Let's make a list of plausible, habitable exomoons/planets

[Czcibor]

Aim: create a thread for prospective writers, which kind of planet/moons is possible to set their story. The best are the cool and exotic (exotic for an Earthling) ones - "floating mountains" - forbidden. Tidally locked - OK.

Conditions: a ship wrecked astronaut would not be immediately doomed. So atmospheric oxygen is required, and temperature / pressure would have to be survivable.

This thread serves as a place brainstorming. In final version it would be somewhat summed up, backed with links to articles/publications and linked to list of SF materials.

Idea 1:
Planet orbiting red dwarf.
-Planet is tidally locked (so one side is grilled, the other frozen)
-if the heat transfer is not good enough there is a risk that atmosphere would froze on the cold side
-in consequence to avoid that planet would have to better have dense atmosphere / hydrosphere
-there would be a permanent hurricane in the part closest to its star, the habitable part would be a ring outside it
-assuming that I did no calculation error with Rayleigh scattering the sky would be orange
-the orbit should be almost perfectly circular (it would be a tendency for such shape, unless there is some heavy planet nearby that elongate the orbit)
-Star might be a flare star. A flare is a sudden period (like 10 minutes), when star become much more luminous. All living creature hide from heat weave and UV radiation. (pending on ozone layer, atmosphere thickness and story requirement so on it be something between desperate looking for cover or just a nuisance)
-such stars can keep similar luminosity for many times more than contemporary age of universe. Planet could have archaeological artefacts from prior civilizations. (sure improbable, but makes a good story)
-Such planet shouldn't have a moon. There is a star really nearby, so there is not much place for a stable orbit far away, while a close moon would be in case of such slowly rotating planet suffer to orbit decay and crash sooner or later in such planet.

suggested reading/watching:
Extraterrestrial Aurelia:

Idea 2:
Moon of a gas giant
-for story purposes almost like a planet (can be used in conjunction with other ideas)
-if the moon is very close to its planet it is going to have really powerful volcanic activity (like Io)
http://en.wikipedia.org/wiki/Io_(moon )
-if its far away it is safe... except that it is tidally locked to its planet, and like Calisto can have 16,5 days long day. (think about heating during day and cooling during night)
-one side of the moon sees its planet all the time, the other - never
-the planet may be at verge of usual habitable zone and heated a bit by tidal heating
-realistically speaking moon should be a bit inclined, so would not be eclipsed each time it goes behind planet.
-if story requires that the moon can theoretically be exactly within the same plane with planet. Day on one side would be interrupted each midday, what could even make this side slightly colder
-There can be more than one habitable moons. Such idea is terribly improbable, however still more realistic that two habitable planets in one system.

Ideas to be worked out: planet on elliptic orbit/moonless quickly rotating planet/ tilted planet /hot and dry planet with habitable polar regions/ planet around red dwarf in 2:3 resonance Loose ideas to be used:
-If there is denser atmosphere than water boiling temperature is different. In case of 2 atmospheres, water boiling temperature is around 130 C.
-Without humans (or any other sapient species) there should be big animals on a virgin planet. It seems that our cavemen ancestors slaughtered such big animals http://en.wikipedia.org/wiki/Megafauna#Megafaunal_mass_extinctions
-Local life is presumably unedible (different amino acids, different chirality and so on). Solutions for astronaut:
a) take part in soft SF, where there is no problem with that
b) assume panspermia and we have common ancestors with local life
c) cause a natural disaster, exterminate local life and replace it with Earth one
d) turn local life into simple organic molecule where it does not matter - alcohol (solution for Russian cosmonauts) ;)

 

[vemvare]

I think a planet with a significantly higher orbital eccentricity than Earth would be an interesting concept, the planet would have "planetary seasons" caused by varying distance to its star as opposed to our "hemispherical" seasons caused by axial tilt.

An astronaut crash-landing on a planet known to be habitable could use a bio-synthesizer, a not-so little device capable of turning organic material into syngas, syngas to methanol, then methanol in turn into edible protein, fat, carbs, which would then be neatly made into various foods.

 

[Czcibor]

I think a planet with a significantly higher orbital eccentricity than Earth would be an interesting concept, the planet would have "planetary seasons" caused by varying distance to its star as opposed to our "hemispherical" seasons caused by axial tilt.

Yes, I also thought about it. I still think how to combine axial tilt and elongated orbit

An astronaut crash-landing on a planet known to be habitable could use a bio-synthesizer, a not-so little device capable of turning organic material into syngas, syngas to methanol, then methanol in turn into edible protein, fat, carbs, which would then be neatly made into various foods.

That's cheating which spoils good story ;)