Playing dice with the universe

Wow. I found this amazingly addictive webapp thanks to one of the forums (fora?) I read regularly. You can create your own solar system using the stars/planets provided. Obviously, it’s not a solar system without at least one star, so the first star is provided for you.

If you play around with it for a bit, you discover one interesting fact. It is very, very difficult to create a multiple star system with planets in a stable orbit. I did it, but only by putting the stars in a very close binary and dropping the planet well outside their gravitational well. This works as long as the planet’s mass is negligible with respect to the sum of the stellar masses. Put too large a plant in, and BOOM!! The whole thing breaks apart. This same instability makes trinary (and even larger stellar multiples) just as unlikely.

Astronomers have discovered that the majority of stars are in binary systems. (Remember, that if you have the same number of single and binary solar systems, then 2/3 of the total number of stars are in the binaries….so it’s not as significant a statement as it may sound at first.) Playing around with this program helps to demonstrate why that would be. As you can see, the binaries have a tendency to either destroy or eject their planets. This means that the number of solar systems with lovely stable planetary systems like our own isn’t as prevalent as you might think. Thankfully, even a small percentage of a very, very, very large number (the number of stars in the universe) is itself another very, very large number (the number of systems with planets in stable orbits).

A friend asked me how realistic this is. Well, it’s as realistic as projecting a three-dimensional dynamic system with all its accompanying chaotic complexities (differential rotation, oblateness, density gradients, solar wind, etc.) can be. In other words…it’s relatively simplistic. But that doesn’t stop it from being a whole lot of FUN!

So go ahead and throw dice in your own little corner of the cosmos. And Don’t Panic!

On Edit: In her never-ending quest to prove me wrong, my daughter has managed a binary system with multiple planets. The innermost one has an orbit that obviously precesses, as do the orbits of the two stars. We’ve let it run for several hours now and it shows no sign of major perturbations. The proof can be seen below.

Binary system with multiple planets in stable orbits

Reminder to self – never tell an artist something can’t be done…they will find a way.

Edit #2: I left it running all night and you can see how the two planets have set up a resonance. The precession of the orbit seems to be occurring faster now, and it’s possible that the inner planet might finally be ejected from the system due to the gravitational effects of the outer planet. Notice they are both “Earth” type planets. Had we included a higher mass body, this effect would have been seen much more quickly.

Same binary system, 12 hours later

Edit #3: Okay, after 24 hours the planets are still bound, precessing, and seemingly stable around their binary primaries. No reason to think they’ll be ejected now! Score one point to the daughter, she wins this round…


3 Responses to “Playing dice with the universe”

  1. I think what this program really proves is that Tatooine is a very very rare place.

  2. OK, yes, that’s impressive and a fun toy. I wish the planets and stars were rendered a little differently. Those are BIG planets. And BIG stars for such a small field. Still, fun. And no, I haven’t set up any stable planetary orbits in binary systems yet. It’s dang hard.

    Now gimme some black holes, accretion disks, and Roche lobe overflows. Let’s pump the energy here!

  3. Very fun app, thanks for the link! I’m sure my amateur astronomer will get a kick out of it. My only complaint is the scale, it needs to be zoomed out quite a bit. If you’re going to have stable orbits I think they would be easier to achieve if you’re not within four solar radii.

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