Worldbuilding with Universe Sandbox

Universe Sandbox Icon
Image via Wikipedia

Even if you don’t create worlds for fiction or game worlds, The Universe Sandbox is a complete blast but if you do it’s an indispensable tool. It’s a multi-body simulator that lets you play with solar systems and galaxies, shoot a black hole by Earth, explode Jupiter, and much more. Selling for as little as $2.50 when Steam has it on sale, it could be the best game for less than the cost of a fast food meal you can buy.

You can have hours of fun just making your own simulations or playing with the ones that come with it. In addition to the sheer pleasure of smashing planets, you get a great feel for the forces that shape our universe. For instance, several sceintific papers suggests it was likley one or more earth size planets were shot out of the infant solar system. If you are like me, that kind of makes sense but in the end, it’s a little hard to wrap your head around it. Well, open up the Universe Sandbox, start tossing moons around or change the orbit of Jupiter and you will soon see just how easy it is for one passing object to cause another to go careening out of a solar system. No more is it an abstract idea, now it is a concept you can really feel. And when it comes to creating a world, that can be all the difference between a setting that limps along and one that really runs.

Tatooine's twin suns from the Star Wars saga.
Image via Wikipedia

Multi-sun systems have always intrigued me. From Tatooine and its two suns to Helliconia, these are fun settings but I’ve always wondered just how plausible these systems are. Sure recent studies suggest this system can have planets but what does that really mean? Especially for something like Tatooine where at first glance, that planet orbits two similar sized suns at similar distances (although I suppose they could dissimilar sized and a distance where they appear the same)?

Well, fire up your Universe Sandbox and have it. With the simulator, you can create a system and see how it works. As a first step, I wondered what it would be like it Neptune was turned into a dwarf sun of about 10 Jupiter masses. It’s trivial in the simulator: load it up the solar system, click on Nepture, change its mass and there you do. It certainly perturbs the out system bottoms, although not as much as you might think. What happens to Earth? Not a lot but it perceptible makes the orbit elliptical with a precessing axis.
It’s a little hard to see in the picture below but in the simulator you can see Earth  drifting closer and farther from the sun by maybe 3%. Doesn’t seem like much but can you imagine what the seasons would be like if on top of the one year seasonal cycle, there was a 15 year secondary variation with the energy from the sun varying by about 6% (0.97^2)? That is a tremendous change for something that seems a rather minor effect. Imagine what impact that could have on a world in a science fiction or fantasy setting. Every fifteen years you have extra hot summers and mild winters, vice versa on an offset of 7.5 years. Additionally you have another bright object in the sky. Haven’t done the math but probably something on the order of as bright as a full moon although no larger than Jupiter.

My first experiment was with a fairly small second sun in a regular orbit. What about a larger second sun in a more elliptical orbit? Here the problem is finding something stable, something where the planets don’t roast or go shooting out of the system. Interestingly, even though a second sun out past Neptune seems “pretty far away” and doesn’t grossly perturb the orbits of the inner planets, a 0.6 solar mass second sun almost always causes Mercury to go shooting out of the solar system fairly quickly as it gets nudged into an orbit near the sun and sling-shotted away. Even Earth and Venus start wobbling a lot, coming to share similar orbits until one or the other gets shot out as well. And, of course, the outer planets like Neptune, Uranus, Pluto and the other outer dwarf planets get shot away pretty quickly. So one early lesson: reduce the number of inner solar system planets. But, remove Venus, Mars and Mercury and you can get a reasonably stable Earth orbit at one AU without a whole lot of wobble- less than the wobble in the earlier Neptune system. But what does that mean for setting? Well, probably not as interesting. Basically means that you can have a distant, near solar sun in a somewhat eccentric orbit that allows a stable earth but it will be far enough away to be just a very bright star and it means the inner solar system needs to be a lot more empty. I supposed you can leave Venus or Mars in the inner system but while I only simulated for several centuries, it looked unstable: sooner or later one or the other planets would go zipping off into deep space.

How about a more Hellicona type binary system with the second sun on a very long, eccentric orbit with a period of several thousand years? I’ll confess I’m  not patient enough to simulate it. I think it could be constructed if the orbit did not take the sun too close to the first one (beyond, say, Neptune’s orbit) and you cleared out the inner system to avoid any nasty dynamics that might eject your Earth-type world. But the second sun would have to remain distant enough it wouldn’t look very Sun-like, no second sun in the sky like the Tatooine picture but maybe a period of time where the earth orbit is much more eccentric and the weather more extreme. I honestly don’t think you can get a Helliconia situation where you have centuries of hot followed by centuries of cold but I think you could get a situation where you have an Earth like planet in more eccentric orbits for 50 years with hotter and colder seasons followed by centuries of less eccentric orbits although I am not sure how stable that would be or how eccentric the planet’s orbit would become.

Anyway, as you can see, there is a lot to play with. There’s much you an do with the simulator and the real beauty of it as a world building tool is you can either try to set up an interesting situation you thought of and see what happens, or perhaps easier and better, play around with it and see what interesting systems occur.

Have fun with it!


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  1. Pingback: SpaceEngine: Go Anywhere in the Universe | M. Q. Allen

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