Habitable Moons of Gas Giants?

[SpaceBadger]

... 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.

Yep, that's the idea.

I found my copy of Stephen Gillett's "World-Building: A writer's guide to constructing star systems and life-supporting worlds" (Baen, 1995). Instead of radiant heat from the GG, he discusses the possibility of heat in the form of tidal flexing, giving Io and Europa as examples in our system. He also has a section on brown dwarfs, which may give off sufficient radiant heat to make a moon habitable, depending on where the BD is in its lifespan.

I've also been reading more online about GGs in the inner part of a star system, the Hot Jupiters/Saturns/Neptunes.

I'm beginning to feel a bit like Jon Snow, at least in the way of knowing nothing.

Perhaps the most "realistic" idea is to just randomly allow any kind of planet in any orbit, but that just doesn't feel right. :nonono:

 

[Vladika]

... 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..

Wow! That 's a blast from the past. I used LLB 1-3 and did the same on a TI-99 4A in '81 or '82? While still in undergraduate school anyway and I graduated in '83. Upgraded it later from LLB 6, but the formuli errata was extreme in Scouts!

That thing had just 16K memory on-board and only upgradeable to 64K TOTAL. Data storage was on casset tapes... You learned to write some very efficient programs.

No wonder everyone thought computers were always going to be huge!

 

[BlackBat242]

Wow! That 's a blast from the past. I used LLB 1-3 and did the same on a TI-99 4A in '81 or '82? While still in undergraduate school anyway and I graduated in '83. Upgraded it later from LLB 6, but the formuli errata was extreme in Scouts!

That thing had just 16K memory on-board and only upgradeable to 64K TOTAL. Data storage was on casset tapes... You learned to write some very efficient programs.

No wonder everyone thought computers were always going to be huge!

You learned to write some very elegant programs.

Fixed that for you.

http://programmers.stackexchange.com/questions/97912/how-do-you-define-elegant-code

 

[Fritz_Brown]

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'...

I will tend to agree. I've gotten temps of -50C in the habitable zone, for an Earth-like planet. Mind you, that's the average, before applying axial tilt and eccentricity and other effects - solely the product of illumination, atmosphere, and hydrosphere. (And +76C for a similar hunk of rock in a different system.)

[x678###-#, F4 V, orbit 5 -> -51
x574###-#, F0 IV, orbit 6 -> +76]

(Looking at my numbers, most of the extremes are not regular worlds: belts - which shouldn't even really be doing the calculation - and airless moons and such. Looking at another one, I might have an error in my spreadsheet, as the star info doesn't look right after applying the variability.)

 

[rancke]

I will tend to agree. I've gotten temps of -50C in the habitable zone, for an Earth-like planet. Mind you, that's the average, before applying axial tilt and eccentricity and other effects - solely the product of illumination, atmosphere, and hydrosphere. (And +76C for a similar hunk of rock in a different system.)

I don't have a problem with that. A world doesn't have a comfortable temperature guaranteed just because it's in the habitable zone. And you can usually fiddle with the factors and/or move it to someplace in the habitable zone where it does have comfortable temperatures.


Hans

 

[Fritz_Brown]

A world doesn't have a comfortable temperature guaranteed just because it's in the habitable zone.

Yes, but -50 and +76 for an "M-type" planet seems a bit extreme. When you get airless moons and such, it can get even more extreme.

And you can usually fiddle with the factors and/or move it to someplace in the habitable zone where it does have comfortable temperatures.

First, the formula uses whole numbers only for its orbits when giving you an orbital factor. Second, if I have to fiddle with the factors, then I defeat the purpose of a formula. And, it will take a lot longer. (I still have to do another 15 subsectors.)

 

[rancke]

First, the formula uses whole numbers only for its orbits when giving you an orbital factor. Second, if I have to fiddle with the factors, then I defeat the purpose of a formula. And, it will take a lot longer. (I still have to do another 15 subsectors.)

Correct, detailed, quick: Pick two.


Hans

 

[HG_B]

I will tend to agree. I've gotten temps of -50C in the habitable zone, for an Earth-like planet. Mind you, that's the average, before applying axial tilt and eccentricity and other effects - solely the product of illumination, atmosphere, and hydrosphere. (And +76C for a similar hunk of rock in a different system.)

[x678###-#, F4 V, orbit 5 -> -51
x574###-#, F0 IV, orbit 6 -> +76]

(Looking at my numbers, most of the extremes are not regular worlds: belts - which shouldn't even really be doing the calculation - and airless moons and such. Looking at another one, I might have an error in my spreadsheet, as the star info doesn't look right after applying the variability.)

With good atmosphere and decent axial tilt you should end up with temp from glaciated to torrid but, capable of supporting human life even if harsh conditions. From your examples sounds like it needs a rewrite to make it work.

 

[Ishmael]

Again, be aware that the equation in book 6 for world averaged temperature is incorrect and that the error most likely propogated through World Builder's Handbook and even World Tamer's Handbook as well.

I've already posted about this issue in the past complete with corrections, etc. in my alternate UWP procedure.

 

[rancke]

Again, be aware that the equation in book 6 for world averaged temperature is incorrect and that the error most likely propogated through World Builder's Handbook and even World Tamer's Handbook as well.

I've already posted about this issue in the past complete with corrections, etc. in my alternate UWP procedure.

I use a combination of WBH and GT:First In when doing full treatments of star systems. Orbital distances and their influence on blackbody temperature of mainworlds I get from FI.


Hans

 

[lspitz]

I've been through the literature. Current real-world science does support the idea of habitable moons of gas giant planets. It gets complicated, but you can pluck out some rules of thumb:

- such satellites will almost certainly be tidally locked to their primary, barring some pretty exotic exceptions. Not a problem for habitability if the orbital period of the satellite is on the order of a few days.

- the scenarios being explored by scientists are those where the gas giant itself is in the habitable zone; the moon gets its heat from the star, not its parent planet. Brown dwarfs just don't stay hot enough long enough to maintain much of an ecosphere around them.

- the gas giant must be pretty big in order for moons of sufficient size to form around it. They need to be big enough to hold onto an atmosphere if you're aiming for complex life and human habitability. Computer simulations strongly suggest that satellites of gas giants formed in situ can't exceed 1/10000 the mass of the parent gas giant, so Jupiter-sized planets aren't going to cut it. Realistically, we're talking the 15-Jupiter-mass range and up.

- tidal heating may help drive geological processes on smaller world that would normally not have enough internal heat generated radioactively to maintain a carbonate-silicate cycle. It can be too much of a good thing, though, and I've seen at least one paper that explores the concept of the "tidal habitable zone", with respect to both a parent gas giant and a small red dwarf star. Sometimes the "insolation habitable zone" and the "tidal habitable zone" do not coincide.

So current science thinks they're possible, with certain caveats.

 

[pennshome723]

:file_21:

I've been through the literature. Current real-world science does support the idea of habitable moons of gas giant planets. It gets complicated, but you can pluck out some rules of thumb:

- such satellites will almost certainly be tidally locked to their primary, barring some pretty exotic exceptions. Not a problem for habitability if the orbital period of the satellite is on the order of a few days.

- the scenarios being explored by scientists are those where the gas giant itself is in the habitable zone; the moon gets its heat from the star, not its parent planet. Brown dwarfs just don't stay hot enough long enough to maintain much of an ecosphere around them.

- the gas giant must be pretty big in order for moons of sufficient size to form around it. They need to be big enough to hold onto an atmosphere if you're aiming for complex life and human habitability. Computer simulations strongly suggest that satellites of gas giants formed in situ can't exceed 1/10000 the mass of the parent gas giant, so Jupiter-sized planets aren't going to cut it. Realistically, we're talking the 15-Jupiter-mass range and up.

- tidal heating may help drive geological processes on smaller world that would normally not have enough internal heat generated radioactively to maintain a carbonate-silicate cycle. It can be too much of a good thing, though, and I've seen at least one paper that explores the concept of the "tidal habitable zone", with respect to both a parent gas giant and a small red dwarf star. Sometimes the "insolation habitable zone" and the "tidal habitable zone" do not coincide.

So current science thinks they're possible, with certain caveats.

Hmmm I have been playing this game for a long time and it always amazes me how people forget that Traveller is a Science Fiction game and not Papers and Paycheck real life. Now I do thank the above player for the current best guess by science, but in the end we play these games to have fun and not exist in the true real world. So if a GM wishes to do his own thing, by all means DO IT! To HECK with an written guideline, they are just that...GUIDELINES and NOT to be LAW! If you want to make a world as a moon about a LGG, they go ahead and do it. Your the GM what you say is LAW in the game. No one knows for sure and all our best scientists really are just guessing from what limited knowledge they currently have at hand. No one knows any of this for sure and anyone that says they do is just fooling themselves and shoveling you know what!

Now I am not trying to be mean here and if someone wants to try and use the current best guess of what is hard science, then to each his own. I too like Sudo Realism, but in the end having fun and playability are the real purpose for the game. So to each his own, I will get off my Soap Box now and DUCK for cover...LMAO<VBG>!!!

 

[whulorigan]

Realistically, we're talking the 15-Jupiter-mass range and up.

BTW, according to the best guess of current science, a 15 Jupiter-Mass range GG puts it into the Brown Dwarf category (13 Jupiter Masses is the current estimated lower limit, I believe).

 

[lspitz]

BTW, according to the best guess of current science, a 15 Jupiter-Mass range GG puts it into the Brown Dwarf category (13 Jupiter Masses is the current estimated lower limit, I believe).

This is absolutely true, but not especially relevant to the habitability of a moon. Early in the system's history, the brown dwarf will briefly be a significant source of heat for the moon (potentially even making things too hot for life to get a start right away and delaying abiogenesis). After a billion years (give or take a few hundred million, depending on its mass), the deuterium runs out and the brown dwarf cools significantly. The moon will ultimately be dependent on the star for its energy, at least on the timescales relevant to complex life. A brown dwarf can't be relied on as the source of heat/light to run a terrestrial-type biosphere in the long term.

I think the world needs a good, compact word for "brown dwarf that is no longer fusing deuterium".

 

[lspitz]

:file_21:


Hmmm I have been playing this game for a long time and it always amazes me how people forget that Traveller is a Science Fiction game and not Papers and Paycheck real life. Now I do thank the above player for the current best guess by science, but in the end we play these games to have fun and not exist in the true real world. So if a GM wishes to do his own thing, by all means DO IT! To HECK with an written guideline, they are just that...GUIDELINES and NOT to be LAW! If you want to make a world as a moon about a LGG, they go ahead and do it. Your the GM what you say is LAW in the game. No one knows for sure and all our best scientists really are just guessing from what limited knowledge they currently have at hand. No one knows any of this for sure and anyone that says they do is just fooling themselves and shoveling you know what!

Now I am not trying to be mean here and if someone wants to try and use the current best guess of what is hard science, then to each his own. I too like Sudo Realism, but in the end having fun and playability are the real purpose for the game. So to each his own, I will get off my Soap Box now and DUCK for cover...LMAO<VBG>!!!

I was directly addressing SpaceBadger's original question, which was "Any suggestions for rules of thumb to use in creating such worlds under the various detailed system-generation methods? (Other than GM fiat!)".

I agree, you should do what you want in your game. If it's not fun for you, what's the point?

 

[pennshome723]

I meant no disrespect to anyone, but to many times some players get so hung up on the rules that they forget the Fun Factor of it all.

I salute you with your Science knowledge though sir!!!

 

[lspitz]

I meant no disrespect to anyone, but to many times some players get so hung up on the rules that they forget the Fun Factor of it all.

I salute you with your Science knowledge though sir!!!

I feel a compulsion to look stuff up when I'm curious. It's a hazard of being a real-world scientist.

Happy gaming!

 

[whulorigan]

This is absolutely true, but not especially relevant to the habitability of a moon.

I agree. My point in bringing it up is that Traveller usually makes a distinction in its World Builders between GG's and Brown Dwarfs. If our practical lower limit for GGs/BDs with habitable world-moons is 15 Jupiter Masses, then all habitable moons (like Regina, if I recall), should be explicitly noted or generated as orbiting Brown Dwarfs, not GG's. And that is fine, but the World Builder system should make that explicit (for those interested in the scientific side of the game, at any rate).

I think the world needs a good, compact word for "brown dwarf that is no longer fusing deuterium".

I agree. I have thought that for some time. And "Post-Brown Dwarf" doesn't work for me.

 

[Limburger59]

I meant no disrespect to anyone, but to many times some players get so hung up on the rules that they forget the Fun Factor of it all.

I salute you with your Science knowledge though sir!!!

I vote for the Fun Factor and GM fiat.

The first mention of a GG moon being inhabitable that I recall was Heinlein's Farmer in the Sky written in the early 50's for teens. Even then the terraforming of Ganymede required a heat shield of some sort to hold in the heat. That book had a Fun Factor when I was young.

Honestly, without the enjoyment of role playing and tweaked systems, 99.9% of the planets in any Traveller universe would be unihabitable, and the percentage of moons would be worse.

 

[atpollard]

I agree. I have thought that for some time. And "Post-Brown Dwarf" doesn't work for me.

An old brown dwarf is a "Brown Duffer".