Planet temperature...

The temperature formula is completely based upon the distance of the planet from the center of the solar system and the number of suns in the system, with planets closer to the sun being hot, and far away being frozen rocks. It doesn't take into account the internal heat that a planet naturally generates via gravitic forces or the effects of a greenhouse environment. If you take a look at the formula you'd see that it's just straight "guess-imation". Of course, as far as I can tell, it has absolutely no effect on gameplay... so aside from being visibly odd, it doesn't do any real harm.

As for the difference between Ice and Rock planets, there is very little with the exception of the abundance of water. An Ice planet IMO is one composed mainly of liquid, a rock is one mainly of solid materials, and a gas giant is well... full of gasses (of course, that's just my take on it). Temperature wise, you will find plenty of extremely hot ice planets and freezing gas giants due to the way the galaxy is generated.

Perhaps someday in the future we'll get a mod that make "sense" of these various statistics, but right now, it's best to just ignore them.

There was a (mini) mod out there that rationalized the values given so no more ice-worlds above boiling and the like. Not sure where it ran off to.

There are 10 types of people in the world:

Those that understand binary, and those that don't.

I think there was a file called "formulas.txt" or something like that.

There are 10 types of people in the world:

Those that understand binary, and those that don't.

Logically with the stock version formula a lot of planets should be airless because most of the gas in the atmosphere would freeze solid :
Carbon-dioxide turns to solid at –78°C, Methane at -162 °C and Oxygen at -183°C.
For example if a planet temperature is below –78°C it cannot have a carbon-dioxide atmosphere, except maybe in some specific volcanic areas.

I think a feature request is in order here. I would like the ability in formulas.txt to specify a different formula for each planet/atmosphere type. Purely a flavor request, but I think it would be nice.

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Shazbot!

I'm pretty sure you can do that already, though I haven't tested it. The various planet files specify which formula they refer to.

I believe that this "illogic" with the temperatures exist because the game has to be balanced.

I remember that in SE4 until late the best home planet was the "Hydrogen Gas Giant", because that way you had lots of huge planets to colonize, while Rock and Ice planets were much smaller. With the last version choosing the home planets was just a matter of "taste", and the game was much more balanced.

Now you can have "Tiny Gas Giants"; it seems illogic, but it is good becase there is no "better choice". It is the same with temperatures.

Tempature, gravity, and radiation aren't used in-game; they're for flavor only. No balance issues.

I thought that someone was thinking to create a mod to actually use those values, and I was explaining why those values weren't used...

Maybe I didn't explain myself :|

Unfortunately with the current setup, there's no way to really use them in game. Back in the early days I had suggested a system where a race that closely matched the planet's stats might gain some extra space on the planet and vice versa.

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Space Empires Depot | SE:V Balance Mod

The Balance Mod does feature improved planet placement as ice planets will be further out from stars - but I haven't completely revised the formulas yet so that it never produces ice planets above 0°C. But at least they don't exceed -273°C anymore.

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Space Empires Depot | SE:V Balance Mod

I agree, for example most rock or ice planets should rarely have hydrogen atmosphere (or at least hydrogen should not be the main component of their atmosphere) : hydrogen is a very light gas and rock and ice planets gravity fields are to weak to prevent hydrogen from escaping into space shortly after the formation of these planets. Most of hydrogen atmosphere planets should be gas giants.

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Feel lucky earthling ?

I think there is a way to modify the system txt files to restrict placement of the Ice and Gas planets. You would have to edit the standard system descriptors.