Perhaps they could survive the vaccuum of space just long enough to land on another planet? It's a longshot, of course, but it'd just take one or two to seed a planet.
Is that some kind of bug, or are sardine systems a feature? Also, are you open to ideas for creatures? Because I have an idea for a sarlacc-like monster that can whip your probe off course if you get too close.
As was pointed out before, orbits are next to impossible, because 1) The planets are stationary, meaning their gravity tugs are consistent rather than periodic. 2) The planets are building sized, making tidal effects a Kraken to deal with.
Some questions: -How many different kinds of creatures are there going to be? A few dozen? A few hundred? -Will there be binary and multiple stars in the game? -How about planetary rings?
How many other kinds of planets will there be than the ones shown in the prototype? Will there be preset "flavors" the engine will use (lava, snow, ocean, moon-ish...) or will it be completely random?