Martians

A small player-controlled ship moves laterally at the top of the screen from one side to the other, and can fire towards the bottom of the screen. The player can reverse the direction of the ship at any point, but it continually moves. Stationary enemy ships appear at the bottom of the screen that slowly scroll upwards. Enemy ships can only be destroyed by shooting their center, and the ship's flanks persist on the screen, blocking player fire. It's game over if the space ship hits an alien vessel.