Habitable Moons of Gas Giants?

[SpaceBadger]

I have seen many times in fiction worlds with human-habitable atmo and temperature that are actually moons of gas giants rather than independent planets.

We don't have any of these in our solar system, nor are our telescopes good enough to spot them even in other systems where we can detect planets, but their frequent occurrence suggests that they are supported by planetological theory. I don't know much of that, but am hoping that some of you more knowledgeable on the subject can answer a few questions.

Do all gas giants generate enough radiant heat to have their own orbital life zones?

How close to a gas giant would a moon have to be to benefit from this effect?

Would there be other issues to consider, as in radiation belts around the gas giant or other phenomena?

Any suggestions for rules of thumb to use in creating such worlds under the various detailed system-generation methods? (Other than GM fiat!)

 

[Fritz_Brown]

I have seen many times in fiction worlds with human-habitable atmo and temperature that are actually moons of gas giants rather than independent planets.

but their frequent occurrence suggests that they are supported by planetological theory.

Why would you think there would be any theory behind it at all?

As to Traveller: until you get into the really advanced world-making rules, there isn't any accounting for the temperature of a planet/moon. So, all those "habitable" planets around GGs in the outer orbits are... not necessarily what they claim to be. Once you run the advanced world-making (until I find some errata somewhere) you find that even most of the worlds in the habitable zone aren't a temperature that's livable.

Do all gas giants generate enough radiant heat to have their own orbital life zones?

No. However, I assume that if I get a relatively good world around a GG, and it's not too awful far out from the star, then I say, "yep, that one there is warm enough." (Yeah, I know, that sounds like GM fiat.)

How close to a gas giant would a moon have to be to benefit from this effect?

Inverse square rule. In other words, it would depend on the GG, and how close to the star it all was.

Would there be other issues to consider, as in radiation belts around the gas giant or other phenomena?

If it's close enough (and I don't know how close that would be) it might gain a benefit from any Van Allen belt around the GG. There might be radiation issues, though I don't know that we've documented any that would be problems in our own system.

Brown dwarfs are related, but sort of a different issue. Technically, the rules don't account for them, though they would provide enough heat.

If you're trying to totally randomize a sector - or even a single complete system - you aren't going to find any system that will do it accurately. There isn't enough knowledge out there. Oh, sure, someone could model stuff - if you have enough computing power (and I sure wouldn't want to see that LBB!). But why?

(If you have players that ask these questions, tell them kindly to go join Carl Sagan's gaming group, but they are welcome back if they find it a bit boring.)

 

[atpollard]

Would there be other issues to consider, as in radiation belts around the gas giant or other phenomena?

As a moon around a gas giant, I would suspect that it is probably tidally locked.
So the gas giant constantly heats one side of the moon and the other side is always freezing cold (subject to some interactions with the light from the star).

Now the entire gas giant could be in the star's liquid water zone ...

 

[SpaceBadger]

As a moon around a gas giant, I would suspect that it is probably tidally locked.
So the gas giant constantly heats one side of the moon and the other side is always freezing cold (subject to some interactions with the light from the star).

Why? Are all or most of the moons of Jupiter and Saturn tide-locked?

 

[HG_B]

We don't have any of these in our solar system, nor are our telescopes good enough to spot them even in other systems where we can detect planets, but their frequent occurrence suggests that they are supported by planetological theory.

We don't even have the tech to view Earth sized planets close by. Don't worry about it. We know almost nothing about system possibilities. Create what you want.

 

[rancke]

I understand from someone whose name I forget that Assiniboia's supposedly inhabited innermost moons would be molten from tidal stress. But moons that orbit gas giants at a decent distance should (as far as we know today) be perfectly reasonable habitations.


Hans

 

[SpaceBadger]

Why would you think there would be any theory behind it at all?

Because, as I said, it appears so often in SF, including SF written by people how usually take pains to get their world-building right.

As to Traveller: until you get into the really advanced world-making rules, there isn't any accounting for the temperature of a planet/moon. So, all those "habitable" planets around GGs in the outer orbits are... not necessarily what they claim to be. Once you run the advanced world-making (until I find some errata somewhere) you find that even most of the worlds in the habitable zone aren't a temperature that's livable.

Yeah, it is advanced system-generation that I am talking about. I wrote a program using LBB 6 rules, in BASIC on my Commodore 64 in 1985, that did a very nice job of generating sectors w all the necessary system details, then printed them out on my dot-matrix printer to be bound in folders for each sector. I'm far too lazy to re-type all that info now into a database, and the print quality isn't good enough for scanning, so I need a new program to do it all over again, and while I am at it I would like to improve the program to include the past 30 years of improvements in knowledge and theory.

Brown dwarfs are related, but sort of a different issue. Technically, the rules don't account for them, though they would provide enough heat.

Are brown dwarfs ever included in planetary systems, or only as independent solitary objects? Do we know yet if brown dwarfs ever include planet/moon systems of their own?

(If you have players that ask these questions, tell them kindly to go join Carl Sagan's gaming group, but they are welcome back if they find it a bit boring.)

I think they would find that extremely boring, since Mr. Sagan died in 1996.

The reason I want this info is primarily for me as GM. One of my initial "huh?" o: reactions when I first bought Traveller so many years ago was the notion that any system only has one "mainworld" worth talking about and the rest of the system is irrelevant. T'ain't the SF I was raised on, for sure!

My preferred method to generate a sector (non-OTU) is to randomly generate all of the systems, with star types, planets in their orbits w all usual planetary stats, moons, etc. THEN I would look at what I had and decide what to place where (main worlds, colonies, outposts, etc) based on what I found in the random stuff. THEN if I needed some stuff to be different at certain locations because of what I had in mind for this sector, I could re-roll and customize certain systems by hand.

That is all info for me, the GM, although certain amounts of it get shared to PCs through research and exploration.

 

[atpollard]

Why? Are all or most of the moons of Jupiter and Saturn tide-locked?

Most significant moons in the Solar System are tidally locked with their primaries, since they orbit very closely and tidal force increases rapidly (as a cubic) with decreasing distance. Notable exceptions are the irregular outer satellites of the gas giant planets, which orbit much farther away than the large well-known moons.

Locked to the Earth
Moon

Locked to Mars
Phobos
Deimos

Locked to Jupiter
Metis
Adrastea
Amalthea
Thebe
Io
Europa
Ganymede
Callisto

Locked to Saturn
Pan
Atlas
Prometheus
Pandora
Epimetheus
Janus
Mimas
Enceladus
Telesto
Tethys
Calypso
Dione
Rhea
Titan
Iapetus

Locked to Uranus
Miranda
Ariel
Umbriel
Titania
Oberon

Locked to Neptune
Proteus
Triton

Unless they are in a distant orbit to the Gas Giant (then they will be too cold) or have a very eccentric orbit (extreme temperature changes), they will probably be Tide-locked.

 

[HG_B]

Unless they are in a distant orbit to the Gas Giant (then they will be too cold)

If the GG is in the habitable zone the temp will be just fine. In fact, the moons of Jupiter are too cold, on the surface, for human life...

 

[whulorigan]

If the GG is in the habitable zone the temp will be just fine.

Even if the GG is in the habitable zone, remember that during each orbit of the moon around the GG there will be a period of time during which the local sun is totally eclipsed by said GG, during which time the moon will be radiating its heat away into space (unless it is significantly far away from the GG and its orbit is tilted enough out of the orbital plane). The ability of the moon's atmosphere to retain heat will affect the cooling rate, however.

 

[HG_B]

Even if the GG is in the habitable zone, remember that during each orbit of the moon around the GG there will be a period of time during which the local sun is totally eclipsed by said GG, during which time the moon will be radiating its heat away into space (unless it is significantly far away from the GG and its orbit is tilted enough out of the orbital plane). The ability of the moon's atmosphere to retain heat will affect the cooling rate, however.

Well, we've already determined that it is an outer orbit (in relation to the GG) so, just tilt the orbit a little and you're fine. It would need a significant atmosphere anyway so the short solar occlusion won't really be a problem heat wise.

 

[atpollard]

If the GG is in the habitable zone the temp will be just fine. In fact, the moons of Jupiter are too cold, on the surface, for human life...

I agree 100% ...

... but I think the opening post was thinking more along the lines of a moon being within the 'liquid water zone' of the heat radiating FROM the Gas Giant.
(of course, I could have misunderstood).

 

[HG_B]

I agree 100% ...

... but I think the opening post was thinking more along the lines of a moon being within the 'liquid water zone' of the heat radiating FROM the Gas Giant.
(of course, I could have misunderstood).

Ouch! Metis, Jupiter's closest moon is as close as you can get without the orbit quickly degrading. The surface temp on it is ~123 k (-238 Fahrenheit).

 

[whulorigan]

Ouch! Metis, Jupiter's closest moon is as close as you can get without the orbit quickly degrading. The surface temp on it is ~123 k (-238 Fahrenheit).

In fact, I am not even certain if you can get close enough to a Brown Dwarf to have a decently habitable temperature. Some Y-Type dwarfs could easily have cooled down to "room temperature".

 

[HG_B]

In fact, I am not even certain if you can get close enough to a Brown Dwarf to have a decently habitable temperature. Some Y-Type dwarfs could easily have cooled down to "room temperature".

Yes, we've detected a couple of those room temp BD's. Your starship could skim fuel from them.

 

[atpollard]

Ouch! Metis, Jupiter's closest moon is as close as you can get without the orbit quickly degrading. The surface temp on it is ~123 k (-238 Fahrenheit).

Of course the gas giant could also be closer to the sun ... like a Mars to Asteroid Belt orbit and have more solar energy to absorb and re-radiate ... and the moon could have a little more greenhouse action going on ... but we start to strain statistical probability. [Not that the Earth-Moon system is all that statistically likely.]

 

[HG_B]

So where is the line between a really large Gas Giant and a really small Brown Dwarf?
Can it give off heat without being a binary star?

Of course the gas giant could also be closer to the sun ... like a Mars to Asteroid Belt orbit and have more solar energy to absorb and re-radiate ... and the moon could have a little more greenhouse action going on ... but we start to strain statistical probability. [Not that the Earth-Moon system is all that statistically likely.]

GG's can, and are, anywhere in the system. It would be extremely easy to find (given powerful enough detection equip) LGG's in HZ orbits. Our solar system is not at all representative of what is really out there.

I don't think there will hardly be any GG's that give off enough heat on their own to support a human habitable world.

 

[pennshome723]

Look if your the GM in your own campaign, then do what ever fits for you. Heck there is no rule of thumb because honestly we just don't really know for sure what is what in space. Most of what we think we know is guess work at best...so if you want to have a Large Gas Giant in orbit 2 around some sun and there are say 4 orbits around that LGG and orbit 3 is a Earth size world and happens to have life...than just go for it!

Your in charge and your the GM and what you say is Golden...you set the rules!

 

[Fritz_Brown]

I wrote a program using LBB 6 rules, in BASIC on my Commodore 64 in 1985....

I have an Excel spreadsheet that does most of the number-crunching. (It does an entire subsector at once; and, no, I can't email it 'cause it's %$&#@%$*$ huge.) However, it's the going back to fix things that takes the most time. (It is based primarily on the advanced generation rules of LBB6, but I am adding additional info from WBH - the additional info is much easier to generate from WBH than LBB6.)

and while I am at it I would like to improve the program to include the past 30 years of improvements in knowledge and theory.

Not sure you can do that, starting with LBB6. :nonono:

I think they would find that extremely boring, since Mr. Sagan died in 1996.

(Yep. That was the point.)

My preferred method to generate a sector (non-OTU) is to randomly generate all of the systems.... THEN if I needed some stuff to be different at certain locations because of what I had in mind for this sector, I could re-roll and customize certain systems by hand.

I do go back and change the actual "dice roll" in my spreadsheet if I want to achieve something different. That way, all the restrictions stay in place. (Unless, of course, I want something that doesn't fit the rules.) It is a royal pain in the tookas, though.

I purposely went in and put in the numbers to develop a quadrary (?) system in one sector, then populated them with GGs in the habitable zones (to maximize the number of moons available), and purposely gave them captured rock planets at the inner and outer limits of the habitable zone (again, with decent-sized moons). I managed to create an isolated system with almost enough decent rocks to live on as a Firefly-style system.

Unless they are in a distant orbit to the Gas Giant (then they will be too cold) or have a very eccentric orbit (extreme temperature changes), they will probably be Tide-locked.

This might be true in RL, but the generation systems make it very possible to have a non-locked moon around a GG.

If the GG is in the habitable zone the temp will be just fine.

Not necessarily, according to the rules (which I freely admit might be broke - or my calculations might be wrong :toast: ).

 

[HG_B]

Not necessarily, according to the rules (which I freely admit might be broke - or my calculations might be wrong :toast: ).

I haven't studied those rules yet. But if they give major problems to temps being okay when a world is in the HZ (all else being equal with planetary atmos., etc.) then bizarre would be a better term than 'broken'...