I just rolled up the most horrendous "habitable" planet ever.

[David Johnston2]

Cauchemar: 0.35: Standard (Garden) 265 (BB) 61% hydrosphere, 1.01 density, 0.83 diameter (6,554 miles), 0.83 gravities, 0.57 mass, Thin Breathable Atmosphere (0.58 atmospheres), -0.4 eccentricity, 253 degrees (Very Cold), Perihelion 0.21, Aphelion 0.56. Tidal Force 3.1, 282 days per day, 107 days per year, 5 degree axial tilt, Light Volcanic Activity, No Tectonic Activity, RVM -1, Habitability 5

The "average temperature" is Frozen, but during its 9 and a half month long day the current day side really heats up, and every 3 and a half months it gets close enough to the sun to sterilize the tropical zone and boil the oceans.

It's the most uninhabitable habitable planet I've ever seen.

[Johnny1A.2]

Originally Posted by David Johnston2

Cauchemar: 0.35: Standard (Garden) 265 (BB) 61% hydrosphere, 1.01 density, 0.83 diameter (6,554 miles), 0.83 gravities, 0.57 mass, Thin Breathable Atmosphere (0.58 atmospheres), -0.4 eccentricity, 253 degrees (Very Cold), Perihelion 0.21, Aphelion 0.56. Tidal Force 3.1, 282 days per day, 107 days per year, 5 degree axial tilt, Light Volcanic Activity, No Tectonic Activity, RVM -1, Habitability 5

The "average temperature" is Frozen, but during its 9 and a half month long day the current day side really heats up, and every 3 and a half months it gets close enough to the sun to sterilize the tropical zone and boil the oceans.

It's the most uninhabitable habitable planet I've ever seen.

I wouldn't consider it to be habitable at all. To my mind, a habitable world is one where humans (or whatever species) could, at least in theory, survive and reproduce open-ended without technological support (i.e. like Earth). I'm not sure TL0 humans could do that on this world.

(With the right technology and support, any world is potentially habitable.)

[Ulzgoroth]

Is generating a day longer than the year valid? I thought per the text on Space p118 that should be interpreted as tide-locked or perhaps resonant?

Originally Posted by Johnny1A.2

I wouldn't consider it to be habitable at all. To my mind, a habitable world is one where humans (or whatever species) could, at least in theory, survive and reproduce open-ended without technological support (i.e. like Earth). I'm not sure TL0 humans could do that on this world.

(With the right technology and support, any world is potentially habitable.)

Without technological support is asking a lot..

[The Colonel]

Reminds me of that planet from the old 2300AD supplement "Kafer Dawn" - tidally locked with the settlements on a thin equatorial belt, vicious tidal activity and a non-compatible biota.

[Varyon]

Originally Posted by Ulzgoroth

Without technological support is asking a lot..

Yeah, Habitable should be more "life similar to what we're used to can evolve here naturally." Many interpretations of how life would evolve elsewhere would, if using the definition of "Humans and similar can survive here without technological assistance," have only Earth as habitable - because we wouldn't be able to eat anything on a planet that evolved its own life. Here's an example from the recent Q&A for the webcomic Runaway to the Stars. Heck, you don't even need to go that extreme - in the web serial The Deathworlders, where everyone being able to eat each other's food is the norm (Earth crops become popular due to their high nutritional density compared to most others), a crew of humans get stranded on what is considered in-setting to be an extremely high-habitability planet (I think something like Class I or Class II, where most sophonts could be set down naked with no training or gear and thrive without issue), but the simple native plants are primarily cellulose (or at least a cellulose analogue), which humans cannot digest (the bulk of sophonts in the setting are herbivores and can digest it without issue), leaving them to starve once their food runs out (or it would have, if the Hunters weren't using it as a safari world to breed sophonts for eating; all the humans who survive to make it off-planet become strict vegetarians once they're back in human space, but while there they have no choice but to kill and eat other sophonts).

[ericthered]

Most of the problem, I think, is the eccentricity. Frozen happens, tidelocked happens, low pressure happens, but I think the eccentricity makes all of that except maybe the tide-locking irrelevant. This planet is probably something other than garden.

[Stormcrow]

It's an example of what GURPS Space calls a "changing world": specifically, one where "the world is subject to regular, cyclic changes in its environment," good for stories "emphasizing adaptability in individuals or societies." Another example is the planet Trenco from the Lensman series: during the day the surface boils to a gas; during the night it condenses into a liquid. To say it rains there at night is a massive understatement. The people who go there do so to obtain thionite, which is used to create a potent drug, and they go to great lengths to endure the changing cycles of the planet in order to get it.

[David Johnston2]

Originally Posted by ericthered

Most of the problem, I think, is the eccentricity. Frozen happens, tidelocked happens, low pressure happens, but I think the eccentricity makes all of that except maybe the tide-locking irrelevant. This planet is probably something other than garden.

The eccentricity alone would not be that big a deal with a thicker atmosphere. It would just create rapid seasonal cycling with longer winters than summers. The eccentricity combined with days that last for months and the thin atmosphere creates gigantic cyclical temperature extremes,

[dcarson]

Cycle of Fire by Hal Clement has a planet with a long eccentric orbit so it changes every so many generations. So two seperate very different ecologies which in many cases are dormant spores or such in the other ecology lifeforms. So when it heats up enough the lifeform dies and the spores use the biomass to get a head start at growing.

[RyanW]

Originally Posted by Ulzgoroth

Is generating a day longer than the year valid? I thought per the text on Space p118 that should be interpreted as tide-locked or perhaps resonant?

Rotational period can't usually be longer than the year*, but the length of a day (synodic period) takes into account rotation and revolution around the primary. With Earth-like motion the effect is pretty minimal (Earth has a rotational period of 23 hr 56 minutes), but when rotation and revolution get closer, it gets more significant. Mercury has a rotational period of 58 earth days but a day length of 176 days (2 local years).

* Venus has a rotational period longer than its year, but it rotates backwards, so it isn't anywhere near tidelocking.