I used to play this game in the late 80's or maybe early 90's

this is what i can remember about it:

at the start you could choose a planet to play - in the beginning you could choose one of two planets ( a red one (harder) or a sort of white coloured one) - the others got unlocked as you progressed.

It was a horizontal scroller - i think you were a man in a space suit on one planet and a space ship on another - or perhaps you were a space ship and if hit you turned into a space suited man that boosted around the screen with a blaster.

Any ideas? thanks!