Help from knowledgeable ENworlders about biology/chemistry/astronomy

[Mycanid]

By the way Turanil - its nice to see that you haven't gone away.

I like your proposed ideas about the planet. I wish I could help more with them. though, realistic wise.

Two possibilities come to mind:

1. Have a race that looks like humans but is not

2. Have the humans living underground or in artificial environments somehow.

Maybe these might help jumpstart an aspect of your ideas somehow????

Anyway, like I said. It's good to see you still "about".

 

[Ed_Laprade]

I'm sorry, but a desert planet that Humans can live on (as in a permanent colony without special equipment needed) just ain't gonna happen. Without a LOT of plant life any oxygen in the atmosphere would have to be 'imported', and wouldn't remain free for long. (Turned into CO2, rust, etc.) It would definitely need a magnetic field, or everyone gets fried by the radiation from the gas giant. If you want a planet like that it'll have to be in the early stages of terraforming, as someone else suggested.

 

[jeff37923]

I'm sorry, but a desert planet that Humans can live on (as in a permanent colony without special equipment needed) just ain't gonna happen. Without a LOT of plant life any oxygen in the atmosphere would have to be 'imported', and wouldn't remain free for long. (Turned into CO2, rust, etc.) It would definitely need a magnetic field, or everyone gets fried by the radiation from the gas giant. If you want a planet like that it'll have to be in the early stages of terraforming, as someone else suggested.

Ed's pretty much right on the money (I'd argue the radiation from the gas giant part because it would depend on the gas giant and the star it orbits). Something to remember though, we have not yet found another world that could be considered to be even marginally habitable for terrestrial life. The only known habitable world is Earth. So for the purposes of a game setting, the world just has to be plausable - it doesn't have to be scientifically perfect.

Just some examples of plausible worlds from science fiction - Rocheworld, Jinx, We Made It, Canyon, Plateau, Asimov's Mercury (from the short story Runaround), Heinlein's Ganymede (from Farmer in the Sky), and many more. Each of these worlds is plausable according to the science of the time - but as settings for stories, they are great.

 

[Fenris]

Indeed, traditional views of terraforming consist of the introduction of non-native, oftne invasive plants intot he new environment (whether terrestrial or another planet).

If you want plants to grow you will need some carbon dioxide in the air. Enough plants can generate the oxygen you need. May I suggest that in addition to your native microbes you add some primitive lichens. They would be able to survive the cold and dry conditions, but during the once-a-year rain storm, they could flourish and thus justify why you have any oxygen there at all (unless the planet used to have more water).

The other nessecity for both a heavier gravity field and more oxygen is of course ozone. Without a decent ozone layer, the humans will not be able to move around without special equipement (SPF 2,000 doesn't count ) Not even restricting life to canyons will help that.

One thing to consider in regards to plants and temperature in general is the rotation of the planet around it's star and the rotation of the moon around the planet and the rotation of the moon itself. How much light and dark time will you have? Too much time behind the gas giant will cool the planet too mcuh for life, too much time in front of it could heat it up. I see wide temperature swings here. Maybe life is restricted to the poles where the temperature swings aren't as bad.

 

[wingsandsword]

For making a mostly desert planet an at least somewhat plausible idea, the best suggestion I ever came across was in an old Star Trek novel, trying to explain the ecology of Vulcan.

Since all the canonical examples we've seen of the planet are of a harsh, hot desert, and it's notably hotter than Earth, with lower oxygen levels (enough to affect human performance, but enough to at least live on day-to-day), and much less free water, how could it sustain atmospheric oxygen?

The solution the author had was at the poles, which given a good axial tilt should be notably cooler than the rest of the planet, and there would be forests, polar forests that provide oxygen instead of ice caps.

Now, since you don't want any native life above microbes on this planet at this point, that's not really so much of an option (but a possible idea planned for future terraformers).

 

[Turanil]

First, thanks to everybody for your answers, which are useful.

Now about O2, if I understood what I did read (see below), it's not absolutely required to have plant life to produce O2 in the atmosphere. A hot planet with a lot of water evaporation could have enough oxygen in the atmosphere through photodissociation of water vapor. So, let change from cold desert-like planet to hot; maybe this could fit: I will use a sun-like star but older; through time its luminosity-radiance augmented, which led to the planet losing much of its water (that was turned into oxygen). Now the planet orbits around a gas giant, so being close to the inner Habitable Zone edge, it will be hot enough so it doesn't become too cold when behind the gas giant. Also, it will have most of its remaining water on the poles as suggested above. Otherwise, it will have a strong magnetic field, so probably be geologically active (as on Earth).

The reason that the HZ is important is two-fold: First, it indicates where inhabited planets might be found. And, second, it provides useful information about abiotic production of O2. The only net abiotic source for O2 is photodissociation of H2O, followed by escape of hydrogen to space. The rate at which this occurs is governed by the mixing ratio of H2O in the stratosphere, according to the principle of diffusion-limited flux (2,3). For Earth, the stratospheric H2O mixing ratio is small (~4 ppmv), and the corresponding O2 production rate is only ~5 x 107 O2 molecules cm-2s-1. This is about 400 times smaller than the rate of O2 production by photosynthesis followed by organic carbon burial (4) and about 100 times smaller than the rate of O2 consumption by reaction with reduced volcanic gases (5). Thus, Earth's atmosphere would be virtually anoxic in the absence of life (3,6). A planet near or inside the inner edge of the HZ, however, could have a much higher stratospheric H2O mixing ratio and a correspondingly larger abiotic O2 source (1). Venus, for example, could have accumulated tens or even hundreds of bars of O2 during the time that it lost its water (7). Thus, the identification of O2 in a Venus-like planet's atmosphere would not necessarily indicate that life was present.

 

[Fenris]

The problem with that though is that you lose the hydrogen. Once the oxgen is in the atmosphere there is no way to get it back down to become water again. It's a one way equation that results in the depletion of water from the planet's surface. Now if you had enough ice buried under a cold planet or at the poles it may work.

BUT once you add humans on the surface and they start consuming the scant oxygen supplies, just from breathing not to mention the consumption of oxygen for their machinery, you will quickly deplete the atmosphere of oxygen and abiotic production will not be able to keep up.

Now if you use abiotic to justify why oxygen is present to begin with, and then introduce terran plants afterwards, you can set up a sustainable system, if enough plants are present.

My concern with photodissociation however is that the energy required to cuse a sufficent build up of oxygen would still be too much for plants and especially for people. If you have to bombard the planet with 400 times the solar energy of earth to generate enough oxygen, nothing Terrestrial will survive on that thing.