Life in Pioneer

[Ittiz]

Well what I'll do is create new graphics for o stars according to the regular nomenclature and let one of you guys fix the code. I currently don't have a compiler since I replaced my computer recently.

[DraQ]

Hello, my first post here, although I've been active on Frontier's official forum and, recently on SSC (Pioneer subforum).

I think the main problem with life at this point is that it appears to be assigned a fixed 0-100 degrees Celsius range - presumably meant to reflect surface liquid water, which is just plain wrong.
While the melting point of water generally stays around 0 in conditions we should concern ourselves with, the boiling point is highly dependent on temperature:


This means that below 0.006 atmospheres you don't get *any* liquid water on the surface no matter the temperature. You just go straight between solid ice and water vapour.
Even at higher pressures the range will start narrow, which isn't exactly good for chances of life - especially given that thin atmosphere won't do much good in terms of keeping temperature relatively stable and smoothing out temperature differences.

OTOH on high pressure worlds, water may stay liquid way above 100 degrees, and I'm not sure if even 250 degrees is a reasonable limit (in before heated biochemistry discussion) - sure our biopolymers (including nucleic acids) are relatively flimsy but even our usual carbon-compounds-in-water based life starting on such world might use some more stable macromolecules (or ones stabilized by for example mineral ligands), that only get labile (read: wobbly) enough for their catalytic activity at high temperatures.
As long as carbon or carbon-heteroatom backbones can stay stable we may possibly get carbon based life.

Another, completely distinct niche that has already been mentioned, is ice worlds with subsurface oceans. Basically as long as the surface is cold enough to be ice and the body gets enough tides to melt its icy interior, it may end up life bearing - you don't need much mass or any atmosphere - if it's large enough to be spherical it's good to go.

For another solvent based life (ammonia, hell maybe even methane - would an "inverted" biochemistry with molecules with hydrophilic cores floating in non-polar solvent be feasible?) you basically need to repeat the same checks as for water, except for different compound - an exception would be Europa-likes - they would still need water ice crust.
You might even have mixed solvent life, or worlds with multiple distinct biospheres, for example liquid ammonia on the surface, then water ocean under the crust.

There is also another issue that's important:
System's age. The more massive the star, the shorter it lives:

We can clearly have life around G class stars, K and M are also ok, because they live longer (they may have their potential life-bearing planets tidally locked, but we don't know *if* this is an actual problem), but even F class stars are not going to be around long enough to go beyond microbial or plant life, while A, B and O are generally not going to get even that, so if the system has such star, it won't have life-bearing planets unless they have been terraformed by humans or seeded by someone else.
Stars around Sun's mass may also last long enough in their red giant phase for life to arise around them, they may also have defrosted iceworlds (tidally heated and massive enough to harbour atmospheres even after their stars' transition) that have developed life back when they were still frozen on the surface, allowing to shorten the required lifespan somewhat (but you'll still need some billions of years total if Earth is any indication).

Lastly, temperature calculation is borked in current version. It only accounts for parent star, but multiple systems with a red/orange giant orbited by a dinky red dwarf (M class) sometimes feature enough room for a small planetary system around the red dwarf even if it's almost skimming the giant's surface, meaning comfortable room temperature or even chilly planets that have half of their sky occupied by raging inferno.

Check out Rosario's Rock, Ayphice (-14, -6, -13) for a life bearing example (IIRC) or Uraygre system (17, -19, 3) for an extreme case (but without actual life bearing worlds).

As for the atmospheres, they are currently FUBAR in many ways - quoting my post from SSC:

For starters, I don't think one should realistically expect Earth mass or larger planet to have thin or no significant atmosphere.

First of all, in our own solar system we have two earth-size planets - one is, well, Earth itself, with 1 bar atmospheric pressure, the other is Venus which has somewhere around crushing 80 bars. Ok, two planets do not a statistic make, but Pioneer's often large and massive planets with rarely even one bar of atmospheric pressure feel just wrong.
Second, universe is generally made of around 70% hydrogen, 30% helium. The rest is dominated by light elements (of which volatiles are composed). Pioneer just seems to have way too little of them.

Then we have the atmospheres. I don't think the current model listing atmospheres as if they were made of single substance cuts it. Atmospheres are typically mixes of different stuff. Earth's for example is mostly nitrogen (there goes that oxygen atmosphere...), some oxygen and various other gases, Titan, unexpectedly, is mostly nitrogen as well, despite everyone nearly instinctively associating Titan with methane (all 1.4% of it). Venus is nearly pure carbon dioxide. A lot of stuff we're thinking of as primary constituents of atmospheres are just notable additives (like our oxygen) or substances that form planet's weather cycle (whatever makes clouds and precipitation) - water here, sulfuric acid and sulfur oxides on Venus, ammonia and its salts (as well as water!) on Jupiter, same, but with methane cloud layer on top on Uranus, photopolymerized organics on Titan and so on - I think Frontier's model listing primarily weather system was much better in this regard.

Even if you decide to go with current model, it seems to assign atmospheric gasses more or less randomly, which isn't how it works at all.
What atmosphere you have is mostly determined by how massive you are and how hot.
Atmosphere, at least the one you start with, is basically what you can hold onto out of all the stuff flying around in the proplyd. You hold onto stuff using your gravity - if it's flying at more than your escape velocity, you can't have it.
How fast atoms or molecules of gas are flying is in turn determined by temperature, molecular mass and molecular structure.
Basically, AFAIK (we could really use a true physicist here) molecules of different stuff at same temperature will have same average kinetic energy (so heavier molecules are slower) and their kinetic energy will be equally split between different kind of movement (so diatomic molecules that can oscillate and rotate in addition to just flying around will be slower than single atoms of same mass, more complex ones that can rotate in more different ways and wobble around will be even slower and so on) - you can basically determine velocity distribution in gas by its molecular mass (set for any given gas), degrees of freedom per molecule (easily determined from molecular structure, also set) and temperature, then check with planet's escape velocity, although it's a bit complicated by the fact that we're speaking of a distribution of velocities, not single value, and we can allow for some gas to escape, just not too much.

Anyway, in short, hydrogen and helium are hardest to hold onto. Both are very light (meaning high velocities at given temperature), and helium, being monoatomic, doesn't spin nor oscillate (it's twice as heavy as hydrogen, though). Since they are also very abundant, I don't think we'd be dealing with any terrestrial planets with appreciable but thin (completely tenuous atmospheres may be based on different principles, like substance being released in some way and escaping) or even thick atmospheres made of those gases. If you can hold onto any hydrogen or helium, there is enough of it going around that you snowball into a gas giant - it's compunded by the fact that if you're cold (which would help reduce velocities in your gas), you'll also collect a lot of solidified volatiles (which are more abundant than rocks), which will push your mass to the point where you bloat up into a gas giant.
Oxygen is heavy and abundant enough, but awfully reactive - we wouldn't have any here if it wasn't constantly replenished by plants.
Nitrogen is a nice general purpose gas, since it's both abundant, stable and relatively heavy.
Carbon dioxide is excellent, not as stable, but much heavier - but to compound things it seems dependent on geological activity and can be tied up by stuff like liquid water and some minerals (which is why it dominates on both Venus and smallish Mars - Venus lost liquid water while Mars is just about heavy enough to hold CO2 at it's temperature).
Methane and ammonia are nice, but light-ish.
Hydrogen cyanide, carbon monoxide and hydrogen sulfide seem nice enough as well, not sure about abundance - carbon monoxide seems like it would common in atmospheres that would otherwise contain a lot of methane and water vapour, but are hot enough to make them react.
I'm not sure about ever finding appreciable amounts of argon and such.

As for oxygen rich atmospheres (note: here on Earth we still have predominately nitrogen atmosphere), I think they are more or less the result of life being water-based and having access to sunlight, so I would expect this sort of thing to develop naturally on planets with surface liquid water. In general, life will modify planet's atmosphere considerably from its primordial state.

Edit:
Regarding Ittiz's art, I've found some nice stuff:
http://ittiz.deviantart.com/gallery/
This one is not *the* most impressive visually, but check out the description:
http://ittiz.deviantart.com/art/Ammonia-World-348018019
That's the kind of stuff I'd like to see in Pioneer (or any Sci-Fi game, for that matter) please.

[FluffyFreak]

Keep it coming I like these discussions.

If something like that table can be transcribed into either another format, an equation, or done in some form of lookup table then that might be very useful.

@lwho seems to be spending a lot of time looking into the galaxy generation, which is a bit higher level than the planets themselves, but he might be familiar with some of this.

[baobobafet]

The diversity of potential life forms in the universe has now expanded beyond what many had previously thought was possible.
Check this latest report:
http://www.cbc.ca/news/technology/synth ... -1.2636341

[DraQ]

A bunch of quick questions regarding Pioneer's way of determining habitability:

1. Why are brown and white dwarfs discounted? White dwarfs seem trickiest and least likely of those, but they are capable of sustaining a small habitable zone for around 3Gy's, so if a planet forms from WD's accretion disk, it may have enough time to get to at least microbial life.

2. Conversely, why are A and B spectral classes allowed? They live too short for even microbial life to form.

3. For giant stars there should be an additional mass check - low mass red giants could live for long enough in giant stage to allow life to form and thrive in their habitable zones.

[FluffyFreak]

Bug / lack of knowledge of the subject.
Most of Pioneers contributors are just regular folk with little or no experience of astronomy, astrobiology, etc so we're just doing the best we can by reading various things.

Also you might have noticed that the code which generates the planets is quite difficult to understand. It's tricky to work out the reasoning behind a lot of the methods and calculations that it uses. Definitely lacking on comments or high level design.

[DraQ]

Ok, life possibility based on system's max possible age is done and submitted as a PR, so is life around WDs and BDs.

Liquid water and atmospheric considerations are still TBD.