Nice little game! I just bought Neptune :)
I think adding stars as background can help reduce weirdness of sun's motion, it currently looks like the sun just randomly walks around (but I get the idea, you are trying to have a minimal bounding box of all the planets and zoom the camera to fit it)
Also why did you decide to go with A B C instead of usual K M B ... ? Just wondering, because 10k 10m 10b feels more natural than 10a 10b 10c, just my opinion
Overall very nice :)