royalties to pay for someone else to do the work. Thorlin hired Richard Watts of Macrotronics to make a number of modifications. This included a new ending in which the player has to fly back out of the cavern in reverse before a timer runs out. Two months after sending it to APX, Christensen received his first royalty check for $18,000, and a phone call from an Atari executive who praised the game. Caverns eventually won the 1981 APX game contest, winning another $3,000, and in December 1982, Atari told Christensen he might receive up to $100,000 in royalties. Atari licensed the game in early 1982 for distribution in the main Atari catalog on diskette. This was the first APX to Atari move, among very few examples in total. When asked to collaborate on a cartridge-based port, Christensen declined, having started college. Atari released the cartridge version in 1983. Reception Computer Gaming World called Caverns of Mars "delightful ... addictive and excellently paced". It noted the age of the author and stated that the game "has all the look, feel, and play of a 'professional' program". Softline liked the game's use of checkpoints after losing a life, and concluded "This game is great; you'll find it difficult to pull yourself away". Compute! called Caverns of Marss graphics "impressive … an excellent use of the Atari's graphics capabilities," noting that the game takes advantage of a little-used mode allowing four colors per character. A Creative Computing reviewer opened with "Four minutes later. I was hooked. Four hours later, my wife dragged me away." and concluded by noting that "The Caverns of Mars has that indefinable "something" that makes it arcade-quality". The Addison-Wesley Book of Atari Software 1984 gave the game an overall B+ rating, calling it "fast-paced and addictive" and "great fun ... a must for any dedicated arcade game player". Electronic Fun gave it a 3.5 out of 5 rating, praising the action and pointing out only a few minor flaws. Caverns of Mars received a Certificate of Merit in the category of "Best Science Fiction/Fantasy Computer Game" at the 4th annual Arkie Awards, Legacy 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 horizontally and with rockets that launch upwards from the ground. The game was completed in 1981, but it