# Help Me Build a Solar SystemDecember 13, 2013 10:10 PM   Subscribe

I want to build a solar system with a decent amount of verisimilitude, and the math and physics are killing me.

Ideally, I'd like some sort of program which can let me set a sun and planets and figure out basic things like length of the day, length of the year, tides, etc... I could just make it up, but I keep worrying I'll do something ridiculous that years down the road I'll look back and curse at. So far I have found a number of random solar system generators, but none which allow me to set some of the parameters and none which help with tides when there is a non-earth situation. Specifically, I want my planet to have either a few moons, or rings, and I can't figure out how to figure out how that would affect the tides and weather patterns. Bonus points for one which allows me to set a planetary tilt and figure out the temperature zones on the planet from it.
posted by Deoridhe to Science & Nature (4 answers total) 8 users marked this as a favorite

Have you looked at Universe Sandbox? I'm not sure that it'd necessarily be able to help with figuring out tides, but it does let you estimate the average surface temperature. Weather is difficult to simulate accurately, which is probably why most simulators don't bother.
posted by Aleyn at 11:26 PM on December 13, 2013 [2 favorites]

I don't know of a good solar system generator, but I can help you with a few of your questions.

The length of the year is determined by the mass of the star and the planet's distance from the star according to Kepler's Third Law. (Scroll down to the Law of Orbits).

Length of day is pretty much up to you, unless the planet is tidally locked (i.e., always keeps one face toward) to the star or its moon. In that case, the length of the day equals the length of the orbit. For example, the Moon orbits the Earth in 27.3 (earth-)days, and its rotation period (i.e. length of the day) is also 27.3 days, so that as it turns, it always keeps its "near" side toward Earth. Pluto and Charon, being similar in size and very close to one another, are mutually tidally locked, which I always thought would be fun to do on a game world. (A planet being tidally locked to its moon would lead to constant tides, with no variation in tidal height, incidentally.)

Tides with multiple moons are going to be really complicated, and you might as well determine the tidal height at any given time randomly, unless the moons are in resonant orbits, like the jovian moons Io, Europa, and Ganymede. For every one orbit of Ganymede, Io orbits four times and Europa orbits twice. A system of moons in resonance would lead to a regular, but not-earthlike, pattern of tides. Unless something very weird was going on, moons would not have any effect to speak of on weather.

Rings would not create variable tides, because the rings are uniform around the planet (and probably would not contain a lot of mass, anyway). They could possibly lead to the equatorial areas being cloudy all the time, as the dust-sized ring particles spiral inward under Poynting-Robertson drag, and seed clouds. This is what creates a thick aerosol haze on Saturn, for examples, which is visible as a wide, light-colored band at the equator. The regions of the planet that were in ringshadow would be a bit colder (depending on how thick the rings are). The shadow would move through a region in winter or early spring, depending on the region's latitude (and for higher latitudes, it wouldn't happen at all).
posted by BrashTech at 7:37 AM on December 14, 2013 [6 favorites]

(Whoops, sorry, at the Kepler's Laws link, scroll down to the Law of Periods.)
posted by BrashTech at 8:09 AM on December 14, 2013

Note that on Earth the tides are almost equally affected by the moon and the sun. So a tidally locked or moonless planet would still have tidal effects from its sun. They would just be much more predictable.
posted by Riemann at 1:38 PM on December 14, 2013 [1 favorite]

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