Gigantica -- A Study in Maximum Habitable Planet Size

[MrBragg]

Your precipitation seems really strongly seasonal, and the almost complete lack of rain anywhere in the north during its winter feels a little off. The south also seems like it should be wetter in the winter, though I'm not sure how much of an effect your significantly increased radius would have on any of this.

A minor point, but your -75 C mountain range in the north is cold enough to start freezing CO2, so those must be some crazy high mountains

[Naima]

Very nice job so far, On the precipitation I too have some doubts about those, I do not seem to recognize any major rainshadow effect or may be I am misinterpreting the color code map ?
As for the size f the earth as long as the earth has the same or similar composition making a planet a superearth would keep still the same natural gravity because the surface despite the increase of the mass would be at a maor distance from its nucleus the formula for calculating a planet’s surface gravity: mass divided by the radius squared. That is, SG=M/R^2. If you express mass and radius in Earth units, you get surface gravity as multiples of Earth's as the greater the planet’s radius is for its mass, the less dense it is.
source
https://phl.upr.edu/projects/habitab...lanets-catalog

[Peter Toth]

First of all, a cordial “thank you” to everyone who provided feedback to this work in progress. Your critiques are very important to me, as I rely on them to produce better quality cartography.

Yes, MrBragg and Naima, the precipitation I derived using Azelor’s tutorial gave very anomalous results; and furthermore fails to account for any rain shadows. This is probably due to steps that I missed somewhere along the line. (That memory of mine is severely faulty when I’m executing complex processes, lol; thus, I’m more comfortable relying on a software GCM than these procedural algorithms.) Moreover, the final topography hasn’t yet been finalized, (I wanted to generate climates to determine mountain erosion and river flow first), so any rain shadows would likely change after I’ve reached this end point.

Yes, MrBragg, the temperature at the top of those mountains is -75 Celsius, which doesn’t sound realistic to me at all. I based that calculation using a lapse rate of 10 degrees per kilometer, instead of 6.5 in the case of the Earth, simply because Universe Sandbox had output the unusual value in its independent calculation of lapse rate. In retrospect, I probably should have stuck with Earthly values, for I certainly don’t want to destabilize the carbonate-silicate cycle by freezing CO2 on the surface.

To answer your question, Naima, the dimensions of Gigantica do accord with the equation you provided. I generated them using the Wolfram Manipulate Planet app on the Worldbuilding Pasta site, which uses central pressure and composition to determine a planet’s dimensions. I wanted to derive the particulars singlehandedly, but became very daunted when my calculus yielded a margin of error that was unacceptable to me. Mass and radius are below. (By the way, MrBragg, did you ever figure out that page describing this process, that I sent you several months back?)

Mass: 1.361 Earth masses
Radius: 7,359 km

Earlier, I alluded to feeling uneasy relying on procedural algorithms for determining climatic details, especially complex ones such as rainfall. Unfortunately, Clima-Sim, which in my opinion is the best software program suited for modelling a planet’s climate, doesn’t calculate rainfall values; moreover, its maximum output is rather crude.

Thus, in the last couple weeks since my last post, I finally succeeded installing and configuring ExoPlaSim. After over a dozen hours of trial-and-error programming, I was at last able to get my simple T21 model working. (Almost threw the computer out my window, too.) The results of ExoPlaSim’s handiwork can be seen at the bottom of this page.

Unfortunately, upon simply changing the model of the script to T42 (leaving everything else the same), the program crashed immediately for a reason I couldn’t diagnose. Curiously, when I inserted my flash drive and recompiled the script, it computed for a few seconds, but then froze for over an hour before I forcibly terminated the script. Does anyone out there with Linux experience know how to run a T42 resolution model successfully? If it makes any difference, the scripts on Worldbuilding Pasta always crashed for me; I had to copy the ones on the ExoPlaSim manual before I had a working program.

At bottom are the graphics provided thanks to ExoPlaSim (and Photoshop, which I used to modify the gradient and add a posterize adjustment layer). I realize the range in temperatures between summer and winter across latitudes is rather insignificant and may be undercalculated; I assume this is a result of my shorter year at 243.7 Earth days. Please let me know if you agree; the orbital elements are below:

Flux: 1,329.7 W/m2
Star Temp: 5,319 K
Year Length: 243.7 earth days
Eccentricity: 0.01774
Rotation Period: 19.62 earth hours
Obliquity: 26.38 degrees
Gravity: 10.0267 m/s2
CO2 Partial Press: 0.000351 atm
Total Atm Pressure: 1.324 atm

Sea Ice January:



Sea Ice July:



Surface Temp January:



Surface Temp July:



Sea Level Pressure January:



Sea Level Pressure July:



Precipitation January:



Precipitation July:



By the way, does anyone know why ExoPlaSim doesn't provide a scale for its precipitation values, yet can plot precipitation intensity over the globe?

At any rate, using your feedback, I hope to eventually master the ExoPlaSim program.

Thank you again.

Peter

[worldbuilding pasta]

Were you using the same topography input files for the T21 and T42 runs? Every resolution needs unique topography and landmask files.

Exoplasim reports the precipitation in units of m/s, which for a typical value of like 30 mm/month would be 0.000000011, so Panoply is showing a scale but the labels are rounded. If you check the koppenpasta repository, I recently added a new script for averaging outputs together that also has a function for converting the precipitation to more convenient units.

[Peter Toth]

First of all, thank you, worldbuilding pasta, for the very useful tip. As it turned out, I WAS using the T21 topography input files when I should have created a new set for the T42. I'll be sure to remember this in future simulations.

Thanks also for explaining the issue with the precipitation; I'll definitely make use of that script you referred to.

Here's my latest progress for my first continent, with and without the texture map.





In case you're interested, I used Wilbur and Photoshop to create these images.

To all experienced cartographers, please let me know if I'm anywhere close to my goal of rendering realistic topography. I'm considering using a real DEM in case the vote is a "no."

Thanks!

Peter

[Naima]

First of all, thank you, worldbuilding pasta, for the very useful tip. As it turned out, I WAS using the T21 topography input files when I should have created a new set for the T42. I'll be sure to remember this in future simulations.

Thanks also for explaining the issue with the precipitation; I'll definitely make use of that script you referred to.

Here's my latest progress for my first continent, with and without the texture map.





In case you're interested, I used Wilbur and Photoshop to create these images.

To all experienced cartographers, please let me know if I'm anywhere close to my goal of rendering realistic topography. I'm considering using a real DEM in case the vote is a "no."

Thanks!

Peter

Seems good but not sure of the scale, if its like a continent I think the rivers are too big if you want realism while if you want them visible or , just that big then are fine .

[Peter Toth]

Hello Guild,

Thanks for the feedback, Naima.

Because I'm personally not satisfied with the results of my Wilbur approach, I've decided to use morne's method of juxtaposing actual DEM data to create a more realistic topographic map. It may take longer, but I'm aiming a bit higher this time around.

But first, I've run into some problems. Calculating my climates using worldbuilding pasta's script, I've discovered that much of my world will be covered in cold icecap climates and thus remain uninhabitable. Here are two maps comparing my initial parms to Earthlike parms. I'm definitely in favour of the Earthlike parms, but a 24 hour day is much too long to generate an adequate magnetic field for atmospheric protection.

Initial Parms:



Earth Parms:



Is there anything I can personally do to the parameters to make more surface area of my planet livable? Must I speed up the rotation or increase atmospheric density? I didn't want to increase the insolation as I already have average temperatures of 40 C in some regions. What other parameters could I change to ensure a more congenial spread of climates?

Thank you for any suggestions!

Peter

[MrBragg]

I've not used ExoPlaSim yet, but my understanding is that its output can depend quite strongly on input resolution of the topography (especially for the lower resolutions), so it may be worthwhile trying T42 or T63 if you have the time / CPU power to devote to that. It might turn out that your parameters aren't as bad as this low res simulation makes it seem.

[worldbuilding pasta]

I can confirm that T21 models routinely come out 5-10 C colder than T42 models. T63 might be a couple degrees warmer than T42, but I haven't tested it enough to be sure, and it can't be that big a difference given that T42 pretty reliably replicates the average temperature of modern Earth. I think it might have something to do ice albedo feedbacks over the larger cell size.

But for future reference, the usual approach to warming the polar regions without warming the tropics would be to increase the axial tilt.

[Peter Toth]

Hello Guild,

I've finally been able to run the T42 model and I'm very impressed with the capabilities of ExoPlaSim. One snag, however: my Koppen climate script pretty much duplicated the results of the T21 run, despite its higher resolution. I had hoped for warmer temperatures poleward to make the climate there more congenial and livable. I was leery about increasing the axial tilt, especially when, toying with the feature in Clima-Sim, I noticed that the higher axial tilts do not distribute heat evenly across the globe but rather increase the range of temperatures. (The winter temperatures became a bit too frigid for my tastes with greater obliquity.) So I'm wondering if raising the atmospheric pressure might help distribute the heat across latitudes, or perhaps slowing down the rotation a bit.

A comment for worldbuilding pasta: I tried to use the script for converting precipitation units into a more usable form but kept getting this error message after two prompts (the first specifying the month offset; the second, the longitude offset):

Month Offset
Offsets output forward an integer number of months compared to input files
e.g. if a file starts in November, an offset of 2 will shift the start to January
Offset ("0" for no offset): 0

Rotate Longitudes
Convert longitudes from [0,360) range to [-180,180) range
with 0 longitude where 180 longitude formerly was
Rotate (y/n): n
Traceback (most recent call last):
File "eps_avg.py", line 83, in <module>
if rotate in ('y') or ann_avg in ('1'):
NameError: name 'ann_avg' is not defined

Can you diagnose the problem?

Finally, here are some screenshots of the T42 resolution. I'll probably revise the parameters until I get a more congenial spread of temperatures across the latitudes.

First, the Koppen map:



Northern Summer Temperatures:



Northern Winter Temperatures:



Northern Summer Precipitation:



Northern Winter Precipitation:



Northern Summer Pressures:



Northern Winter Pressures:



Northern Summer Wind:



Northern Winter Wind:



At any rate, please let me know what you think. Would raising the atmospheric pressure even out the temperature extremes from equator to pole? Would it also increase precipitation, knowing that air has a greater heat holding capacity at greater pressures? I specially appeal to anyone with an expertise in meteorology.

Thank you so much!

Peter