shooting gallery with asteroids and comets flying every which way at high speed (see: Shoemaker-Levy 9). Frequent impact events are a fact of life for the world that is extremely likely to have suffered many extinction-level events in the past that may even have thrown it back to the microbial level and the evolution of any complex life will have been ten steps forward, nine steps back.
Thx m8
That is actually pretty cool. Do you have a blog or smth like this? I'd like to read stuff you (might) write.
While I can answer questions, I tend to flounder when it comes to "go and write about a topic". A lot of what I know is from scientific rabbit holes, collected trivia and an Earth science degree so I'd certainly defer to someone who has a real background in the subject.
Exactly why Titan has a thick atmosphere is not well understood and is still the subject of scientific back and forth. It has no magnetosphere of its own but has strong gravity for a moon that helps it hold on to gas and orbits on the fringe of Saturn's magnetosphere outside the radiation belts and more intense parts and is losing atmosphere, just at a low rate. However, early in its history, the Sun was much more energetic and Titan was outside the Saturnian magnetosphere, exposing it to intense early solar wind that did blast away a lot of its atmosphere, it just had a lot to lose - what we have now is the remains. The inner Saturnian and the Jovian moons are not so lucky and get stripped of anything they put out.
Magnetospheres very much do strip away atmospheres wholesale. High-energy particles caught in the field ionise gas in the upper atmosphere which - now being charged - gets grabbed by the magnetosphere and swept away. High gravity helps the planet recapture errant gas and the heavier the gas and stronger the gravity, the higher the incoming particle energy and stronger the magnetosphere needs to be to yoink it, but having a local magnetosphere fends off the incoming charged particles and foreign magnetosphere to stop the gas going flying in the first place. Either high gravity or a magnetosphere will do the job - Earth has both, Venus has gravity (and a small induced magnetosphere), Mars has neither and Titan has some gravity and a nice neighborhood.
>Magnetospheres very much do strip away atmospheres wholesale.
no they don't, i even gave you examples of atmospheres that are still there without a magnetosphere protecting them
>Either high gravity or a magnetosphere will do the job
wait are you just repeating what i said to be an butthole?
anyway ignorning that you should probably also mention the composition of the atmosphere gets drastically changed because light elements like hydrogen are strongly preferred for solar wind stripping, which is why mars' hydrosphere mostly got stripped of its hydrogen while its oxygen proceeded to oxidize the landscape instead of flying away
How does Titan keep its atmosphere? Does it have a strong magnetosphere?
gravity is what primarily keeps an atmosphere stable over geologic timeframes, not magnetism, though magnetism helps keep its composition stable
in the case of mars, the magnetosphere failing probably caused the depletion of its oceans over the eons, however it couldn't have had a very thick atmosphere to begin with
venus doesn't have a prominent magnetosphere either and yet it has a very thick atmosphere by gravity alone, and it manages that even closer to the sun than earth
in the case of titan its distance from the sun certainly helps, but it also started out with a very thick atmosphere
it's possible that earth also started with a much thicker atmosphere than it has today, but the reason it thinned out to modern levels is mostly related to tectonics instead of loss to outer space, since earth has the tectonic activity to keep recycling gasses back underground; since the majority of water is actually impregnated in deep minerals as opposed to on the surface, it's possible that this has also helped maintain earth's hydrosphere
>gravity is what primarily keeps an atmosphere stable over geologic timeframes
Obviously wrong, because Titan.
titan is an example of why that's right anon
incidentally the heavy water impregnation of earth's crust and mantle is the reason why i think the speculations about some moons in the solar system having underground oceans is a meme, because earth would exhibit the exact same thing even if it didn't have surface water, but we know that the water in tectonic depths on earth is not liquid, it's dissolved into rocks and there's a lot of it
That doesn't track because Earth is a wholly metal-silicate body, the water content is just a very minor accessory in the scheme of things and is distributed in low concentrations through the upper mantle. The icy moons on the other hand contain a whole lot of ice with the whole outer part of the planet made entirely of ice with plenty of places for pockets of water.
Calm down friendo, I somehow slightly but fundamentally misread the point you were making and crossed some mental wires - I didn't say a magnetosphere is a requirement for a planet to avoid losing its atmosphere (though it certainly helps), I said they are capable of stripping the atmospheres of moons entirely, just preferentially removing light elements and rambled about both in self-inflicted confusion. You are right on all counts, I was arguing the wrong point entirely.
The early atmosphere may have been mostly steam, which condensed out rapidly and carbon dioxide later got gradually scrubbed by carbonate rock formation and silicate weathering. The relationship between tectonics and water is sorta the other way around, since plate tectonic processes on Earth rely on water to function and water has been gradually lost to the mantle, with more going down in subducting slabs than comes back up.
>Earth is a wholly metal-silicate body
it doesn't change the fact that earth would exhibit the same evidence of a subsurface ocean while we know it doesn't have one
>water has been gradually lost to the mantle
that's interesting, i've never heard of it and it seems counterintuitive given that earth has gone through billions of years of subduction in the past already, is there evidence that the surface had significantly more water in the distant past?
Earth still has lakes buried under miles of ice sheet that don't suddenly dissolve into the rock. And if you want to bring in Earth specifically, it does have molten silicate buried within the solid silicate, so there's no reason an icy body can't have molten ice buried within or under the solid ice, whether or not it's an "ocean" or just pockets of water. The rocky part of the icy moons is also cold and thoroughly solidified with water having no route in or means to dissolve in it.
The dewatering processes in subduction isn't well understood and there's dispute over how much goes down and how much comes back up. It's known that water still remains trapped within serpentinites and lower crust in the lithospheric mantle and gets dragged down along with it, but nobody knows how much for sure. As the crust has evolved and slowed down, more water gets lost - fresh and hot subduction zones are very efficient at recycling water but the ones eating thick, old oceanic crust have high loss rates, taking perhaps a third or more down into the depths with them.
Precambrian records of sea level are sparse but the volume of the continents has increased significantly through the Phanerozoic while the continental freeboard has not significantly changed on average, with what would otherwise be a large sea level rise failing to materialise as water loss has kept pace. Indeed, in the Archaean, sea levels were at some points high enough to submerge most of the landmasses, and that was with the oceans taking up much more volume than today.
Incidentally, this is how much of the mantle water you talk about got down there - since the mantle spat out the vast majority of its water during the formation of Earth, this is how it goes home and stays there.
You would have religions and beliefs forming around the strange patterns of their giant gaseous neighbour, similar to how religions and beliefs were started from the sun, moon and stars.
Ignorance is magic.
>How would life be like on a planet/moon like this?
look into Kenshi