The level of polish is quite impressive for a jam game.
In addition to the visuals and sounds, nice job playing around with archetypes for the planets' characterization without making them annoying.
The difficulty was also just right, almost forcing players to sacrifice planets on their first try, while making it quite feasible to make it unscathed on subsequent playthroughs.
Did you consider including further levels mixing both comets and asteroids ? At first I thought the game was hinting at it, but with the (well-executed) focus on narration, I'm not sure it was your intention after all.
Anyway, very nicely done.