Mars

Mars is a side-scrolling twin-stick space themed shoot-em-up. You control a UFO that is under attack from the air and ground, and can shoot in any of eight directions. You need to avoid or annihilate the enemy fighters, their missiles, rockets lauched from the ground and the irregular terrain. You gain additional points for destroying radar installations, and may refuel by taking out fuel depots. At the end of each level, there are one or more rotating craft which can only be destroyed by firing through one of the four narrow slits around their main body. Once the bosses are dealt with, a new level starts at a higher level of difficulty.