Saturn has its famous rings and Jupiter is the granddaddy of the solar system, but no planet has entranced earthlings quite like Mars.

Humans have launched 40 spacecraft to the Red Planet, lured by the prospect that life might once have existed in what is now dry rocks and sand. The latest machine to make the journey is NASA’s Mars Science Laboratory, a hulking, souped-up lab-on-wheels that will plunge toward the Martian surface next week.

But even as excitement builds, some wonder: Is Mars exploration a good investment?