We are the moon.

Some things to maybe look at for inspiration:

Europa: This moon of Jupiter is believed to be capable of sustaining life, (and in fact does - most Earth people don't realize this, but Europa is also home to JovanDisney, the largest and most elaborate of the Disney theme parks. )

Luna: Our Moon is believed by many scientists to not be a "moon", but rather, a twin planet to Earth, because never in its "orbit" of Earth does it move AWAY from Sol, the way a "true" moon would sometimes.

"Nemesis" by Issac Asimov: An excellent novel that, per Asimov's love of scientific popularization, includes an inhabited, Earth-like moon of a gas giant - and a rather thorough explantion of how such a thing could work (during a conversation between one of the astronomers and one of the leaders.)

"Spock's World" by Diane Duane: This book includes a description of the Vulcan twin-planet system - T'Charis (Vulcan) and her "moon", T'Khut. Not as thorough as Asimov, above, but still pretty sharp in scientific detail. It is also a much better picture of a Vulcan society and history than anything Paramount has seen fit to allowed to trash up our screens about them in the last decade, but that's neither here nor there.

Twin Primary systems: I can't think of a good reference at the moment, but it occurs to me that if you're not set on a moon and are just looking for an interesting planetary setup, having a world with an "orbit" that swings it around one star and then another, back and forth, like the "infinity" symbol, could be neat and have some campaign world hooks, too.

As much as having the GG always on one side of the moon would be cool, I'm going to have to decline, I'd like the world to have normal days/months that said, what other effects would having the moon out at that far have? Tide, climate and such.

I said:

What size would the planet have to be?

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I meant the GG.

I think I'm going to go with the Earth sized moon going arounda Brown Giant, on a tilted, eliptical (for fun) orbit, far enough away that it isn't tidally locked. I know it's pointless now, but a made a picture of orbits I'd like the middle one.

Thanks for all the help guys, I'm looking for some of the books Torm.

Steverooo said:

Since it must be within the life zone[snip]

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Could you explain this one? The 'Life Zone' (around Sol, at least) is the band 93 million miles around the sun, correct? One AU? Why must a planet be there to support life? It seems to me that this is a rather Terra-centric view of things. Life need not rely on the light of the sun for its energy. If life exists on Europa, it will probably subsist on chemosynthesis (the energy in the chemecals involved in deep sea hydrothermal vents caused by geological activity), more than photosynthesis (we all know this one). I could also imagine life that got its energy from the intense radiation emitted by gas giants like Jupiter. Those, however, are not environments suited to traditional DnD games, and are interesting in an off-topic sort of way. You seem to have a good understanding of these thigns, Steverooo, so if I'm wrong I'd love to be corrected.

Ferret, if you want an earth-like world revolving around a gas giant, and for it to conform to most of the accepted scientific theories about such things, it seems doable. There are issues, as I understand it, that need to be overcome before a moon like that could support human life, but they have been mentioned. A magnetic field seems necessary, but also easy to produce (Io has a very strong magnetic field, if I'm not mistaken) by the tidal forces of the orbited planet churning an iron core. The radiation produced by a Jupiter-like planet would, under ideal curcomstances, cause a beautiful aurora effect, and at worst would bake the planet to a crisp.

Very, very interesting thread. I love these things. Keep the astronomy coming.

- Kemrain the TV Astronomer.

Ferret said:

As much as having the GG always on one side of the moon would be cool, I'm going to have to decline, I'd like the world to have normal days/months that said, what other effects would having the moon out at that far have? Tide, climate and such.

Click to expand...

I will have to find some equations, and see what I can dig out...

Kemrain said:

Could you explain this one? The 'Life Zone' (around Sol, at least) is the band 93 million miles around the sun, correct? One AU? Why must a planet be there to support life? It seems to me that this is a rather Terra-centric view of things. Life need not rely on the light of the sun for its energy. If life exists on Europa, it will probably subsist on chemosynthesis (the energy in the chemecals involved in deep sea hydrothermal vents caused by geological activity), more than photosynthesis (we all know this one). I could also imagine life that got its energy from the intense radiation emitted by gas giants like Jupiter. Those, however, are not environments suited to traditional DnD games, and are interesting in an off-topic sort of way. You seem to have a good understanding of these thigns, Steverooo, so if I'm wrong I'd love to be corrected.

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In the first place, we were talking about a D&D world, with people, and all that! Anyway, the "Life Zone" of a star is the narrow band in which temperatures are right for life. In the solar system, most of the area inside 1 AU is *NOT* part of the Life Zone, as Sol's temperature is too high. Mercury & Venus cannot support liquid water (and life cannot exist without it). Outside the Life Zone, temperatures are too cold (and, again, there is no liquid water).

Sure, sure, Sci-Fi is full of monsters, and a lot of speculation is done on life on Europa, or whatever, but... show me life outside the Life Zone. Y'can't do it! And until y'can, I don't have to believe it's possible, just 'cause some NASA scientist says that it's possible (so that he can secure funding for his latest probe).

Nope, the only two places that life has ever been found are Earth/Terra (in the solar system's life zone), and Luna/Selene, our moon, also in the solar system's life zone!

What?!? You didn't know that life was found on the moon? (True story!) Then you were obviously born after the 1960... When NASA went to the moon, it was with probes, first, and both Russia and the USA landed quite a few. When Armstrong & Co. landed there, the first time, they landed within a couple of hundred yards of one of the old, non-functional probes, walked over, looked at it, disassembled one of the cameras, and brought it back to Earth...

Once here, NASA scientists in the "Clean Room" were excited to find "Moon Life" in the form of bacteria growing on the lens of the camera removed from the moon probe! Before announcements could be issued, however, it was discovered that the bacteria were terran, and had survived on the moon for over a year. So no "Moon Life", but "life on the moon" nonetheless! This is recorded in pU]The Encyclopedia of Astronomy & Space[/U], for the unbelievers.

So, it's hard enough for life to exist at the poles, or on the water-poor moon, let alone outside the life zone. The life zone of a star depends upon its size, temperature, spectral type, etc. Sol is a G2 V (IIRC). For an O, B, A, or F star, the life zone would be farther out. For spectral types K or M, it would be closer to the sun.

Also note that only Earth/Terra and Luna/Selene, our moon, are within Sol's life zone... Mercury and Venus are too close to the sun, and Mars, the asteroids, and all the outer planets are all too far away.

In general, solar systems are believed to work like this... A few planets too hot, maybe one or two with a ghost of a chance, and then a bunch too cold.

You could use magic to explain away the physics, but if you want to do that, why ask? If you want to do physics, then life is only going to exist inside the narrow band of the life zone. Save Pluto for the Fungi from Yuggoth and their undead servants and Byakhee!

I'm suprised that you seem to quick to dismiss other very plausable ideas for life-able worlds, especially given your expansive knowledge on the subject, Steverooo. To each their own. At the risk of being off topic, I'll give this reply.

When I said One AU, and 'the band 93 million miles from the sun' I hadn't meant "And everything within it," only the circular orbit at that point. Sorry for not being more clear.

I had heard about the life discovered on the moon. It's very amusing, and a very good reason not to work on probes and landers when you have a cold. I had read that the bacteria found was dormant (not reproducing or metabolizing at all) until put in petri dishes and cultured. If the bacteria found energy on the moon, I'd be suprised, but, I'd believe it.

Getting back a little on topic, Ferret, Steverooo is absolutely correct that the temparature and energy on your moon needs to be within Earth specs to support human life (without taking Magic into account, of course). I simply disagree with him that the warmpth and energy need to come directly from the sun. Putting your world within the Life Zone is the tried and true means of accomplishing this goal, as we've seen it done, once.

Steverooo, I would love to discuss such off-topic things as non-earth-like life in the Off-Topic forum, if you, or anyone else, are interested. I'm enjoying this immensely.

- Kemrain the Wannabe Stargate Physicist.

I keep seeing 93 million miles mentioned as the "Life Zone". A few observations:

1. There was life on Mars, or so most scientists now believe.

2. The range is more than just "93 million miles" - you can give or take a few million and still be within the correct range.

3. And even THEN, that number is going to vary even MORE if the star isn't Sol - the energy output level of the particular star would move the habitable range in or out.

4. And even THEN, that number will vary even MORE depending on what materials in what ratio and mass are clumped together to make up your planet - different materials will hold heat and energy differently.

5. You're talking about terrestrial style life - there could be other ways for intelligent patterns to develop than just the "pool of amino acids" bit.

6. When you're adding the variable of the "planet" in question being a moon of a larger planet that may be having its own effects on the amount and pattern of the energy the "planet" is receiving, you need all new equations, again.

Overall, I'd say fudge it entirely however you want. Your players aren't going to care that much about astrophysics, and if they do (and you're playing in an approx. 13th century culture like most campaigns) then they are METAGAMING, cause there's no way there characters should know as much about astrophysics as their 21st century players do. And if one of them IS an astrophysicist or such, recruit them to help you get all this straight.

The "life zone" is not the greatest rule of thumb I've ever run into. We only have a dozen examples of planet-sized bodies to look at, and their sizes, surface temperatures, atmospheric composition, rotational periods, magnetic fields, etc. are all over the parameter space. Liquid water exists on Earth and almost certainly under Europa's surface, so the "life zone" concept doesn't have a very good predictive success rate vis-a-vis the liquid water criterion. Planetary evolution is just way too complex to even begin to describe the preconditions for life with one scalar. That's not even getting into the inherent fallacy of the presumption that water is essential for life.

It's great to see all the discussion, I'm very curious about this kind of stuff, I don't mind if the thread is hi-jacked and moved over to Off-topic say.

Yes, the world is designed to hold Human-like life, and I will be putting it in the Life-zone, just to make it simple.

Oh when you say Sol do you mean The Sun?

Probably, since Sol is the name most astronomers use. Sun has become a sort of a noun, rather than a name, for any star around which planets orbit. Like you'd say "Tattooine twin suns" when discussing Star Wars or things like that. Sol is the first name for our sun.

I've seen the same thing used for Luna and moon.