If you haven't seen this prime example of the strange yet wonderful Christmas-themed films from the late 1960s, you really need to watch this one. Basically, the Martians intercept a newscast talking about a hilarious figure called Santa Claus, and conclude that he is the cure to the serious depression that is impairing their children's otherwise intellectually gifted childhoods. So they kidnap him, leaving a psychotic robot in charge of the North Poleians. A brother-sister duo of humans stows away in the space craft, and (after a series of unfortunate events) manage to save Santa, convince the Martians to find humor in their strangely green lives, and overpower the psychotic robot. Thus, Christmas in the psychedelic age was saved.
It may make more sense if you drink heavily while watching it.