Realistic Earthlike Planet--Almagest

[Peter Toth]

Hello to all cartographers!

I'd like to introduce a conworld I've been working on for over a month; however, the map that follows represents only a minuscule portion of the work I've done. I've attended to various features of this world using rigorous mathematical calculations, factoring in plate tectonics, interior composition, atmospheric composition, insolation, meteorology, and descriptions of the neighbouring planets (for added realism). If you are interested in my work and want to see the full project, visit: www.compellingconworlds.com.

First of all, a brief description of Almagest's basic properties:

Mass: 1.0427 Earth masses
Radius: 6,606 km
Density: 5.179 g/cc
Gravity: 0.972 g's
Percent Silicate: 84%
Percent Iron (core):16%
Iron core radius: 2,787 km
Rotation Period: 26.1774 Earth hours
Axial Tilt: 21.65 degrees

Here's Almagest:

Almagest Low Rez.jpg

The colouring scheme I've used represents altitudes, which should be self-explanatory; I've avoided undersea bathymetry because of its time-consuming nature and its lack of prime importance.

I thought I'd specify that the north and south poles seem distorted, for this is the equirectangular projection. This is what the planet looks like from space:

Planet.jpg


Please criticize this conworld mercilessly, for I sincerely need the constructive criticism to improve my craftsmanship.

Thank you.

Peter

[AzureWings]

Qualitatively I think the geography is rather intriguing for further development (i.e. biomes and eventually resulting shape of cultures and nations, should that be the direction your conworlding decides to go) - it looks plausible on a gut feel while being very distinct from Earth's - although I wonder about the structure of the tectonic plates that produced so many north-south mountain ranges near the central part (not that I'm doubtful - don't know nearly enough about plate tectonics to draw any conclusions one way or another, just that at first glance it looks like there must be a lot of long narrow plates next to each other which sounds a little odd). I was going to ask about the uniformity of the oceans' central parts before I noticed your comment on eliding much of the undersea detail; I do want to note that it looks like you've got some regions of subtle horizontal-line artifacts in the western-hemisphere ocean that I don't think were your intent (to the left of what I think is a trench, although the shade is really similar to the surrounding water and hard to make out).

I'm not in a great position to really evaluate the plausibility of the numbers, but I ran a few quick ratios and there seemed to be some slight deviancy in the expected values:

- Density is 5.179 g/cm^3 compared to Earth's 5.513 g/cm^3 (assuming I read your units right). These should be proportional to planet mass / radius^3, unless there's something I really don't understand about density, but comparing these I got 5.179/5.513 = approx. 0.9394, but (mass_almagest / (radius_almagest^3)) / (mass_earth / (radius_earth^3)) came out to approx. 0.9353 by my calculation. It's a small difference, but I'm not sure whether it's a significant one by your standards or not since there may be secondary factors I'm unaware of (or you're using more precise numbers for Earth/Almagest than I did).

- Similarly, there was a (small) discrepancy re: surface gravity strength, as you give g_almagest / g_earth = 0.972. I'd expect the gravitational acceleration for a planet to be proportional to planet mass / radius^2 (granted just going off the equations I learned in Intro to Astrophysics, so there may well be more complex and precise models I'm unaware of you used here); comparing m_almagest / r_almagest^2 to m_earth / r_earth^2 gave me a ratio of approx. 0.9698 (again a difference in the ratio from expected on the order of a few thousandths, which I don't know if you consider significant or not).

Again, given the depth it looks like you're aiming for with this it may well be the case that you are familiar with and used much more complex and precise models than the basic equations I'm familiar with, in which case sorry to trouble you with my meager efforts. But I did notice the planet was larger and more massive but less dense and with lower gravity, so I had the sudden urge to try to check the numbers myself and you did ask. This sort of world construction with physical details like realistic geography and weather patterns taken into account is something I find fascinating, although my own preferences in world building, when aiming for relative realism, tend to lean towards plausibility rather than exactitude.

[Peter Toth]

Hello Azure Wings,

Thank you so much for the honest critique and its promptness; your response was just what I was looking for. First of all, the multiplicity of north-south mountain ranges on the massive continent (to the east) are justified, I hope, by the following tectonic map which shows plate boundaries coinciding with a total of four mountain ranges, counting from west to east.

Tectonics.jpg

As for the seven remaining mountain ranges, I reason they represent the folding of the same plates due to very vigorous horizontal plate movements; perhaps I should have marked boundaries there as well, but somehow neglected that aspect. After all, the planet is slightly younger than the Earth, at 4.28 billion years, and should have a bit more geological activity. Alternatively, the remaining mountain ranges could represent old plate collisions or the result of a continental suture, kind of like the Appalachian Mountains in the eastern U.S., which are nowhere near a plate boundary at the present time yet riddled with topography. The first possibility, however, is probably invalid, as the creation of so many long and narrow tectonic plates would involve an astronomically unlikely set of circumstances. Honestly, I have no idea, although I will certainly factor this in when I create my next conworld and avoid such unlikely types of topography, unless someone out there with a P.H.D in geology could offer legitimate reasons for them to be naturally-occurring.

The artifacts you found are indeed unintentional; they represent my neglect in properly rendering that part of the map, which I assumed everyone would fail to notice.

As for the precision with the basic properties of Almagest, you are correct in pointing out the discrepancy of the values from what they should be, which, again, I assumed wouldn’t be noticed. Assuming the mass and radius are absolute, I recalculated everything using following equation to determine density: (absolute mass)/(4/3*pi*radius^3), which gives me a value of 5.158 g/cc. For gravity, I use: (G*absolute mass)/radius^2, which gives 0.9713 g’s. (Of course, the G value in the first equation and the “4/3 pi” all cancel out algebraically once you frame the equation with respect to the Earth’s values.) Eventually, I will take into account other considerations, such as rotation rate and tidal stretching, which is notoriously difficult to calculate, let alone model. Very intimidating considering I only have a grade 12 math education.

Finally, I agree completely with your preference to strive towards plausibility rather than endlessly chasing that last decimal point. After all, I could derive each property to the hundredth decimal point, but for what practical use? I’d rather invest my energy and time into attending to other details, such as eventually considering what types of civilizations could develop on the surface of my conworld, given the layout of the continents and a multitude of other factors.

By the way, Cartographer’s Guild imposed a limit on the sizes of my graphics files; for more detailed maps and charts, please visit my website, www.compellingconworlds.com.

Again, thank you for the critique, and for such a warm welcome to Cartographer's Guild.

Peter