In the Atmosphere

jedion357's picture
February 19, 2011 - 6:15am
Anyone aware of a table or document that tells you what sorts of chemical compositions are possible for planets in SF

It would be really good to know what mixes of gases are considered breathable

What would be breathable with some sort of oxygen concentration equipment

Whats mixes would require sealed suits- environmental or pressure suits.

Ideally a table would be the handiest

Dire Press free tools gives you atmosphere info in their system generator but it is abstract: dense toxic, thin toxic, thin reducing,  standard toxic, dense breathable

I suppose the abstract method has something to say for it- with classifications of Thin, Standard, Dense and modifiers of Reducing, Breathable, and Toxic

Yet there is no explanations as to what those terms mean in game terms; I would generally interpret toxic to require at least a gas mask or enviro suit (depends of if the gas is toxic if breathed or if its toxic if in contact with skin) Not sure what reducing means but a dense and thin atmosphere ought to have modifiers on activity.
I might not be a dralasite, vrusk or yazirian but I do play one in Star Frontiers!

jedion357's picture
February 19, 2011 - 7:07am
been doing a little web study on thin atmospheres

it would seem that the consequences of a thin atmosphere are greater temperature extremes from day to night, higher likelihood of asteroids not burning up harmlessly in the atmosphere, plus overal cooler temperatures.

The impact of a thin atmosphere, besides temperature, would be the millions of asteroids that fall, at least in Earth's case, would become a serious hazard in that environment. As for temperature- day time temps would be scalding and night time temperatures would be severely cold.

Denser atmospheres, well breathable ones, would have an impact on healing and energy of the organizisms living in those conditions. Hyperbaric chambers are used in hospitals to double atmosphere pressure to accelerate healing in certain situations- what would normally have been considered "dead" tissue has come back under double atmospheric pressure. I once heard that a tomato plant grown under such a situation had reached 25 feet in length and was at the time 5 years old. In game terms a planet with a dense atmosphere should be teaming with life, natural healing rates should be doubled, and restrictions on running and endurance should be increased, I would guess.
I might not be a dralasite, vrusk or yazirian but I do play one in Star Frontiers!

jedion357's picture
February 19, 2011 - 7:05am
Also seems that Atmospheric escape is another issue
gases escaping to space by a number of mechanisms

Themal escape is possible particularly for lighter molecules (hydrogen over CO2)

its theorized that with high pressure and temperature a "blow off" could occur where atmosphere will just flow into space.
A significant factor is the mass of a planet, high mass planets will hold onto their atmospheres better.

Solar winds and megnetic fields play a significant part but its erronous to think that no magnetic field means the atmosphere is doomed by the solar wind. Earths mag field creates a deflection of the ions in the solar wind out to 10 earth radii. Venus however lacks a powerful magnetic field and is closer to the sun but still maintains a denser atmosphere than earth.

Sequestration is loss of atmosphere through the solidification process- on earth it happened when large amounts of water became glaciers during the ice age.

A moon without a magnetic field that orbits within the bow shock of its planet's magfield will not have its atmosphere stripped by solar wind.
I might not be a dralasite, vrusk or yazirian but I do play one in Star Frontiers!

Sargonarhes's picture
February 19, 2011 - 7:45am
I beleive you'll also find that our own Earth's oxygen content to be between 15 and 25% and for good reason. If it were under 15% we'd never get any fires to burn, if it was over 25% we'd never be able to put any fires out.
In every age, in every place, the deeds of men remain the same.

Anonymous's picture
w00t (not verified)
February 19, 2011 - 1:53pm
I have the same classifications and define each one including the game effect.

TerlObar's picture
February 19, 2011 - 3:40pm
Yes, there are lots of factors that figure into the size and density of a planet's atmosphere.  As a general rule, the more massive the planet or the heavier the gasses in the atmosphere, the thicker the atmosphere will be. 

Earth's atmosphere is 78% N2 (mass = 14 amu), 21% O2 (mass = 16 amu) and 1% other stuff (CH4, CO2, CO, O3, etc.)  (amu = atomic mass unit, just a relative number for the molecular weight).

Venus, which is slightly smaller than the earth has an atmosphere that is something like 95% CO2 (mass = 28 amu) a much heavier material.  Since the molecules are heavier, they have a harder time escaping the planet's gravity and so it has a denser atmophere.  That's only part of the story, of course.  The earth has just a much CO2 but it's disolved in our oceans and locked into rock throught the process of sequestration that Jedi mentioned.

Human physiology needs a minimum of about 160 millibars partial pressure of O2 for the atmosphere to be breathable.  The total pressure of the earth's atmosphere is 1 bar (1000 millibars) at sea level.  And with 21% O2 the partial pressure is 210 millibars (roughly).  So you could do a lot of things.  If you had a pure oxygen environment at a partial pressure of 170 millibars, you could have a thin atmosphere and it would still be prefectly safe.  In fact, this is exactly what was done on the early Mercury and Gemini space missions.  It would have continued into the Apollo missions but the pure oxygen atmosphere in the command module is what caused the disasterous fire that kill the crew of Apollo 1 on the launchpad.

Or you could have a thicker atmosphere that is only a smaller fraction oxygen and it would still be fine, if a little soupy.  There is an upper limit as well (which I don't know) that beyond which, there is too much O2 and you have the uncontrolable fires issue (that is at ~25% as Sargonarhes mentioned) and problems with the body absorbing too much oxygen.

So the bare minimum atmosphere that could sustain human life would have a minimum pressure of 160 millibars and have to be pure oxygen.  Anything less and you couldn't live there without assistance.  For comparison, the entire atmosphere of Mars, which is ~95% CO2 like Venus is only 6 millibars at the surface.  (At the bottom of Valles Marinaris it is as high as 15 millibars).
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