Help from knowledgeable ENworlders about biology/chemistry/astronomy

Turanil · Jul 15, 2006

So, in the prospect of joining a sci-fi game, I have to describe a planet that will be added into a larger space setting. The thing is, I want it to be plausible and interesting from a scientific perspective. However, having little scientific knowledge, I would like to get other's imput on the matter.

My idea is a rocky moon of a gas giant much larger than Jupiter. This moon vaguely resembles Mars, but is bigger, and with a breathable atmosphere. Water covers less than 20% of the planet mostly in liquid form. The planet hasn't develpped a native life except some microbes and tiny organisms. Then, humans came and began some terraforming in introducing plants and animals. However, this mostly remains a barren desert planet (inspired from Dune and Tatooine).

Now, to make things different I thought the atmosphere would be 12% oxygen / 30% nitrogen / 57% helium / 1% other (Earth: 21% Oxygen / 78% Nitrogen / 1% other). Then, the atmosphere would be thinner than on earth, so breathable air is mostly available in deep canyons or crateres, and other low altitude places. My idea is that people coming from Earth, when on this planet have the benefit of a lesser gravity, but having less oxygen would offset that benefit. Now this is but speculation on my part, and I would like to know what scientific-minded people think about it. Then, I am wondering what would be side-effects of having such a different atmosphere (aside from fires being more difficult to start, and life having less opportunities to develop). Also, would I need to make a denser atmosphere to shield the planet's surface from the gas giant's radiation?

Well, any imput welcome.

Henrix · Jul 15, 2006

I don't know if that atmosphere would be breathable, but with 57% helium I think people would talk rather funny.

(And get a sore and very dry throat.)

jeff37923 · Jul 15, 2006

Will this be a hot desert world (like Dune & Tatooine) or a cold desert world (like Mars & Siberia)? Personal protection will be very different depending on the temperature.

You might want to think twice about the helium in the atmosphere. Helium tends to be so light that it just drifts away from worlds unless it gets sucked in by a heavy gravity field (about 1.2 Gs or higher IIRC).

Turanil · Jul 15, 2006

Well, I want a relatively cold desert, but not freezing cold like Mars. I am thinking a temperate-cold desert world.

Hum, if helium tends to drift away, my idea is implausible... I chose helium because it is an inert gas... I wanted to create a different, yet breathable atmosphere.

LightPhoenix · Jul 15, 2006

Turanil said:
Hum, if helium tends to drift away, my idea is implausible... I chose helium because it is an inert gas... I wanted to create a different, yet breathable atmosphere.

The problem with that is basically that humans evolved on Earth, which is the NO atmosphere we know and love. Consequently, it's the atmosphere we're adapted to.

Oxygen in the air tends to be a somewhat tricky thing. On the simple side, oxygen won't generally be elevated in a successful atmosphere, because it is highly flammable. Also, at elevated partial pressures, oxygen can be toxic above 21%, but that's not really relevant to this discussion. Low concetrations of oxygen rapidly produce hypoxia. After a little research, 17% seemed to be considered the safe lower boundary. 12% would require oxygen tanks, I would think.

Also, in regards to inert gases, atmospheric nitrogen, as N2, is in fact inert. That is why we can't blow up our atmosphere. Not only is nitrogen inert, but it acts as a buffer, lowering oxygen concentration.

Finally, realistically, Helium in such great quantities isn't going to just be around, or stick around. As mentioned, it's a very light gas, and gravity likely wouldn't keep it down. Secondly, the primary form of helium production in the universe is through stellar fusion. Generally, helium on planets comes as a result of radioactive decay - pretty much the entire planet would have to be radioactive, pretty much nixing a breathable atmo.

Now, all that said:

Argon. The most abundant noble gas in Earth's atmosphere. Also found in quantity in Mars' atmo as well. It's heavier and will stick around in an atmosphere. It's also more likely to be around, as a radioactive byproduct of the breakdown of potassium isotopes in rocks (according to Wikipedia). High concentrations will still make an atmosphere unbreathable, but you could probably bump this up to maybe 10%, at the cost of some nitrogen.

Carbon Dioxide. You could bump this up, but it is very much not inert. Atmospheric CO2 will generally react to form acids, specifically IIRC carbonic acid when inhaled at high concentration. I couldn't find a number for a safe level though.

You might think sulfur (S) and phosphorous (P), beneath oxygen and nitrogen in the periodic table, would be decent substitutes. This is not so. Both are solids in pure form at room temperature. Further more, they are vastly more reactive.

Rodrigo Istalindir · Jul 15, 2006

How habitable do you want it to be?

The larger Jovian moons aren't much bigger than Earth's moon. You'll need to up the size or density considerably to get near-normal gravity, and you'll need that to have any hope of maintaining a usable atmosphere.

You'll need to postulate an ideal distance from the gas giant. Too close and volcanism and radiation from the parent will cook anything; too far and temperatures will drop to the point where there isn't a molten core (to generate a magnetic field) and it will be too cold.

diaglo · Jul 16, 2006

i'd propose having the humans bring some form of atmosphere/air conversion system with them on a large scale. they upgrade it as their community grows.

kinda like the desalination systems used on the oceans or seas for the areas with little drinkable water now.

also as a side effect they can mine the elements from the air they get as residue/waste. maybe even inventing equipment that will run on this waste. helium vehicles i guess.

jeff37923 · Jul 16, 2006

Turanil said:
Well, I want a relatively cold desert, but not freezing cold like Mars. I am thinking a temperate-cold desert world.

Hum, if helium tends to drift away, my idea is implausible... I chose helium because it is an inert gas... I wanted to create a different, yet breathable atmosphere.

OK. Temperate-cold thin atmosphere desert sounds like the Andes Mountains on Earth. Hmmm...

You could have had the world partially terraformed by hitting it with a few comets. The air would still escape over a few hundred years, but it would be breathable in deep canyons and craters. The 20% surface water could have come from the comets, filling the bottoms of the craters and canyons, with the oxygen-producing plants near the oasis of water.

I'd have to look at a pressure-temperature chart of water, but at low pressures water boils at very low temperatures. For a world with a low-pressure atmosphere, that atmosphere could be a mixture of water-vapor and carbon dioxide. The world would still not have any free-standing water, like a desert, but a character without a filter mask would drown in the air. Oxygen could be produced by microbial floating plants, adding to the need for filter masks.

Oh, someone earlier in the thread mentioned Argon as an inert gas. Its also the same gas used in flourescant lights and IIRC, it displaces air in confined spaces. Although it would be cool to say that there is a sizeable amount in the thin atmosphere due to a nuclear war from a previous civilization.
Tell me more about what you'd like for the world so I can provide more suggestions.

genshou · Jul 16, 2006

d20 Future has rules for low-gravity environments. D&D (and possibly other d20 System rulesets) have rules for high altitude, which would work for low-oxygen worlds in a pinch.

http://www.dominion-x.net/msrd_html/FutureEnvironments.html said:
LOW-GRAVITY ENVIRONMENTS
In a low-gravity environment, the pull of gravity is significantly less than what we experience living on Earth. Although an object’s mass doesn’t change, it becomes effectively lighter. This means that creatures bounce when they walk. It becomes easier to move and lift heavy objects as well as perform Strength-related tasks. In addition, creatures take less damage from falling.
Speed: A creature’s speed increases by +5 feet in a low-gravity environment. This bonus applies to all of the creature’s modes of movement.
Carrying Capacity: A creature’s normal carrying capacity is doubled in a low-gravity environment. In addition, the creature gains a +10 bonus on any Strength check made to lift or move a heavy unsecured object.
Skill Check Bonuses: Creatures in a low-gravity environment gain a +10 bonus on Strength-based skill checks (including Climb, Jump, and Swim checks).
Attack Roll Penalty: Creatures take a –2 penalty on attack rolls in a low-gravity environment unless they are native to that environment or have the Zero-G Training feat.
Damage from Falling: Creatures do not fall as quickly in a low-gravity environment as they do in a normal- or high-gravity environment. Falling damage is reduced from 1d6 points per 10 feet fallen to 1d4 points per 10 feet fallen.
Long-Term Effects: Long-term exposure to low-gravity conditions can cause serious problems when returning to normal gravity. A creature that spends 120 hours or more in a low-gravity environment takes 1d6 points of temporary Strength damage upon returning to normal gravity.

http://www.d20srd.org/srd/wilderness.htm#mountainTravel said:
Mountain Travel
High altitude can be extremely fatiguing—or sometimes deadly—to creatures that aren’t used to it. Cold becomes extreme, and the lack of oxygen in the air can wear down even the most hardy of warriors.

Acclimated Characters
Creatures accustomed to high altitude generally fare better than lowlanders. Any creature with an Environment entry that includes mountains is considered native to the area, and acclimated to the high altitude. Characters can also acclimate themselves by living at high altitude for a month. Characters who spend more than two months away from the mountains must reacclimate themselves when they return. Undead, constructs, and other creatures that do not breathe are immune to altitude effects.

Altitude Zones
In general, mountains present three possible altitude bands: low pass, low peak/high pass, and high peak.

Low Pass (lower than 5,000 feet)
Most travel in low mountains takes place in low passes, a zone consisting largely of alpine meadows and forests. Travelers may find the going difficult (which is reflected in the movement modifiers for traveling through mountains), but the altitude itself has no game effect.

Low Peak or High Pass (5,000 to 15,000 feet)
Ascending to the highest slopes of low mountains, or most normal travel through high mountains, falls into this category. All nonacclimated creatures labor to breathe in the thin air at this altitude. Characters must succeed on a Fortitude save each hour (DC 15, +1 per previous check) or be fatigued. The fatigue ends when the character descends to an altitude with more air. Acclimated characters do not have to attempt the Fortitude save.

High Peak (more than 15,000 feet)
The highest mountains exceed 20,000 feet in height. At these elevations, creatures are subject to both high altitude fatigue (as described above) and altitude sickness, whether or not they’re acclimated to high altitudes. Altitude sickness represents long-term oxygen deprivation, and it affects mental and physical ability scores. After each 6-hour period a character spends at an altitude of over 15,000 feet, he must succeed on a Fortitude save (DC 15, +1 per previous check) or take 1 point of damage to all ability scores. Creatures acclimated to high altitude receive a +4 competence bonus on their saving throws to resist high altitude effects and altitude sickness, but eventually even seasoned mountaineers must abandon these dangerous elevations.

Turanil · Jul 16, 2006

jeff37923 said:
Tell me more about what you'd like for the world so I can provide more suggestions.

Well, I want a world reminding of Tatooine, Dune, and Mars.
-- I see it a desert world with no more than 20% water covering it. It must sustain some populations.
-- No native life except microbial; everything (plants, animals, etc.) has been imported by colonists.
-- I want humans able to walk on it without special equipment, yet I thought it would be cool if it was restricted to low areas like canyons, deep valleys, etc. Everywhere else a mask would be required.
-- I want the planet somewhat bigger than Mars, but smaller than Earth. It would have lesser gravity than Earth, but not something making humans who come here too strong.
-- I want it orbiting a gas giant larger than jupiter, the latter at something the orbit of Mars, so it's not too cold and too dim (heat coming from both gas giant and sun). Maybe the planet is tidally locked to the gas giant. So there would be long days and nights.
-- Humans get some helium-3 for energy fuel from the gas giant. There are other moons orbiting the gas giant so there are inhospitable world close with bases, mining, etc. One of the moon should have very low gravity, but a thick atmosphere with totally alien life forms of drifting creatures in the sky (after a painting by Mac Garlick).