27 January 2011

For Those Who Like Math, Geology, or Astronomy! (Or, How to Make an Alien World)

Long ago I did some research and a lot of speculation and came up with the following data for use in the original Dream Land novel. Like I said, it was long ago. It seemed right at the time but I have not checked further on the accuracy of the Earth data or plausibility of the data for Ghoupallesz.

Anyway, it serves as an example of the kind of geophysical understanding that is necessary (in my opinion) for creating alien worlds. Things don't just happen, they happen for a reason! Gravity, atmosphere, etc. affect how characters act and how the lifeforms act and that may also influence cultural aspects of an alien society.


MEASUREMENT                        EARTH                           GHOUPALLESZ

age                                                   4.5 billion years                3.8 billion years

distance from sun                              93 million miles                 (not calculated due to having 2 suns)

mass (actual)                                   6600(to 18th power) tons  6072(to 18th power) tons

mass (proportional)                          100                                  84

axial rotation (length of day)              23:56:4.09                       29:50:24.16

axial tilt                                             23°                                  14°

orbit revolution (length of year)         365 days                          408 days
                                                                                                 (of the longer Ghoupallean days)

diameter (equatorial)                        7926.41 miles                  5934.286 miles

              (polar)                               7899.83 miles                  5922.819 miles

circumference (equatorial)                24,901.55 miles               22,909.426 miles

              (polar)                               24,859.82 miles               22,897.167 miles

surface area                                     196,951,000 sq. miles     181,194,900 sq. miles

land area                                         57,259,000 sq. miles        94,221,348 sq. miles

water area                                       139,692,000 sq. miles      86,973,552 sq. miles

land-water %                                  30 - 70                             52 - 48

gravity ratio                                     100                                  92

highest land point                             29,028 ft.                         42,880 ft.

lowest land point                              -1299 ft.                          -2712 ft.

deepest ocean point                         -36,198 ft.                       -28,453 ft.

average ocean depth                        -12,450 ft.                       -14,165 ft.

atmospheric composition:

nitrogen                                            78%                                72.8%
oxygen                                             21%                                26.4%
other                                                1%                                  0.8%

surface chemical composition (upper 1% of planetary crust):

oxygen                                             46.6%                             49.2%
silicon                                               27.7%                            19.8%
aluminum                                          8.1%                               5.7%
iron                                                  5.0%                               10.3%
calcium                                             3.6%                               4.1%
sodium                                             2.8%                               4.5%
potassium                                         2.6%                               2.9%
magnesium                                       2.0%                               1.7%
other                                                1.6%                               1.8%

Special Notes & Observations (these were written in the 1980s):

Like Earth, Ghoupallesz is wider around its equator than around its polar longitude, but the difference is less for Ghoupallesz.

Water is lighter than land, so a planet with more land surface would be heavier for the same size, or would it be lighter because of the absence of water (including water covering any land area)?

Different, heavier elements in mantle would make a same-sized planet heavier (thus stronger gravity?)

If a planet has 30% land to 70% water surface area (Earth) and, without changing any land features, half of the water was removed (making it 65% land to 35% water), air would fill the space left by the removed water (remaining water settling into the lowest basins)--and air being lighter than water, the planet would become lighter?

If Ghoupallesz were the same size as Earth (surface area and circumference), it would be heavier (8%) due to a composition of heavier elements. Gravity effect?

Because Ghoupallesz is actually 8% smaller in size, the heavier weight per cubic foot of planetary matter would make it equal to Earth's mass?

Ghoupallesz revolves on its axis more slowly than Earth, therefore...one Ghoupallesz day equals 29.84 Earth hours. Ghoupallesz has 408 of those longer days to make a year.

Earth tilts at 23° but the Ghoupallesz axis tilts at only 14°, thereby making the seasons on Ghoupallesz more even in temperature and the amount of change from one season to another; weather patterns are more stable, seasons less distinct or variable.

“If Earth’s gravity is E=1 and the gravity of Ghoupallesz is 10% less (due to 10% less land mass), what is the difference in effect on athletic ability?”  (If a man can jump 10 feet—standing broad jump—on Earth, the same man can jump 11 feet—10% further—on Ghoupallesz?)



  1. *dies* I can't decide whether this is way cool or totally overwhelming. In a way, it makes something that I had never thought I could do (world building) possible because... you know... I can do math. But i could NEVER think of all the details I needed to consider! Wow.

  2. I think I think too much about stuff I don't need to think about and don't think enough about stuff I should think about. What do you think?

    I needed my Earth characters to have some advantage over the local "aliens", so I made the alien world smaller (lighter gravity than what they are used to) and more oxygen (easier to breathe in strenuous circumstances).

  3. This is amazing world building. You've really thought it out! I wish I could kick in here and give some real feedback, but I am physics-challenged.