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the mythical "Class M" planet


g33k

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Elsethread, @Joerg made the following excellent point, that I thought deserved its own thread and discussion...

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Water worlds: Our home planet is one. This doesn‘t mean that each and every inhabitant will see the sea at least once a month.
Get over those single biome planets, folk. You can have a wet navy culture on a planet with less than 20% open water surface, and you can have huge inland areas far from any sea or lakes on a water world.
If you want to present a planet as a single biome, simply state that the planet-side spaceport is situated in so-and-so biome.

Here's the thing:  we actually have only a single data-point -- the Earth, Terra -- to know what a "normal" habitable world (what Star Trek calls a "Class M" planet) looks like.  Drake equation notwithstanding, we don't actually have DATA in-hand that there is even one other world that fits the "Class M" fiction.  Personally, I *want* it to be correct, but I'm keenly-aware of it as a VERY retrograde "armchair-science" pseudo-fact.

But even if we conclude that Drake was broadly "correct" (even if a few details were a bit off):  we have *ZERO* evidence of what sorts of worlds are "typical."

Is ours?  Or is ours a weird outlier?

The Earth is about 7/10 water, so we call it a "water world;" but what if 99% of all "Class M" planets turn out to be 99% surface-water?  Maybe Terra is nearly a desert-world...

Or maybe 2/3 to 3/4 surface-water is the norm, and to be a "water world" a planet has to be 93% surface-water...\

Etc Etc Etc...

   ***   ***   ***

How you set that "norm" for your campaign could have big implications for your universe!

 

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With Terraforming, especially Ancient Terraforming, a lot of worlds could be Earth-like, to a certain extent.

Sure, you wouldn't get hundreds of millions of years of life-geology unless the worlds were terraformed millions of years ago, but large bodies of water should be fine if you smash enough comets into the planet.

Although I agree that single biome planets don't make a lot of sense, they are easy to use.

Planets with a higher mean temperature will have more deserts, especially if they have less water.

Planets with a substantially lower temperature will be Ice Worlds, especially if they have a lot of water.

Targeted terraforming might create jungles, deserts or whatever biome you want. After all, these are engineered worlds, designed to be what you want, not natural worlds that have developed organically.

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Planetary temperature can be regulated by albedo. You could cool down Venus significantly by constructing a huge shade (and photogalvanic array) in its L1 point, leaving only the rampant volcanism as major heat source. You could filter in only the wavelengths used by the gengineered atmospheric plancton you seed the planed with to reduce carbon and sulphur oxide concentrations in the atmosphere, possibly depositing elementary sulphur in the process, to be harvested as space construction material.

A planet like Venus could be an ice ball, given the right albedo parameters, despite its greater proximity to our central fusion plant.

You can easily have cloud-shrouded hothouse planets, with dripping rainforests of whichever vegetation thrives on the radiation still getting through to the surface (if at all - it is as easily conceivable to have atmospheric plancton sending dead matter down to the ground where fungus-like sedentary vegetation will rely more on external food sources than on autotrophy).

Autotrophy doesn't have to be limited to photosynthesis. Thermosynthesis is an option even on our home planet. Organisms in an environment moving through a strong magnetic field (e.g. on Jupiter moons) might use electric induction to fuel their metabolism. You could even have autotroph organisms living on radioactive decay as the basic step of a food chain. And all that presumes that the organism is using chemical energy and not for instance electrochemistry or capacitive storage of electrical charges for its metabolism.

 

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Telling how it is excessive verbis

 

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We should also remember that a "water world" -- even if the largest land-masses are small-island-sized -- isn't a "single biome".  Tropical vs temperate vs arctic are major differences.  Tidal shallows vs. top-10-meters vs "Twilight Zone" vs dark deeps are yet more differences.  Thermal vents each have a local biome.  Etc Etc Etc.

Similarly, a "desert" world may be reasonably cool (albeit dry) in the arctic regions; or if at the outer edge of the "Goldilocks zone," perhaps the tropical/temperate belt is shirtsleeve-comfortable, but frigidly cold near the poles.

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I'd have to think about that one.  My initial instinct is, that planet would have a core of ice, due to pressure.  That's not much of an issue in game terms, though. :-)

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45 minutes ago, g33k said:

Here's an idea for a "water world" -- a great big ball of water, with *NO* solid minerals.

Just a gigameter-wide water-droplet (with an atmosphere).

 

Splendid : ) 

There's a sci-fi book with a world like that in the supporting cast. Just can't remember which one... Could it be by Iain M Banks?

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23 minutes ago, Matt_E said:

...  My initial instinct is, that planet would have a core of ice, due to pressure...

I had the same thought.  I didn't do the math, though (like you:  I don't think it matters that much for game-play).

Upon reflection, I realize that "no iron core" = "minimal magnetosphere" = strong attrition of the atmosphere.  So a star that minimized that would be good!  ;-)

 

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It depends a lot on where the planet is situated relative to it's star. To be an Earth-like (Class "M" or Minshara class), a planet has to receive about the same amount of energy per area s star that Earth does. This means that it has to be closer or further from the star depending on how much energy said star emits. That will determine how hot the planet is and if it can have liquid or frozen water or not.

The size of the planet will and its density play a big factor since it will determine the gravity, which will determine the minimum molecular weight retained.

 

Since a solid water world would be less dense than one with a rocky core, it would need to be bigger (a radius or around 15,600 km) in order to have about 1g gravity. Now since water absorbs more energy than ice, so the water world would be hotter than earth and have a lot more energetic weather. 

 

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"Now since water absorbs more energy than ice"

I don't understand this statement.  Are you referring to specific heat?  At what temperature and pressure?  I think albedo might have a bigger effect; is that what you mean?

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Another way water can exist is as a cloud of vapor in the proto-planetary disk:

 

https://www.thoughtco.com/water-in-space-4062479

 

Which would be too young for local life to evolve, however, it could be colonized. Maybe by ancient star-farers that have now senesced, yet left behind genetically adapted life-forms. Similar to Niven's Integral Trees novel, yet with water vapor replacing air in the smoke ring.  

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5 hours ago, Matt_E said:

"Now since water absorbs more energy than ice"

I don't understand this statement.  Are you referring to specific heat?  At what temperature and pressure?  I think albedo might have a bigger effect; is that what you mean?

Solar energy. Ice reflects more solar energy than liquid water. So if the water world is entirely water on the surface it will absorb more solar energy than if it had ice caps. So the planet would have a more energetic climate. So the planet could have big storms.

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4 hours ago, Atgxtg said:

Ice reflects more solar energy than liquid water.

So, albedo, then.

There will also be albedo from tremendous cloud cover that will result from the constant high humidity over most of the globe...but I'm unsure of what other than water vapor might be in the atmosphere, to trap the heat that the water is assumed to absorb...  Water or ice, if all that heat just gets re-radiated back into space, well, so much for your warm planet with energetic climate.  It's rather complicated.

However, since this is just a game, if we can accept light sabers and hyperspace travel, ahem, then I think we can overlook some of the intricacies of geophysics.

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Sulfur is ubiquitous in the universe.  There is a very specific reason why earth can support plant life instead of it all dying off in acid rains from the high sulfur content that exists here.  It's because most of the surface sulfur was blown away in asteroid and comet impacts.  The same is not true, however, of Venus and Mars, where much higher levels of sulfur exist on the surface.  The reason why this is so has profound implications on finding other planets like ours in the universe.

As Jupiter moved further away from the Sun, it pulled the asteroid belt with it.  At a certain point, the gravitational pull of Jupiter equaled that of the Sun upon the asteroid belt.  When that happened, a vibration was created.  Half the asteroid belt continued following Jupiter.  Half fell back into the sun.  During this period, the largest planet between the falling asteroids and the Sun was Earth.  It's greater gravitational field scooped up a large amount of incoming asteroids that would have hit Mars or Venus.  As a result, Earths crust took a pounding and much of the sulfur on its surface was blown into space and carried away on the solar wind.  Mars and Venus maintained there surface sulfur.  As a consequence of this, plant life was able to form on Earth and not Venus nor Mars.

Just because we find planets in the so-called "habitable zone" doesn't mean the planets will actually be habitable.  Sulfur is ubiquitous in the universe.

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8 hours ago, Matt_E said:

So, albedo, then.

There will also be albedo from tremendous cloud cover that will result from the constant high humidity over most of the globe...but I'm unsure of what other than water vapor might be in the atmosphere, to trap the heat that the water is assumed to absorb...  Water or ice, if all that heat just gets re-radiated back into space, well, so much for your warm planet with energetic climate.  It's rather complicated.

However, since this is just a game, if we can accept light sabers and hyperspace travel, ahem, then I think we can overlook some of the intricacies of geophysics.

Yes, it is rather complicated, but since it is assumed to be a Class M planet then must have an atmosphere that will help shield it and retain heat.  Its' kinda like knowing the answer to a math problem before you start work on the problem. What you end up with is already given, so  the other factors have to work out in such a way that you end up with a Class M planet. So it can only be so big (or small) and so far away from (or close to ) it's star, must have a certain amount of gravity (but not too much) etc.etc. 

 

Although, if I were going to use this planet I'd be tempted to give it a small but very dense core ( say something like depleted uranium surrounded by lead) and make the planet a little smaller. 

Chaos stalks my world, but she's a big girl and can take of herself.

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6 hours ago, Pentallion said:

Just because we find planets in the so-called "habitable zone" doesn't mean the planets will actually be habitable.  

No, but Class M planets would have to be in a habitable zone. Not necessarily a main sequence star's habitable zone, but some sort of habitable zone. Otherwise they wouldn't be Class M.

Edited by Atgxtg

Chaos stalks my world, but she's a big girl and can take of herself.

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1 hour ago, Atgxtg said:

No, but Class M planets would have to be in a habitable zone. Not necessarily a main sequence star's habitable zone, but some sort of habitable zone. Otherwise they wouldn't be Class M.

Not quite correct. While we never see this expressis verbis in Star Trek, a Class M planet could have artificial heating and lighting (or shading), if only from mirror arrays in the L1 and L2 positions. But then neither do we see space lifts, despite the fact that transporters were developed only several decades into the post contact civilisation.

Most of the "class M moons" in the series shouldn't be able to maintain an oxygen atmosphere for lack of photosynthesis, hydrology, and magnetism to protect the atmosphere.

Mars used to be Class M, judging from the surface composition (high oxygen minerals), but all oxygen was used up in the lithosphere or bonded to carbon.

Star Trek is very much science fantasy in this regard. It is almost its own genre, and definitely not Space Opera the way M-Space supports.

 

I would expect to find more planets like Komarr from the Vorkosigan saga - planets that require significant effort in order to become at least marginally habitable in the equatorial zone outside of the planetary domes.

I am a big fan of Kim Stanley Robinson's Red, Green and Blue Mars trilogy. Not necessarily the effortless immortality created on the colony, but the terraforming disputes and efforts. These ought to make for as many interesting encounters as alien biotopes.

Telling how it is excessive verbis

 

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1 hour ago, Joerg said:

Not quite correct. While we never see this expressis verbis in Star Trek, a Class M planet could have artificial heating and lighting (or shading),

Or sure, artificially produced or terraformed planets can get around all the real physics, depending on how advanced the people behind it. I've done it in Trek campaigns- sometimes retroactively when I discovered something that would have made the planet uninhabitable-after the fact. 

 

Yes, Trek is is own sub-genre. Most SF franchises are. 

One of the "drawbacks" to M-SPACE is that it ends up dictating the type of SF you use, just by setting up the the way things work. Its' not a bad thing, really. Just about every high tech RPG does it, and kinda has to. For instance Traveller uses jump drives and lacks FTL communication which causes things to work a certain way, and that way is different than the way Star Trek or Star Wars works. But is practically unavoidable for a SF RPG to do otherwise. But it does make it tougher to use M-SPACE for setting such as Trek or Star Wars. Not impossible, just tougher.

Edited by Atgxtg

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9 minutes ago, Atgxtg said:

. But it does make it tougher to use M-SPACE for setting such as Trek or Star Wars. Not impossible, just tougher.

I found M-Space to be very open ended.   One of its features seems to me to be that you can toss out anything you want and insert anything else and it still works just fine.  Star Trek and Star Wars should have no problem fitting into your own M-Space game.  If you want instantaneous sub-light communications the way Uhura seemingly does, then you just do it.

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There is also the time-scale to think of, the Earth wasn't always habitable:

More than 2.4 billion years ago, Earth's atmosphere was inhospitable, filled with toxic gases that drove wildly fluctuating surface temperatures. Understanding how today's world of mild climates and breathable air took shape is a fundamental question in Earth science.
 
Which wouldn't be habitable to us.
 
Plus with the question of age, such as comparing the Sun's 4.6 billion years to Tau Ceti's 5.8 billion, for example, there is lot that can happen in that 1.2 billion year time frame.
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53 minutes ago, Pentallion said:

I found M-Space to be very open ended.   One of its features seems to me to be that you can toss out anything you want and insert anything else and it still works just fine.  Star Trek and Star Wars should have no problem fitting into your own M-Space game.  If you want instantaneous sub-light communications the way Uhura seemingly does, then you just do it.

That's basically what you have to do, toss out what doesn't work (for a setting) and replace it with what does. But it could mean a bit of work to get everything to work out right. For Trek I'd probably do up tables for Trek styles weapons, FTL and sublight drives (sublight would probably just by SPEED/20, so A SPEED of 10 would be a sublight speed of 0.5c) and so on. 

 

Chaos stalks my world, but she's a big girl and can take of herself.

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Hey, @clarence ... might M-Space get a supplement with explicit support/discussion/exploration for universe-building with different assumptions (such as STL-only "lighthugger" physics, Bab5-wormhole vs ST-Warp style FTL, etc...)?  Instantaneous communication vs. faster-than-starship vs. jumpboat-network?

I'm interested in how the different assumptions would result in different universes, different RPG settings.  Other assumptions (where differences could lead to very-different game-worlds!) would obviously include ("obvious" because of the thread-subject)) how common "inhabitable worlds" are, how common life is in the universe, and intelligent life, and technologically-sophisticated intelligent life... 

Are the dual fates of "transcend-or-senesce" really the only ways for Ancients to exist, and for the setting to be game'able?

Etc Etc Etc...

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While I do think it would be a cool subject for a book, I don't believe I'm the person to write it. Even though I have spent most of my life reading sci-fi, it feels like I have only scratched the surface. My method these days is to skip sci-fi and read New Scientist and history books at the same time : ) 

 

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One problem with adapting M-SPACE for specific settings is the legalities involved. It's one thing if somebody posts something like an M-SPACE Phaser table or some such, but something else entirely to do an official M-SPACE STAR TREK supplement.

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