Lego Space Space subtheme in which the entire theme is "good", "bad", or "civilian". Life on Mars is a space theme released in 2001, around a time of increased curiosity about the red planet. The theme revolved around the concept of the lifeforms that could possibly exist on Mars. This was the first Space theme to feature two types of minifigures: human astronauts and Martian aliens. The sets denote peaceful coexistence between the two species on the planet Mars. The "Life on Mars" theme pioneered several unique aspects in Lego in general. It was the first Lego theme to utilize a pneumatic
The Gods of Mars to Earth in pre-technological eras, particularly with the inclusion of kingdoms, empires or religious societies. Spacecraft may appear, but are not central to the story (something which makes these tales distinct from Space Opera, where spaceships are usually a key focus of the narrative). There were some Planetary Romances prior to the publication of the Barsoom novels, but "A Princess of Mars" and "The Gods of Mars" and other novels in the Barsoom series were the most influential on the numerous similar stories that were published subsequently. Burroughs's vision of Mars was loosely inspired by astronomical speculation of the time,