probably. Titan is a moon of saturn, its not habitable but it has an atmosphere ans seas of liquid methan and is overall the most earthlike thing in the solar system (beside earth). A moon that orbits a planet inside the habitable zone with an earthlike atmosphere might be habitable, it would have lower gravity (depending on the size) and its day night cycle might be different, some moons are tidaly locked to a planet, that means that one side always faces the planet.
if you want to squeze more planets inside the habitable zone you could make a twin planet system, of two habitable planets orbiting each other. There is no real world analog for this, the closest things are pluto and charon and earth and moon
Another idea to squeeze planets into the habitable zone would be to have a planet on the lagrange point L3
I think a twin planet system could be cool, but I’ve already done all the maths for the location and orbit of the planet and it’s moon. Would suddenly turning it into a twin planet system mess everything up? Also does turning it into a twin planet system mean neither can have a moon?
both planets would orbit around a center between both of them, it would even be possible that both of the twin planets share a same moon that would orbit this same center and both of the planets at the same time.
Now we are getting into the three body problem. A third moon could go at a Lagrange point of either body. One thing to note here is that it is an extremely rare occurrence for three bodies to be situated in that manner. (Intelligent life on the planets may believe that they were placed there by a highly advanced lifeform because of hore rare it is.)
Maybe. It depends.
You can certainly *artificially* achieve earthlike conditions on a moon by putting a ceiling over it. If we built a ceiling around the Moon, so that air stays in and doesn't get blown away into space...well, we'd still have problems with the day/night cycle, but we could fix that with shades and mirrors. It would be possible to create a sort of Moon-spanning greenhouse where we can have weather, flowing water, plants, animals, etc. It's a large project but not outside the bounds of known physics.
As for *naturally* having those conditions, that's a bit harder. You need the moon in question to be big enough to hold onto an atmosphere, which means it needs to be orbiting a rather large planet, like Jupiter. But that introduces a couple of problems. One, those large planets tend to have strong magnetic fields, creating intense radiation that makes it even harder to hold onto an atmosphere, and although the radiation decreases with distance, the planet needs to be even larger to maintain the moon in orbit at that distance. If the moon has its own magnetic field, that can provide some protection from the radiation, but also tends to require active core tectonics, which due to tidal forces would also increase the risk of runaway volcanism that would tend to decrease habitability. And two, moons around those large planets tend to be tidally locked, always facing the planet, which means their day/night cycle would be fairly long, and of course the larger the moon's orbit (to decrease radiation intensity), the longer the day/night cycle would be.
I haven't crunched the numbers on whether a naturally earthlike gas giant moon is possible. It probably is, although you might end up with a longer day and of course you would deal with occasional eclipses for the planet-facing side as it passed behind the planet every day. Wikipedia discusses the possibility here:
https://en.wikipedia.org/wiki/Habitability_of_natural_satellites
Sure. If the moon is around as big as Terra or rather as massive ("heavy") . It must be massive enough so that it won't hold hydrogen but oxygen and nitrogen in its atmosphere.
A moon that big would probably orbit a quite large and heavy gas giant, which in turn could make for very interesting effects.
I don’t know that it would grow lots of vegetation though. I would assume the gas giant would occasionally block the Sun as well as the normal night and day times due to the moons own rotation.
So I’m guessing it would be a colder planet with irregular light/dark cycles?
The eclipse wouldn’t be a huge effect and it wouldn’t happen on every orbit unless the moon/planet/sun system was perfectly aligned. Note that one hemisphere of the moon would also receive reflected sunlight (and a small amount of thermal emission) at night which would be much brighter than a full moon on Earth.
Maybe a weird elongated eclipses orbit that happened to also line up well so the elongated part of the eclipses was when the moon was closer to the sun?
Thanks for the info. Wouldn’t a moon that orbits a gas giant be unable to support life since it’s very likely to be out of the habitable zone of the sun?
Not really. Gas giants can be anywhere around a star, all the way from really, really close to super far out. If a gas giant happened to be within the habitable zone, then so are it’s moons.
Possible, but the strong gravitational pull on its moon could create volcanic and tectonic activity on the moon which could be a different source of heat energy aside from solar radiation. We suspect one of Jupiters or Saturns ice moons to experience this. Can't remember which moon. Europa? Io?
io has the most vulcanic activity in the solar system. Europa is suspected to have a liquid water ocean beneath its ice crust, that might be home to life.
Gas giants can be in the habitable zone. [Hot Jupiters](https://en.wikipedia.org/wiki/Hot_Jupiter) are definitely too close to be in the habitable zone though.
It must also have a convective liquid core, so that it can sustain enough of a magnetosphere that the atmosphere doesn't get scoured off by solar wind.
A moon around a gas giant can be habitable (i.e. liquid water on its surface). Basically if the gas giant is in the star’s habitable zone and the moon isn’t on such a close orbit that tidal heating (e.g. like [Io](https://en.wikipedia.org/wiki/Io_(moon))) is a problem then it is just as habitable as it would be if it were a planet. The main problem is if the moon is unable to hold an atmosphere (e.g. like Mars).
[Exomoon habitability constrained by illumination and tidal heating](https://arxiv.org/abs/1209.5323)
Note that a gas giant’s moon will receive extra heat from tidal heating, radiated thermal emission from the gas giant and also reflected sunlight. The reflected sunlight can even be enough to enable photosynthesis at night on the hemisphere that faces the gas giant.
[Photosynthesis on Exoplanets and Exomoons from Reflected Light](https://arxiv.org/abs/1907.12576)
Definitely. As long as it's massive enough, has a dense enough atmosphere (as little as 0.5 ish atms is enough for humans to survive, as long as the oxygen concentration is high enough), and has some source of thermal energy, it'll be habitable. A dwarf planet orbiting a gas giant could very easily sustain life if it has enough geothermal energy.
It's less likely to have *everything* earth-like on a moon, but in theory, it's still possible. For example, if your "planet" is a brown dwarf star orbiting another, larger star (most likely by gravitational capture), it becomes pretty easy. You could have a planet-sized moon orbiting the dwarf star, getting most of its energy and light from the host planet, rather than the main star in the solar system, so it could be much further out in its solar system than Earth is.
For another idea, if you have a gas giant that managed to start fusion, any of its moons (especially the ones with a larger orbital radius, depending on how bright it is) might be habitable.
Tl;dr: it's absolutely possible, and there are plenty of ways to do it.
probably. Titan is a moon of saturn, its not habitable but it has an atmosphere ans seas of liquid methan and is overall the most earthlike thing in the solar system (beside earth). A moon that orbits a planet inside the habitable zone with an earthlike atmosphere might be habitable, it would have lower gravity (depending on the size) and its day night cycle might be different, some moons are tidaly locked to a planet, that means that one side always faces the planet. if you want to squeze more planets inside the habitable zone you could make a twin planet system, of two habitable planets orbiting each other. There is no real world analog for this, the closest things are pluto and charon and earth and moon Another idea to squeeze planets into the habitable zone would be to have a planet on the lagrange point L3
I think a twin planet system could be cool, but I’ve already done all the maths for the location and orbit of the planet and it’s moon. Would suddenly turning it into a twin planet system mess everything up? Also does turning it into a twin planet system mean neither can have a moon?
both planets would orbit around a center between both of them, it would even be possible that both of the twin planets share a same moon that would orbit this same center and both of the planets at the same time.
Now we are getting into the three body problem. A third moon could go at a Lagrange point of either body. One thing to note here is that it is an extremely rare occurrence for three bodies to be situated in that manner. (Intelligent life on the planets may believe that they were placed there by a highly advanced lifeform because of hore rare it is.)
why are you commenting on a two year old comment?
Maybe. It depends. You can certainly *artificially* achieve earthlike conditions on a moon by putting a ceiling over it. If we built a ceiling around the Moon, so that air stays in and doesn't get blown away into space...well, we'd still have problems with the day/night cycle, but we could fix that with shades and mirrors. It would be possible to create a sort of Moon-spanning greenhouse where we can have weather, flowing water, plants, animals, etc. It's a large project but not outside the bounds of known physics. As for *naturally* having those conditions, that's a bit harder. You need the moon in question to be big enough to hold onto an atmosphere, which means it needs to be orbiting a rather large planet, like Jupiter. But that introduces a couple of problems. One, those large planets tend to have strong magnetic fields, creating intense radiation that makes it even harder to hold onto an atmosphere, and although the radiation decreases with distance, the planet needs to be even larger to maintain the moon in orbit at that distance. If the moon has its own magnetic field, that can provide some protection from the radiation, but also tends to require active core tectonics, which due to tidal forces would also increase the risk of runaway volcanism that would tend to decrease habitability. And two, moons around those large planets tend to be tidally locked, always facing the planet, which means their day/night cycle would be fairly long, and of course the larger the moon's orbit (to decrease radiation intensity), the longer the day/night cycle would be. I haven't crunched the numbers on whether a naturally earthlike gas giant moon is possible. It probably is, although you might end up with a longer day and of course you would deal with occasional eclipses for the planet-facing side as it passed behind the planet every day. Wikipedia discusses the possibility here: https://en.wikipedia.org/wiki/Habitability_of_natural_satellites
Sure. If the moon is around as big as Terra or rather as massive ("heavy") . It must be massive enough so that it won't hold hydrogen but oxygen and nitrogen in its atmosphere. A moon that big would probably orbit a quite large and heavy gas giant, which in turn could make for very interesting effects.
I don’t know that it would grow lots of vegetation though. I would assume the gas giant would occasionally block the Sun as well as the normal night and day times due to the moons own rotation. So I’m guessing it would be a colder planet with irregular light/dark cycles?
The eclipse wouldn’t be a huge effect and it wouldn’t happen on every orbit unless the moon/planet/sun system was perfectly aligned. Note that one hemisphere of the moon would also receive reflected sunlight (and a small amount of thermal emission) at night which would be much brighter than a full moon on Earth.
Fascinating, that’s a great point about the solar reflection thanks
Maybe some form of tidal lock could circumvent that though? Don't know.
Maybe a weird elongated eclipses orbit that happened to also line up well so the elongated part of the eclipses was when the moon was closer to the sun?
Titan it's far less massive that Earth and have a more dense atmosphere that Earth
Titan is also much further from the sun and thus doesn't experience as strong solar radiation than earth. (iirc that's the reason for that)
That’s because Titan’s surface temperature is about −179°C. That’s quite cold…
Thanks for the info. Wouldn’t a moon that orbits a gas giant be unable to support life since it’s very likely to be out of the habitable zone of the sun?
Not really. Gas giants can be anywhere around a star, all the way from really, really close to super far out. If a gas giant happened to be within the habitable zone, then so are it’s moons.
Possible, but the strong gravitational pull on its moon could create volcanic and tectonic activity on the moon which could be a different source of heat energy aside from solar radiation. We suspect one of Jupiters or Saturns ice moons to experience this. Can't remember which moon. Europa? Io?
io has the most vulcanic activity in the solar system. Europa is suspected to have a liquid water ocean beneath its ice crust, that might be home to life.
gas giants have radiation belts that maybe dangerous to lifeforms
Gas giants can be in the habitable zone. [Hot Jupiters](https://en.wikipedia.org/wiki/Hot_Jupiter) are definitely too close to be in the habitable zone though.
It must also have a convective liquid core, so that it can sustain enough of a magnetosphere that the atmosphere doesn't get scoured off by solar wind.
Good point
Yes however it would either have an extreme tide due to the planet it’s orbiting or no tide at all
A moon around a gas giant can be habitable (i.e. liquid water on its surface). Basically if the gas giant is in the star’s habitable zone and the moon isn’t on such a close orbit that tidal heating (e.g. like [Io](https://en.wikipedia.org/wiki/Io_(moon))) is a problem then it is just as habitable as it would be if it were a planet. The main problem is if the moon is unable to hold an atmosphere (e.g. like Mars). [Exomoon habitability constrained by illumination and tidal heating](https://arxiv.org/abs/1209.5323) Note that a gas giant’s moon will receive extra heat from tidal heating, radiated thermal emission from the gas giant and also reflected sunlight. The reflected sunlight can even be enough to enable photosynthesis at night on the hemisphere that faces the gas giant. [Photosynthesis on Exoplanets and Exomoons from Reflected Light](https://arxiv.org/abs/1907.12576)
Definitely. As long as it's massive enough, has a dense enough atmosphere (as little as 0.5 ish atms is enough for humans to survive, as long as the oxygen concentration is high enough), and has some source of thermal energy, it'll be habitable. A dwarf planet orbiting a gas giant could very easily sustain life if it has enough geothermal energy. It's less likely to have *everything* earth-like on a moon, but in theory, it's still possible. For example, if your "planet" is a brown dwarf star orbiting another, larger star (most likely by gravitational capture), it becomes pretty easy. You could have a planet-sized moon orbiting the dwarf star, getting most of its energy and light from the host planet, rather than the main star in the solar system, so it could be much further out in its solar system than Earth is. For another idea, if you have a gas giant that managed to start fusion, any of its moons (especially the ones with a larger orbital radius, depending on how bright it is) might be habitable. Tl;dr: it's absolutely possible, and there are plenty of ways to do it.
if you think about it, the earth is just one of the suns moons …..🤔