The mass does not only affect gravity (just repeating what Funky Pear and some others said) - the size of the planet also has an effect - smaller = stronger because density is what makes gravity not mass alone - thats why some suns seem stronger - cos they're equal mass but smaller
I have a few complaints: a: Im sure u cud make better use of Newtons law than this and b: enemies are useless because u can just charge at them firing madly and overpower anything they throw at u
V. good game but should have a save ablility - it can be very long, and u might want to stop in the middle - I enkoy the carnage once you have loads of turrets!