Are geographically typed planets realistic?

I think it is totally plausible for there to be planets with a single kind of terrain. For this to happen, the whole surface of the planet must be at roughly the same temperature (unless you're talking about a desert planet and allow different types of desert). This doesn't happen on Earth: the poles are much colder than the equator. The situation is even worse on Mars, in terms of the temperature differential between the poles and equator. On Venus the entire surface is indeed at about the same temperature. This is because Venus' thick atmosphere and strong winds are so efficient at redistributing heat across the planet's entire surface that any temperature differences are smoothed out.

Like Venus, I think a planet with habitable conditions could have a relatively uniform surface temperature. With a thick enough atmosphere the surface temperature would be relatively homogeneous (in detail, this also depends on things like the atmospheric composition and spin rate). I don't see why you couldn't have a planet like Dagobah, with a thick atmosphere that maintains jungle-like temperatures across the whole planet. Or a water world that is a global ocean with similar temperatures.

Since a thick atmosphere often has a significant greenhouse effect, a planet with a uniform surface temperature would likely be relatively far from its star, in the outer parts of the habitable zone. In the most extreme case you could imagine a free-floating planet with no star. It's plausible that such planets could have life, either under a thick hydrogen atmosphere or in an ocean under a thick layer of ice (see here: https://aeon.co/essays/could-we-make-our-home-on-a-rogue-planet-without-a-sun or here: https://planetplanet.net/2015/06/04/real-life-sci-fi-world-8-the-free-floating-earth/)

posted over 8 years ago

Sean Raymond‭

31 reputation 0 2 3 0

I'm going to take one of your examples here: the desert planet. Is that realistic and plausible?

It turns out that it is realistic. Wikipedia describes a desert thusly:

A desert is a barren area of land where little precipitation occurs and consequently living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation.
...
Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks which consequently break in pieces.

Desert climate is described as:

Desert climate (in the Köppen climate classification BWh and BWk, sometimes also BWn), also known as an arid climate, is a climate that does not meet the criteria to be classified as a polar climate, and in which precipitation is too low to sustain any vegetation at all, or at most a very scanty shrub.

Polar climate is defined primarily by the lack of warm summers:

Every month in a polar climate has an average temperature of less than 10 °C (50 °F).

It turns out that the above description of desert climate sounds like a pretty decent description of Mars' climate. Mars' large orbital difference between perihelion and aphelion creates constant thermal stress, which the thin atmosphere does little to reduce; temperature swings of nearly 200 Kelvin are seen between the extremes on the surface and between summer and winter, whereas summer daytime temperatures of around 35°C have been measured. Mars also shows a fairly large difference between daytime and nighttime temperatures, which is a property typical of desert areas, but I cannot seem to find any specific figures at the moment.

posted about 10 years ago

4y ago

Canina‭

569 reputation 35 72 69 40

Planets which have something that we might consider to all be a single climate given the way we classify things based on earth is entirely plausible, for certain climates at least.

Mars easily qualifies as a desert over its entire surface. There is climate variation, but all of it is something we would call "desert".

Similarly, you could have more water to the point it covers everything and the entire planet would be ocean (which isn't exactly a climate in and of itself). But oceans can have varying climates. Variations based on depth, insolation, currents, etc. The intertropical convergence zone would likely be a massive band band of thunderstorms. Then you'd have calm doldrums, and then utterly mid latitudes where massive hurricanes sweep across periodically.

A global swamp or jungle though doesn't seem workable. A global wetland would need an almost perfectly smooth planet where everything was in an absolutely perfect balance. "Jungle" is fairly specific and tied to the specific nature of life on the planet. Both global jungle and global wetland have the severe problem of where you maintain a reservoir of water to generate the rain with oceans.

Making a single climate planet habitable is also problematic. Without phytoplankton and forests, a desert planet isn't going to have an oxygen rich atmosphere, unless you do something strange like the Sand Worms of Arrakis in Dune which produce ridiculous amounts of oxygen. Then again they are generally just ridiculous creatures so you might as well just declare that where the oxygen comes from is irrelevant to the story. One might say that Arrakis isn't functionally a desert for its native life because lack of water is irrelevant to them.

What makes a place a "functional desert" is extreme scarcity of a resource life needs, but which can be gathered, retained, and re-used. Most likely a solvent or other medium within which biological chemistry occurs. It's improbably that life would originate on a planet which is entirely functionally desert for that life.

posted about 10 years ago

smithkm‭

21 reputation 4 2 2 0