From WikiPedia: "Mars Mission II
Christensen followed Caverns in 1981 with a lesser-known sequel, known originally as Caverns of Mars II. This version is very similar to Scramble, scrolling sideways and featuring rockets that launched upwards from the ground. The game was completed in 1981, but for reasons that are not clear, it was not released. It would not be published until several years later by Antic Software, renamed Mars Mission II.["
LbnL the Antic Software release year was 1984.