Caverns of Mars, by Greg Christensen, was the most popular title for the Atari Program Exchange (APX) line of software for the Atari 8-bit systems, resulting in upwards of $100,000 in royalties for Christensen alone.
You control a ship descending into a narrow cavern lined with glowing emplacements and fuel silos. Using your ship's twin cannons you can destroy all of them for points, but every fuel silo destroyed also gives you 5 units of fuel. Fuel decreases over time from 100, so destroying fuel silos is necessary to make it out alive. You control your rate of descent by moving closer to the edge of the screen, but this is much more dangerous and could result in destruction. If you have extra lives remaining you respawn, but are still limited by the fuel you have. After descending far enough you are rushed by rocket ships and martian fighters, which you must destroy or dodge to avoid. After this you descend into a narrow, glowing cavern and come into contact with the reactor at the bottom. You set the reactor to detonate, and must now ascend the cavern you just entered to escape before the reactor explodes. Should you die during this sequence, you are allowed to continue, but the countdown timer is not reset.
As difficulty increases, emplacements fire back, opening and closing doors, and there are floating mines which block the cavern and must be eliminated. There are five caverns in all, each significantly more difficult than the last.
This game closely resembles the side-scrolling shooter Scramble by Konami.
After its initial release through APX, the game was later published by Atari on both cartridge and disk as part of their product line for the Atari 8-bit computers.
The game was later hacked to run on an Atari 5200, but was never officially released there. The game was developed to a prototype stage for the Atari 2600, but wasn't released on the console. Said prototype would show up as one of the games present on the Atari Flashback 2, a plug-and-play 2600-style device containing 42 built-in games.
Greg Christensen eventually developed a sequel, known as Caverns of Mars II, but it wasn't released in its original time frame. Later, Antic published the sequel under the name Mars Mission II.