Oct 31, 2009

This Orb's Solar System.

Well, i had decided that i wanted this Orb to be less hospitable than earth.  The simplest way to do that was to make it hotter or colder.  I decided to go with colder, since i could then mostly ignore those tricky parts of the texture map where it wraps around the pole and gets extremely distorted.

A yellow sun seemed somehow passé, so i tried some smaller stars on my Sun & Planet Creator Sheet.  It quickly became clear that this Orb's year was going to be significantly shorter.  I didn't want to bother with reckoning a year that was some weird fraction of an earth year, so i pushed the numbers around till this Orb's year was just over half an Earth year.


a screenshot of this Orb's system from StarGen with appropriate alterations.


I was kinda hoping that a class K orange sun would tend to work with differently colored photosynthesis, but as best i can understand from NASA Predicts Non-Green Plants on Other Planets, the optimal color of plant life is pretty much the same.  Leaves designed for a class K sun might look a little bluer than ours normally do.  But Earth-life photosynthesis should work fine with the light-- which is something i wanted anyway.

At first i had a lot of trouble figuring our how hot my planet would roughly be.  I hadn't found the formula now in the Celestial Architect.  I learned that only slight variations in insolation produced (from a human inhabitant's perspective) wildly different temperatures. Notice below that while This Orb gets 98.9% of the solar energy that Earth does, it's on average 12º F colder.  Human comfort is a tiny little bit of the extremely cold and hot temperatures the universe can provide.

There's a feed-back loop that you may or may not want to take into account.  Adding snow and ice tends to increase the albedo, which tends to reflect away more heat, which lowers the temperature and produces more snow and ice.  Fortunately the real world is more complicated than that.  We've had ice ages in the past and they have gone away, which wouldn't happen if climate were a simple as the math in my spreadsheet.

Approximating this Orb's albedo was a big pain.  Land ice/snow has a higher albedo than sea ice.  And i really couldn't find any good numbers for how much of the earth is covered with either or both.  There seem to be a lot of conflicting and vaguely defined answers on the 'net, but no specific ones.  In the end i made an educated guess and had to revise it down to keep the whole planet from freezing over.


So i ended up with this:

Sun "Ember"
Class K0 (orange)
Mass .78 of Sol


Orb
Average distance from Ember .651 AU
Rotation 28.73 Earth hours (28 hours ,43 min, 48 sec)
Orbital Period 194.843 Earth days (.525 earth years)
Orbital Period 159.824 Orb days
~ 1/6th of a day short of 160 days, so every 6 Orb Years they have an un-leap year with only 159 days
Year is generally divided into 8 months of 20 days.

Average Insolation 0.989
Albedo: 0.335
Greenhouse Effect 0.13

Approximate winter ice/snow coverage 45%
Approximate summer ice/snow coverage 35%
Average ice coverage 40%

Average temperature -12º F relative to Earth


These numbers are, i admit, not very exciting in themselves.  But they lay the foundation for what is to come.


I'm not very interested in the rest of the planets in the system at this point.  I ran a bunch of StarGen simulations to find a solar system that looked interesting.  I chose this one, since it had a good variety of planets and didn't seem too much like a copy off our solar system.  Ignore the 2nd planet out.  That's roughly where Orb goes.  I'll ignore the last 3 rockballs, demoting them from full planetary status like poor Pluto.  Then this Orb's system has a tidier number of planets, seven.

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